v0.9.0-beta.3

Plus `UserDataFields::add_meta_field()` for static meta fields.
Fix propagating fields to wrapped UserData types.

.github/workflows/coverage.yml

@@ -14,7 +14,7 @@ jobs:
 
       - name: Generate coverage report
         run: |
-          cargo tarpaulin --out xml --tests --exclude-files benches/* --exclude-files src/ffi/*/*
+          cargo tarpaulin --out xml --tests --exclude-files benches/* --exclude-files mlua-sys/src/*/*
 
       - name: Upload report to codecov.io
         uses: codecov/codecov-action@v3

.github/workflows/main.yml

@@ -9,7 +9,7 @@ jobs:
       matrix:
         os: [ubuntu-22.04, macos-latest, windows-latest]
         rust: [stable]
-        lua: [lua54, lua53, lua52, lua51, luajit, luau]
+        lua: [lua54, lua53, lua52, lua51, luajit, luau, luau-jit]
         include:
           - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
@@ -27,7 +27,7 @@ jobs:
       - name: Build ${{ matrix.lua }} vendored
         run: |
           cargo build --features "${{ matrix.lua }},vendored"
-          cargo build --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+          cargo build --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable"
         shell: bash
       - name: Build ${{ matrix.lua }} pkg-config
         if: ${{ matrix.os == 'ubuntu-22.04' }}
@@ -50,7 +50,7 @@ jobs:
           toolchain: stable
           target: aarch64-apple-darwin
       - name: Cross-compile
-        run: cargo build --target aarch64-apple-darwin --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        run: cargo build --target aarch64-apple-darwin --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable"
 
   build_aarch64_cross_ubuntu:
     name: Cross-compile to aarch64-unknown-linux-gnu
@@ -71,7 +71,7 @@ jobs:
           sudo apt-get install -y --no-install-recommends gcc-aarch64-linux-gnu libc6-dev-arm64-cross
         shell: bash
       - name: Cross-compile
-        run: cargo build --target aarch64-unknown-linux-gnu --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        run: cargo build --target aarch64-unknown-linux-gnu --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable"
         shell: bash
 
   build_armv7_cross_ubuntu:
@@ -93,7 +93,7 @@ jobs:
           sudo apt-get install -y --no-install-recommends gcc-arm-linux-gnueabihf libc-dev-armhf-cross
         shell: bash
       - name: Cross-compile
-        run: cargo build --target armv7-unknown-linux-gnueabihf --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        run: cargo build --target armv7-unknown-linux-gnueabihf --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable"
         shell: bash
 
   test:
@@ -104,7 +104,7 @@ jobs:
       matrix:
         os: [ubuntu-22.04, macos-latest, windows-latest]
         rust: [stable, nightly]
-        lua: [lua54, lua53, lua52, lua51, luajit, luajit52, luau]
+        lua: [lua54, lua53, lua52, lua51, luajit, luajit52, luau, luau-jit]
         include:
           - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
@@ -118,17 +118,18 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
           target: ${{ matrix.target }}
-      - uses: Swatinem/rust-cache@v1
+      - uses: Swatinem/rust-cache@v2
       - name: Run ${{ matrix.lua }} tests
         run: |
           cargo test --features "${{ matrix.lua }},vendored"
           cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+          cargo test --features "${{ matrix.lua }},vendored,async,serialize,macros,parking_lot,unstable"
         shell: bash
       - name: Run compile tests (macos lua54)
         if: ${{ matrix.os == 'macos-latest' && matrix.lua == 'lua54' }}
         run: |
           TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored" -- --ignored
-          TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot" -- --ignored
+          TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable" -- --ignored
         shell: bash
 
   test_with_sanitizer:
@@ -139,7 +140,7 @@ jobs:
       matrix:
         os: [ubuntu-22.04]
         rust: [nightly]
-        lua: [lua54, lua53, lua52, lua51, luajit, luau]
+        lua: [lua54, lua53, lua52, lua51, luajit, luau, luau-jit]
         include:
           - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
@@ -149,12 +150,13 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
           target: ${{ matrix.target }}
-      - uses: Swatinem/rust-cache@v1
+      - uses: Swatinem/rust-cache@v2
       - name: Run ${{ matrix.lua }} tests with address sanitizer
         run: |
-          RUSTFLAGS="-Z sanitizer=address" \
-            cargo test --tests --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot" --target x86_64-unknown-linux-gnu -- --skip test_too_many_recursions
+            cargo test --tests --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable" --target x86_64-unknown-linux-gnu -- --skip test_too_many_recursions
         shell: bash
+        env:
+          RUSTFLAGS: -Z sanitizer=address
 
   test_modules:
     name: Test modules
@@ -176,7 +178,7 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
           target: ${{ matrix.target }}
-      - uses: Swatinem/rust-cache@v1
+      - uses: Swatinem/rust-cache@v2
       - name: Run ${{ matrix.lua }} module tests
         run: |
           (cd tests/module && cargo build --release --features "${{ matrix.lua }}")
@@ -220,7 +222,7 @@ jobs:
     runs-on: ubuntu-22.04
     strategy:
       matrix:
-        lua: [lua54, lua53, lua52, lua51, luajit, luau]
+        lua: [lua54, lua53, lua52, lua51, luajit, luau, luau-jit]
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@stable
@@ -230,4 +232,4 @@ jobs:
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          args: --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+          args: --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot,unstable"

.gitignore

@@ -4,3 +4,4 @@ Cargo.lock
 
 .vscode/
 .DS_Store
+.stignore

CHANGELOG.md

@@ -1,14 +1,63 @@
-## v0.8.10
+## v0.9.0-beta.3
 
-- Update to Luau 0.590 (luau0-src to 0.7.x)
-- Fix loading luau code starting with \t
-- Pin lua-src and luajit-src versions
+- Added `OwnedAnyUserData::take()`
+- Switch to `DeserializeOwned`
+- Overwrite error context when called multiple times
+- New feature flag `luau-jit` to enable (experimental) Luau codegen backend
+- Set `__name` field in userdata metatable
+- Added `Value::to_string()` method similar to `luaL_tolstring`
+- Lua 5.4.6
+- Application data container now allows to mutably and immutably borrow different types at the same time
+- Performance optimizations
+- Support getting and setting environment for Lua functions.
+- Added `UserDataFields::add_field()` method to add static fields to UserData
 
-## v0.8.9
+Breaking changes:
+- Require environment to be a `Table` instead of `Value` in Chunks.
+- `AsChunk::env()` renamed to `AsChunk::environment()`
 
-- Update minimal (vendored) Lua 5.4 to 5.4.6
-- Use `lua_closethread` instead of `lua_resetthread` in vendored mode (Lua 5.4.6)
-- Allow deserializing Lua null into unit (`()`) or unit struct.
+## v0.9.0-beta.2
+
+New features:
+- Added `Thread::set_hook()` function to set hook on threads
+- Added pretty print to the Debug formatting to Lua `Value` and `Table`
+- ffi layer moved to `mlua-sys` crate
+- Added OwnedString (unstable)
+
+Breaking changes:
+- Refactor `HookTriggers` (make it const)
+
+## v0.9.0-beta.1
+
+New features:
+- Owned Lua types (unstable feature flag)
+- New functions `Function::wrap`/`Function::wrap_mut`/`Function::wrap_async`
+- `Lua::register_userdata_type()` to register a custom userdata types (without requiring `UserData` trait)
+- `Lua::create_any_userdata()`
+- Added `create_userdata_ref`/`create_userdata_ref_mut` for scopes
+- Added `AnyUserDataExt` trait with auxiliary functions for `AnyUserData`
+- Added `UserDataRef` and `UserDataRefMut` type wrapped that implement `FromLua`
+- Improved error handling:
+  * Improved error reporting when calling Rust functions from Lua.
+  * Added `Error::BadArgument` to help identify bad argument position or name
+  * Added `ErrorContext` extension trait to attach additional context to `Error`
+
+Breaking changes:
+- Refactored `AsChunk` trait
+- `ToLua`/`ToLuaMulti` renamed to `IntoLua`/`IntoLuaMulti`
+- Renamed `to_lua_err` to `into_lua_err`
+- Removed `FromLua` impl for `T: UserData+Clone`
+- Removed `Lua::async_scope`
+- Added `&Lua` arg to Luau interrupt callback
+
+Other:
+- Better Debug for String
+- Allow deserializing values from serializable UserData using `Lua::from_value()` method
+- Added `Table::clear()` method
+- Added `Error::downcast_ref()` method
+- Support setting memory limit for Lua 5.1/JIT/Luau
+- Support setting module name in `#[lua_module(name = "...")]` macro
+- Minor fixes and improvements
 
 ## v0.8.8
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua"
-version = "0.8.10" # remember to update mlua_derive
+version = "0.9.0-beta.3" # remember to update mlua_derive
 authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@chucklefish.org>"]
 edition = "2021"
 repository = "https://github.com/khvzak/mlua"
@@ -9,60 +9,55 @@ readme = "README.md"
 keywords = ["lua", "luajit", "luau", "async", "scripting"]
 categories = ["api-bindings", "asynchronous"]
 license = "MIT"
-links = "lua"
-build = "build/main.rs"
 description = """
 High level bindings to Lua 5.4/5.3/5.2/5.1 (including LuaJIT) and Roblox Luau
 with async/await features and support of writing native Lua modules in Rust.
 """
 
 [package.metadata.docs.rs]
-features = ["lua54", "vendored", "async", "send", "serialize", "macros", "parking_lot"]
+features = ["lua54", "vendored", "async", "send", "serialize", "macros", "parking_lot", "unstable"]
 rustdoc-args = ["--cfg", "docsrs"]
 
 [workspace]
 members = [
     "mlua_derive",
+    "mlua-sys",
 ]
 
 [features]
-lua54 = []
-lua53 = []
-lua52 = []
-lua51 = []
-luajit = []
-luajit52 = ["luajit"]
-luau = ["luau0-src"]
-vendored = ["lua-src", "luajit-src"]
-module = ["mlua_derive"]
-async = ["futures-core", "futures-task", "futures-util"]
+lua54 = ["ffi/lua54"]
+lua53 = ["ffi/lua53"]
+lua52 = ["ffi/lua52"]
+lua51 = ["ffi/lua51"]
+luajit = ["ffi/luajit"]
+luajit52 = ["luajit", "ffi/luajit52"]
+luau = ["ffi/luau"]
+luau-jit = ["luau", "ffi/luau-codegen"]
+vendored = ["ffi/vendored"]
+module = ["mlua_derive", "ffi/module"]
+async = ["futures-util"]
 send = []
-serialize = ["serde", "erased-serde"]
+serialize = ["serde", "erased-serde", "serde-value"]
 macros = ["mlua_derive/macros"]
+unstable = []
 
 [dependencies]
-mlua_derive = { version = "=0.8.0", optional = true, path = "mlua_derive" }
-bstr = { version = "0.2", features = ["std"], default_features = false }
+mlua_derive = { version = "=0.9.0-beta.2", optional = true, path = "mlua_derive" }
+bstr = { version = "1.0", features = ["std"], default_features = false }
 once_cell = { version = "1.0" }
 num-traits = { version = "0.2.14" }
 rustc-hash = "1.0"
-futures-core = { version = "0.3.5", optional = true }
-futures-task = { version = "0.3.5", optional = true }
-futures-util = { version = "0.3.5", optional = true }
+futures-util = { version = "0.3", optional = true, default-features = false, features = ["std"] }
 serde = { version = "1.0", optional = true }
 erased-serde = { version = "0.3", optional = true }
+serde-value = { version = "0.7", optional = true }
 parking_lot = { version = "0.12", optional = true }
 
-[build-dependencies]
-cc = { version = "1.0" }
-pkg-config = { version = "0.3.17" }
-lua-src = { version = ">= 546.0.0, < 546.1.0", optional = true }
-luajit-src = { version = ">= 210.4.0, < 210.5.0", optional = true }
-luau0-src = { version = "0.7.0", optional = true }
+ffi = { package = "mlua-sys", version = "0.2.0", path = "mlua-sys" }
 
 [dev-dependencies]
-rustyline = "10.0"
-criterion = { version = "0.3.4", features = ["html_reports", "async_tokio"] }
+rustyline = "11.0"
+criterion = { version = "0.5", features = ["async_tokio"] }
 trybuild = "1.0"
 futures = "0.3.5"
 hyper = { version = "0.14", features = ["client", "server"] }
@@ -73,6 +68,7 @@ serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 maplit = "1.0"
 tempfile = "3"
+static_assertions = "1.0"
 
 [[bench]]
 name = "benchmark"

README.md

@@ -7,9 +7,9 @@
 [crates.io]: https://crates.io/crates/mlua
 [API Documentation]: https://docs.rs/mlua/badge.svg
 [docs.rs]: https://docs.rs/mlua
-[Coverage Status]: https://codecov.io/gh/khvzak/mlua/branch/v0.8/graph/badge.svg?token=99339FS1CG
+[Coverage Status]: https://codecov.io/gh/khvzak/mlua/branch/master/graph/badge.svg?token=99339FS1CG
 [codecov.io]: https://codecov.io/gh/khvzak/mlua
-[MSRV]: https://img.shields.io/badge/rust-1.56+-brightgreen.svg?&logo=rust
+[MSRV]: https://img.shields.io/badge/rust-1.63+-brightgreen.svg?&logo=rust
 
 [Guided Tour] | [Benchmarks] | [FAQ]
 
@@ -17,6 +17,10 @@
 [Benchmarks]: https://github.com/khvzak/script-bench-rs
 [FAQ]: FAQ.md
 
+> **Note**
+>
+> Please see the [v0.8](https://github.com/khvzak/mlua/tree/v0.8) branch for the stable versions of `mlua` released to crates.io.
+
 `mlua` is bindings to [Lua](https://www.lua.org) programming language for Rust with a goal to provide
 _safe_ (as far as it's possible), high level, easy to use, practical and flexible API.
 
@@ -41,6 +45,7 @@ Below is a list of the available feature flags. By default `mlua` does not enabl
 * `luajit`: activate [LuaJIT] support
 * `luajit52`: activate [LuaJIT] support with partial compatibility with Lua 5.2
 * `luau`: activate [Luau] support (auto vendored mode)
+* `luau-jit`: activate [Luau] support with experimental jit backend. This is unstable feature and not recommended to use.
 * `vendored`: build static Lua(JIT) library from sources during `mlua` compilation using [lua-src] or [luajit-src] crates
 * `module`: enable module mode (building loadable `cdylib` library for Lua)
 * `async`: enable async/await support (any executor can be used, eg. [tokio] or [async-std])
@@ -48,6 +53,7 @@ Below is a list of the available feature flags. By default `mlua` does not enabl
 * `serialize`: add serialization and deserialization support to `mlua` types using [serde] framework
 * `macros`: enable procedural macros (such as `chunk!`)
 * `parking_lot`: support UserData types wrapped in [parking_lot]'s primitives (`Arc<Mutex>` and `Arc<RwLock>`)
+* `unstable`: enable **unstable** features. The public API of these features may break between releases.
 
 [5.4]: https://www.lua.org/manual/5.4/manual.html
 [5.3]: https://www.lua.org/manual/5.3/manual.html

benches/benchmark.rs

@@ -120,7 +120,7 @@ fn call_sum_callback(c: &mut Criterion) {
 }
 
 fn call_async_sum_callback(c: &mut Criterion) {
-    let options = LuaOptions::new().thread_cache_size(1024);
+    let options = LuaOptions::new().thread_pool_size(1024);
     let lua = Lua::new_with(LuaStdLib::ALL_SAFE, options).unwrap();
     let callback = lua
         .create_async_function(|_, (a, b, c): (i64, i64, i64)| async move {
@@ -272,7 +272,7 @@ fn call_async_userdata_method(c: &mut Criterion) {
         }
     }
 
-    let options = LuaOptions::new().thread_cache_size(1024);
+    let options = LuaOptions::new().thread_pool_size(1024);
     let lua = Lua::new_with(LuaStdLib::ALL_SAFE, options).unwrap();
     lua.globals().set("userdata", UserData(10)).unwrap();
 

build/find_dummy.rs

@@ -1,5 +0,0 @@
-use std::path::PathBuf;
-
-pub fn probe_lua() -> Option<PathBuf> {
-    None
-}

build/main.rs

@@ -1,115 +0,0 @@
-#[cfg_attr(
-    any(
-        feature = "luau",
-        all(
-            feature = "vendored",
-            any(
-                feature = "lua54",
-                feature = "lua53",
-                feature = "lua52",
-                feature = "lua51",
-                feature = "luajit"
-            )
-        )
-    ),
-    path = "find_vendored.rs"
-)]
-#[cfg_attr(
-    all(
-        not(feature = "vendored"),
-        any(
-            feature = "lua54",
-            feature = "lua53",
-            feature = "lua52",
-            feature = "lua51",
-            feature = "luajit"
-        )
-    ),
-    path = "find_normal.rs"
-)]
-#[cfg_attr(
-    not(any(
-        feature = "lua54",
-        feature = "lua53",
-        feature = "lua52",
-        feature = "lua51",
-        feature = "luajit",
-        feature = "luau"
-    )),
-    path = "find_dummy.rs"
-)]
-mod find;
-
-fn main() {
-    #[cfg(not(any(
-        feature = "lua54",
-        feature = "lua53",
-        feature = "lua52",
-        feature = "lua51",
-        feature = "luajit",
-        feature = "luau"
-    )))]
-    compile_error!(
-        "You must enable one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau"
-    );
-
-    #[cfg(all(
-        feature = "lua54",
-        any(
-            feature = "lua53",
-            feature = "lua52",
-            feature = "lua51",
-            feature = "luajit",
-            feature = "luau"
-        )
-    ))]
-    compile_error!(
-        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau"
-    );
-
-    #[cfg(all(
-        feature = "lua53",
-        any(
-            feature = "lua52",
-            feature = "lua51",
-            feature = "luajit",
-            feature = "luau"
-        )
-    ))]
-    compile_error!(
-        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau"
-    );
-
-    #[cfg(all(
-        feature = "lua52",
-        any(feature = "lua51", feature = "luajit", feature = "luau")
-    ))]
-    compile_error!(
-        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau"
-    );
-
-    #[cfg(all(feature = "lua51", any(feature = "luajit", feature = "luau")))]
-    compile_error!(
-        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau"
-    );
-
-    #[cfg(all(feature = "luajit", feature = "luau"))]
-    compile_error!(
-        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau"
-    );
-
-    // We don't support "vendored module" mode on windows
-    #[cfg(all(feature = "vendored", feature = "module", target_os = "windows"))]
-    compile_error!(
-        "Vendored (static) builds are not supported for modules on Windows.\n"
-            + "Please, use `pkg-config` or custom mode to link to a Lua dll."
-    );
-
-    #[cfg(all(feature = "luau", feature = "module"))]
-    compile_error!("Luau does not support module mode");
-
-    #[cfg(any(not(feature = "module"), target_os = "windows"))]
-    find::probe_lua();
-
-    println!("cargo:rerun-if-changed=build");
-}

examples/async_http_client.rs

@@ -12,7 +12,7 @@ impl UserData for BodyReader {
         methods.add_async_function("read", |lua, reader: AnyUserData| async move {
             let mut reader = reader.borrow_mut::<Self>()?;
             if let Some(bytes) = reader.0.data().await {
-                let bytes = bytes.to_lua_err()?;
+                let bytes = bytes.into_lua_err()?;
                 return Some(lua.create_string(&bytes)).transpose();
             }
             Ok(None)
@@ -26,8 +26,8 @@ async fn main() -> Result<()> {
 
     let fetch_url = lua.create_async_function(|lua, uri: String| async move {
         let client = HyperClient::new();
-        let uri = uri.parse().to_lua_err()?;
-        let resp = client.get(uri).await.to_lua_err()?;
+        let uri = uri.parse().into_lua_err()?;
+        let resp = client.get(uri).await.into_lua_err()?;
 
         let lua_resp = lua.create_table()?;
         lua_resp.set("status", resp.status().as_u16())?;
@@ -37,7 +37,7 @@ async fn main() -> Result<()> {
             headers
                 .entry(key.as_str())
                 .or_insert(Vec::new())
-                .push(value.to_str().to_lua_err()?);
+                .push(value.to_str().into_lua_err()?);
         }
 
         lua_resp.set("headers", headers)?;

examples/async_http_reqwest.rs

@@ -10,8 +10,8 @@ async fn main() -> Result<()> {
         let resp = reqwest::get(&uri)
             .await
             .and_then(|resp| resp.error_for_status())
-            .to_lua_err()?;
-        let json = resp.json::<serde_json::Value>().await.to_lua_err()?;
+            .into_lua_err()?;
+        let json = resp.json::<serde_json::Value>().await.into_lua_err()?;
         lua.to_value(&json)
     })?;
 

examples/guided_tour.rs

@@ -1,7 +1,9 @@
 use std::f32;
 use std::iter::FromIterator;
 
-use mlua::{chunk, Function, Lua, MetaMethod, Result, UserData, UserDataMethods, Variadic};
+use mlua::{
+    chunk, FromLua, Function, Lua, MetaMethod, Result, UserData, UserDataMethods, Value, Variadic,
+};
 
 fn main() -> Result<()> {
     // You can create a new Lua state with `Lua::new()`. This loads the default Lua std library
@@ -30,7 +32,7 @@ fn main() -> Result<()> {
             global = 'foo'..'bar'
         "#,
     )
-    .set_name("example code")?
+    .set_name("example code")
     .exec()?;
     assert_eq!(globals.get::<_, String>("global")?, "foobar");
 
@@ -151,6 +153,16 @@ fn main() -> Result<()> {
     #[derive(Copy, Clone)]
     struct Vec2(f32, f32);
 
+    // We can implement `FromLua` trait for our `Vec2` to return a copy
+    impl<'lua> FromLua<'lua> for Vec2 {
+        fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
+            match value {
+                Value::UserData(ud) => Ok(*ud.borrow::<Self>()?),
+                _ => unreachable!(),
+            }
+        }
+    }
+
     impl UserData for Vec2 {
         fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
             methods.add_method("magnitude", |_, vec, ()| {

examples/module/Cargo.toml

@@ -2,7 +2,7 @@
 name = "rust_module"
 version = "0.0.0"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
-edition = "2018"
+edition = "2021"
 
 [lib]
 crate-type = ["cdylib"]

examples/repl.rs

@@ -5,7 +5,7 @@ use rustyline::Editor;
 
 fn main() {
     let lua = Lua::new();
-    let mut editor = Editor::<()>::new().expect("Failed to make rustyline editor");
+    let mut editor = Editor::<(), _>::new().expect("Failed to make rustyline editor");
 
     loop {
         let mut prompt = "> ";
@@ -19,7 +19,7 @@ fn main() {
 
             match lua.load(&line).eval::<MultiValue>() {
                 Ok(values) => {
-                    editor.add_history_entry(line);
+                    editor.add_history_entry(line).unwrap();
                     println!(
                         "{}",
                         values

mlua-sys/Cargo.toml

@@ -0,0 +1,41 @@
+[package]
+name = "mlua-sys"
+version = "0.2.0"
+authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
+edition = "2021"
+repository = "https://github.com/khvzak/mlua"
+documentation = "https://docs.rs/mlua-sys"
+readme = "README.md"
+categories = ["external-ffi-bindings"]
+license = "MIT"
+links = "lua"
+build = "build/main.rs"
+description = """
+Low level (FFI) bindings to Lua 5.4/5.3/5.2/5.1 (including LuaJIT) and Roblox Luau
+"""
+
+[package.metadata.docs.rs]
+features = ["lua54", "vendored"]
+rustdoc-args = ["--cfg", "docsrs"]
+
+[features]
+lua54 = []
+lua53 = []
+lua52 = []
+lua51 = []
+luajit = []
+luajit52 = ["luajit"]
+luau = ["luau0-src"]
+luau-codegen = ["luau"]
+vendored = ["lua-src", "luajit-src"]
+module = []
+
+[dependencies]
+
+[build-dependencies]
+cc = "1.0"
+cfg-if = "1.0"
+pkg-config = "0.3.17"
+lua-src = { version = ">= 546.0.0, < 550.0.0", optional = true }
+luajit-src = { version = ">= 210.4.0, < 220.0.0", optional = true }
+luau0-src = { version = "0.5.8", optional = true }

mlua-sys/README.md

@@ -0,0 +1,8 @@
+# mlua-sys
+
+Low level (FFI) bindings to Lua 5.4/5.3/5.2/5.1 (including LuaJIT) and Roblox [Luau].
+
+Intended to be consumed by the [mlua] crate.
+
+[Luau]: https://github.com/Roblox/luau
+[mlua]: https://crates.io/crates/mlua

mlua-sys/build/find_normal.rs

@@ -8,7 +8,7 @@ fn get_env_var(name: &str) -> String {
     match env::var(name) {
         Ok(val) => val,
         Err(env::VarError::NotPresent) => String::new(),
-        Err(err) => panic!("cannot get {}: {}", name, err),
+        Err(err) => panic!("cannot get {name}: {err}"),
     }
 }
 
@@ -37,8 +37,8 @@ pub fn probe_lua() -> Option<PathBuf> {
             if get_env_var("LUA_LINK") == "static" {
                 link_lib = "static=";
             };
-            println!("cargo:rustc-link-search=native={}", lib_dir);
-            println!("cargo:rustc-link-lib={}{}", link_lib, lua_lib);
+            println!("cargo:rustc-link-search=native={lib_dir}");
+            println!("cargo:rustc-link-lib={link_lib}{lua_lib}");
         }
         return Some(PathBuf::from(include_dir));
     }
@@ -72,7 +72,7 @@ pub fn probe_lua() -> Option<PathBuf> {
                 .probe(alt_probe);
         }
 
-        lua.unwrap_or_else(|_| panic!("cannot find Lua {} using `pkg-config`", ver))
+        lua.unwrap_or_else(|_| panic!("cannot find Lua {ver} using `pkg-config`"))
             .include_paths
             .get(0)
             .cloned()

mlua-sys/build/find_vendored.rs

@@ -5,22 +5,25 @@ use std::path::PathBuf;
 pub fn probe_lua() -> Option<PathBuf> {
     #[cfg(feature = "lua54")]
     let artifacts = lua_src::Build::new().build(lua_src::Lua54);
+
     #[cfg(feature = "lua53")]
     let artifacts = lua_src::Build::new().build(lua_src::Lua53);
+
     #[cfg(feature = "lua52")]
     let artifacts = lua_src::Build::new().build(lua_src::Lua52);
+
     #[cfg(feature = "lua51")]
     let artifacts = lua_src::Build::new().build(lua_src::Lua51);
+
     #[cfg(feature = "luajit")]
-    let artifacts = {
-        let mut builder = luajit_src::Build::new();
-        if cfg!(feature = "luajit52") {
-            builder.lua52compat(true);
-        }
-        builder.build()
-    };
+    let artifacts = luajit_src::Build::new()
+        .lua52compat(cfg!(feature = "luajit52"))
+        .build();
+
     #[cfg(feature = "luau")]
-    let artifacts = luau0_src::Build::new().build();
+    let artifacts = luau0_src::Build::new()
+        .enable_codegen(cfg!(feature = "luau-codegen"))
+        .build();
 
     artifacts.print_cargo_metadata();
 

mlua-sys/build/main.rs

@@ -0,0 +1,19 @@
+cfg_if::cfg_if! {
+    if #[cfg(all(feature = "lua54", not(any(feature = "lua53", feature = "lua52", feature = "lua51", feature = "luajit", feature = "luau"))))] {
+        include!("main_inner.rs");
+    } else if #[cfg(all(feature = "lua53", not(any(feature = "lua54", feature = "lua52", feature = "lua51", feature = "luajit", feature = "luau"))))] {
+        include!("main_inner.rs");
+    } else if #[cfg(all(feature = "lua52", not(any(feature = "lua54", feature = "lua53", feature = "lua51", feature = "luajit", feature = "luau"))))] {
+        include!("main_inner.rs");
+    } else if #[cfg(all(feature = "lua51", not(any(feature = "lua54", feature = "lua53", feature = "lua52", feature = "luajit", feature = "luau"))))] {
+        include!("main_inner.rs");
+    } else if #[cfg(all(feature = "luajit", not(any(feature = "lua54", feature = "lua53", feature = "lua52", feature = "lua51", feature = "luau"))))] {
+        include!("main_inner.rs");
+    } else if #[cfg(all(feature = "luau", not(any(feature = "lua54", feature = "lua53", feature = "lua52", feature = "lua51", feature = "luajit"))))] {
+        include!("main_inner.rs");
+    } else {
+        fn main() {
+            compile_error!("You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52, luau");
+        }
+    }
+}

mlua-sys/build/main_inner.rs

@@ -0,0 +1,26 @@
+cfg_if::cfg_if! {
+    if #[cfg(any(feature = "luau", feature = "vendored"))] {
+        #[path = "find_vendored.rs"]
+        mod find;
+    } else {
+        #[path = "find_normal.rs"]
+        mod find;
+    }
+}
+
+fn main() {
+    // We don't support "vendored module" mode on windows
+    #[cfg(all(feature = "vendored", feature = "module", target_os = "windows"))]
+    compile_error!(
+        "Vendored (static) builds are not supported for modules on Windows.\n"
+            + "Please, use `pkg-config` or custom mode to link to a Lua dll."
+    );
+
+    #[cfg(all(feature = "luau", feature = "module"))]
+    compile_error!("Luau does not support module mode");
+
+    #[cfg(any(not(feature = "module"), target_os = "windows"))]
+    find::probe_lua();
+
+    println!("cargo:rerun-if-changed=build");
+}

mlua-sys/src/lib.rs

@@ -1,44 +1,52 @@
-//! Low level bindings to Lua 5.4/5.3/5.2/5.1 including LuaJIT.
+//! Low level bindings to Lua 5.4/5.3/5.2/5.1 (including LuaJIT) and Roblox Luau.
 
 #![allow(non_camel_case_types, non_snake_case, dead_code)]
+#![allow(clippy::missing_safety_doc)]
+#![doc(test(attr(deny(warnings))))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 use std::os::raw::c_int;
 
-#[cfg(feature = "lua54")]
+#[cfg(any(feature = "lua54", doc))]
 pub use lua54::*;
 
-#[cfg(feature = "lua53")]
+#[cfg(any(feature = "lua53", doc))]
 pub use lua53::*;
 
-#[cfg(feature = "lua52")]
+#[cfg(any(feature = "lua52", doc))]
 pub use lua52::*;
 
-#[cfg(any(feature = "lua51", feature = "luajit"))]
+#[cfg(any(feature = "lua51", feature = "luajit", doc))]
 pub use lua51::*;
 
-#[cfg(feature = "luau")]
+#[cfg(any(feature = "luau", doc))]
 pub use luau::*;
 
 #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+#[doc(hidden)]
 pub const LUA_MAX_UPVALUES: c_int = 255;
 
 #[cfg(any(feature = "lua51", all(feature = "luajit", not(feature = "vendored"))))]
+#[doc(hidden)]
 pub const LUA_MAX_UPVALUES: c_int = 60;
 
 #[cfg(all(feature = "luajit", feature = "vendored"))]
+#[doc(hidden)]
 pub const LUA_MAX_UPVALUES: c_int = 120;
 
 #[cfg(feature = "luau")]
+#[doc(hidden)]
 pub const LUA_MAX_UPVALUES: c_int = 200;
 
 // I believe `luaL_traceback` < 5.4 requires this much free stack to not error.
 // 5.4 uses `luaL_Buffer`
+#[doc(hidden)]
 pub const LUA_TRACEBACK_STACK: c_int = 11;
 
 // The minimum alignment guaranteed by the architecture. This value is used to
 // add fast paths for low alignment values.
 // Copied from https://github.com/rust-lang/rust/blob/master/library/std/src/sys/common/alloc.rs
-#[cfg(all(any(
+#[cfg(any(
     target_arch = "x86",
     target_arch = "arm",
     target_arch = "mips",
@@ -50,9 +58,10 @@ pub const LUA_TRACEBACK_STACK: c_int = 11;
     target_arch = "hexagon",
     all(target_arch = "riscv32", not(target_os = "espidf")),
     all(target_arch = "xtensa", not(target_os = "espidf")),
-)))]
+))]
+#[doc(hidden)]
 pub const SYS_MIN_ALIGN: usize = 8;
-#[cfg(all(any(
+#[cfg(any(
     target_arch = "x86_64",
     target_arch = "aarch64",
     target_arch = "mips64",
@@ -60,44 +69,36 @@ pub const SYS_MIN_ALIGN: usize = 8;
     target_arch = "sparc64",
     target_arch = "riscv64",
     target_arch = "wasm64",
-)))]
+))]
+#[doc(hidden)]
 pub const SYS_MIN_ALIGN: usize = 16;
 // The allocator on the esp-idf platform guarentees 4 byte alignment.
-#[cfg(all(any(
+#[cfg(any(
     all(target_arch = "riscv32", target_os = "espidf"),
     all(target_arch = "xtensa", target_os = "espidf"),
-)))]
+))]
+#[doc(hidden)]
 pub const SYS_MIN_ALIGN: usize = 4;
 
-// Hack to avoid stripping a few unused Lua symbols that could be imported
-// by C modules in unsafe mode
-#[cfg(not(feature = "luau"))]
-pub(crate) fn keep_lua_symbols() {
-    let mut symbols: Vec<*const extern "C" fn()> = Vec::new();
-    symbols.push(lua_atpanic as _);
-    symbols.push(lua_isuserdata as _);
-    symbols.push(lua_tocfunction as _);
-    symbols.push(luaL_loadstring as _);
-    symbols.push(luaL_openlibs as _);
-    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
-    {
-        symbols.push(lua_getglobal as _);
-        symbols.push(lua_setglobal as _);
-        symbols.push(luaL_setfuncs as _);
-    }
-}
+#[macro_use]
+mod macros;
 
-#[cfg(feature = "lua54")]
+#[cfg(any(feature = "lua54", doc))]
+#[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
 pub mod lua54;
 
-#[cfg(feature = "lua53")]
+#[cfg(any(feature = "lua53", doc))]
+#[cfg_attr(docsrs, doc(cfg(feature = "lua53")))]
 pub mod lua53;
 
-#[cfg(feature = "lua52")]
+#[cfg(any(feature = "lua52", doc))]
+#[cfg_attr(docsrs, doc(cfg(feature = "lua52")))]
 pub mod lua52;
 
-#[cfg(any(feature = "lua51", feature = "luajit"))]
+#[cfg(any(feature = "lua51", feature = "luajit", doc))]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "lua51", feature = "luajit"))))]
 pub mod lua51;
 
-#[cfg(feature = "luau")]
+#[cfg(any(feature = "luau", doc))]
+#[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
 pub mod luau;

mlua-sys/src/lua51/compat.rs

@@ -486,10 +486,10 @@ pub unsafe fn luaL_traceback(
     lua_concat(L, lua_gettop(L) - top);
 }
 
-pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char {
+pub unsafe fn luaL_tolstring(L: *mut lua_State, mut idx: c_int, len: *mut usize) -> *const c_char {
+    idx = lua_absindex(L, idx);
     if luaL_callmeta(L, idx, cstr!("__tostring")) == 0 {
-        let t = lua_type(L, idx);
-        match t {
+        match lua_type(L, idx) {
             LUA_TNIL => {
                 lua_pushliteral(L, "nil");
             }
@@ -503,7 +503,7 @@ pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) ->
                     lua_pushliteral(L, "true");
                 }
             }
-            _ => {
+            t => {
                 let tt = luaL_getmetafield(L, idx, cstr!("__name"));
                 let name = if tt == LUA_TSTRING {
                     lua_tostring(L, -1)
@@ -512,7 +512,7 @@ pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) ->
                 };
                 lua_pushfstring(L, cstr!("%s: %p"), name, lua_topointer(L, idx));
                 if tt != LUA_TNIL {
-                    lua_replace(L, -2);
+                    lua_replace(L, -2); // remove '__name'
                 }
             }
         };

mlua-sys/src/lua52/compat.rs

@@ -205,10 +205,10 @@ pub unsafe fn luaL_newmetatable(L: *mut lua_State, tname: *const c_char) -> c_in
     }
 }
 
-pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char {
+pub unsafe fn luaL_tolstring(L: *mut lua_State, mut idx: c_int, len: *mut usize) -> *const c_char {
+    idx = lua_absindex(L, idx);
     if luaL_callmeta(L, idx, cstr!("__tostring")) == 0 {
-        let t = lua_type(L, idx);
-        match t {
+        match lua_type(L, idx) {
             LUA_TNIL => {
                 lua_pushliteral(L, "nil");
             }
@@ -222,7 +222,7 @@ pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) ->
                     lua_pushliteral(L, "true");
                 }
             }
-            _ => {
+            t => {
                 let tt = luaL_getmetafield(L, idx, cstr!("__name"));
                 let name = if tt == LUA_TSTRING {
                     lua_tostring(L, -1)
@@ -231,7 +231,7 @@ pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) ->
                 };
                 lua_pushfstring(L, cstr!("%s: %p"), name, lua_topointer(L, idx));
                 if tt != LUA_TNIL {
-                    lua_replace(L, -2);
+                    lua_replace(L, -2); // remove '__name'
                 }
             }
         };

mlua-sys/src/lua53/compat.rs

@@ -1,4 +1,4 @@
-//! MLua compatibility layer for Lua 5.2
+//! MLua compatibility layer for Lua 5.3
 
 use std::os::raw::c_int;
 

mlua-sys/src/lua53/lauxlib.rs

@@ -25,7 +25,8 @@ extern "C" {
 
     pub fn luaL_getmetafield(L: *mut lua_State, obj: c_int, e: *const c_char) -> c_int;
     pub fn luaL_callmeta(L: *mut lua_State, obj: c_int, e: *const c_char) -> c_int;
-    pub fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char;
+    #[link_name = "luaL_tolstring"]
+    pub fn luaL_tolstring_(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char;
     pub fn luaL_argerror(L: *mut lua_State, arg: c_int, extramsg: *const c_char) -> c_int;
     pub fn luaL_checklstring(L: *mut lua_State, arg: c_int, l: *mut usize) -> *const c_char;
     pub fn luaL_optlstring(
@@ -167,6 +168,11 @@ pub unsafe fn luaL_getmetatable(L: *mut lua_State, n: *const c_char) {
     lua::lua_getfield(L, lua::LUA_REGISTRYINDEX, n);
 }
 
+#[inline(always)]
+pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char {
+    luaL_tolstring_(L, lua::lua_absindex(L, idx), len)
+}
+
 // luaL_opt would be implemented here but it is undocumented, so it's omitted
 
 #[inline(always)]

mlua-sys/src/luau/compat.rs

@@ -341,7 +341,7 @@ pub unsafe fn luaL_loadbufferx(
         fn free(p: *mut c_void);
     }
 
-    let chunk_is_text = size == 0 || (*data as u8) >= b'\t';
+    let chunk_is_text = size == 0 || (*data as u8) >= b'\n';
     if !mode.is_null() {
         let modeb = CStr::from_ptr(mode).to_bytes();
         if !chunk_is_text && !modeb.contains(&b'b') {
@@ -436,10 +436,10 @@ pub unsafe fn luaL_traceback(
     lua_concat(L, lua_gettop(L) - top);
 }
 
-pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) -> *const c_char {
+pub unsafe fn luaL_tolstring(L: *mut lua_State, mut idx: c_int, len: *mut usize) -> *const c_char {
+    idx = lua_absindex(L, idx);
     if luaL_callmeta(L, idx, cstr!("__tostring")) == 0 {
-        let t = lua_type(L, idx);
-        match t {
+        match lua_type(L, idx) {
             LUA_TNIL => {
                 lua_pushliteral(L, "nil");
             }
@@ -453,7 +453,7 @@ pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) ->
                     lua_pushliteral(L, "true");
                 }
             }
-            _ => {
+            t => {
                 let tt = luaL_getmetafield(L, idx, cstr!("__name"));
                 let name = if tt == LUA_TSTRING {
                     lua_tostring(L, -1)
@@ -462,7 +462,7 @@ pub unsafe fn luaL_tolstring(L: *mut lua_State, idx: c_int, len: *mut usize) ->
                 };
                 lua_pushfstring(L, cstr!("%s: %p"), name, lua_topointer(L, idx));
                 if tt != LUA_TNIL {
-                    lua_replace(L, -2);
+                    lua_replace(L, -2); // remove '__name'
                 }
             }
         };

mlua-sys/src/luau/lua.rs

@@ -74,6 +74,7 @@ pub type lua_Continuation = unsafe extern "C" fn(L: *mut lua_State, status: c_in
 
 /// Type for userdata destructor functions.
 pub type lua_Udestructor = unsafe extern "C" fn(*mut c_void);
+pub type lua_Destructor = unsafe extern "C" fn(L: *mut lua_State, *mut c_void);
 
 /// Type for memory-allocation functions.
 pub type lua_Alloc = unsafe extern "C" fn(
@@ -83,6 +84,11 @@ pub type lua_Alloc = unsafe extern "C" fn(
     nsize: usize,
 ) -> *mut c_void;
 
+/// Returns Luau release version (eg. `0.xxx`).
+pub const fn luau_version() -> Option<&'static str> {
+    option_env!("LUAU_VERSION")
+}
+
 extern "C" {
     //
     // State manipulation
@@ -265,11 +271,8 @@ extern "C" {
     // TODO: lua_encodepointer
     pub fn lua_clock() -> c_double;
     pub fn lua_setuserdatatag(L: *mut lua_State, idx: c_int, tag: c_int);
-    pub fn lua_setuserdatadtor(
-        L: *mut lua_State,
-        tag: c_int,
-        dtor: Option<unsafe extern "C" fn(*mut lua_State, *mut c_void)>,
-    );
+    pub fn lua_setuserdatadtor(L: *mut lua_State, tag: c_int, dtor: Option<lua_Destructor>);
+    pub fn lua_getuserdatadtor(L: *mut lua_State, tag: c_int) -> Option<lua_Destructor>;
     pub fn lua_clonefunction(L: *mut lua_State, idx: c_int);
     pub fn lua_cleartable(L: *mut lua_State, idx: c_int);
 }

mlua-sys/src/luau/luacode.rs

@@ -10,8 +10,7 @@ pub struct lua_CompileOptions {
     pub coverageLevel: c_int,
     pub vectorLib: *const c_char,
     pub vectorCtor: *const c_char,
-    pub vectorType: *const c_char,
-    pub mutableGlobals: *const *const c_char,
+    pub mutableGlobals: *mut *const c_char,
 }
 
 extern "C" {

mlua-sys/src/luau/luacodegen.rs

@@ -0,0 +1,11 @@
+//! Contains definitions from `luacodegen.h`.
+
+use std::os::raw::c_int;
+
+use super::lua::lua_State;
+
+extern "C" {
+    pub fn luau_codegen_supported() -> c_int;
+    pub fn luau_codegen_create(state: *mut lua_State);
+    pub fn luau_codegen_compile(state: *mut lua_State, idx: c_int);
+}

mlua-sys/src/luau/mod.rs

@@ -4,10 +4,12 @@ pub use compat::*;
 pub use lauxlib::*;
 pub use lua::*;
 pub use luacode::*;
+pub use luacodegen::*;
 pub use lualib::*;
 
 pub mod compat;
 pub mod lauxlib;
 pub mod lua;
 pub mod luacode;
+pub mod luacodegen;
 pub mod lualib;

mlua-sys/src/macros.rs

@@ -0,0 +1,7 @@
+#[allow(unused_macros)]
+macro_rules! cstr {
+    ($s:expr) => {
+        concat!($s, "\0") as *const str as *const [::std::os::raw::c_char]
+            as *const ::std::os::raw::c_char
+    };
+}

mlua_derive/Cargo.toml

@@ -1,8 +1,8 @@
 [package]
 name = "mlua_derive"
-version = "0.8.0"
+version = "0.9.0-beta.2"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
-edition = "2018"
+edition = "2021"
 description = "Procedural macros for the mlua crate."
 repository = "https://github.com/khvzak/mlua"
 keywords = ["lua", "mlua"]
@@ -18,7 +18,7 @@ macros = ["proc-macro-error", "itertools", "regex", "once_cell"]
 quote = "1.0"
 proc-macro2 = { version = "1.0", features = ["span-locations"] }
 proc-macro-error = { version = "1.0", optional = true }
-syn = { version = "1.0", features = ["full"] }
+syn = { version = "2.0", features = ["full"] }
 itertools = { version = "0.10", optional = true }
 regex = { version = "1.4", optional = true }
 once_cell = { version = "1.0", optional = true }

mlua_derive/src/lib.rs

@@ -1,7 +1,8 @@
 use proc_macro::TokenStream;
 use proc_macro2::{Ident, Span};
 use quote::quote;
-use syn::{parse_macro_input, AttributeArgs, Error, ItemFn};
+use syn::meta::ParseNestedMeta;
+use syn::{parse_macro_input, ItemFn, LitStr, Result};
 
 #[cfg(feature = "macros")]
 use {
@@ -9,19 +10,41 @@ use {
     proc_macro_error::proc_macro_error,
 };
 
+#[derive(Default)]
+struct ModuleAttributes {
+    name: Option<Ident>,
+}
+
+impl ModuleAttributes {
+    fn parse(&mut self, meta: ParseNestedMeta) -> Result<()> {
+        if meta.path.is_ident("name") {
+            match meta.value() {
+                Ok(value) => {
+                    self.name = Some(value.parse::<LitStr>()?.parse()?);
+                }
+                Err(_) => {
+                    return Err(meta.error("`name` attribute must have a value"));
+                }
+            }
+        } else {
+            return Err(meta.error("unsupported module attribute"));
+        }
+        Ok(())
+    }
+}
+
 #[proc_macro_attribute]
 pub fn lua_module(attr: TokenStream, item: TokenStream) -> TokenStream {
-    let args = parse_macro_input!(attr as AttributeArgs);
-    let func = parse_macro_input!(item as ItemFn);
-
-    if !args.is_empty() {
-        let err = Error::new(Span::call_site(), "the macro does not support arguments")
-            .to_compile_error();
-        return err.into();
+    let mut args = ModuleAttributes::default();
+    if !attr.is_empty() {
+        let args_parser = syn::meta::parser(|meta| args.parse(meta));
+        parse_macro_input!(attr with args_parser);
     }
 
-    let func_name = func.sig.ident.clone();
-    let ext_entrypoint_name = Ident::new(&format!("luaopen_{}", func_name), Span::call_site());
+    let func = parse_macro_input!(item as ItemFn);
+    let func_name = &func.sig.ident;
+    let module_name = args.name.unwrap_or_else(|| func_name.clone());
+    let ext_entrypoint_name = Ident::new(&format!("luaopen_{module_name}"), Span::call_site());
 
     let wrapped = quote! {
         ::mlua::require_module_feature!();
@@ -61,25 +84,18 @@ pub fn chunk(input: TokenStream) -> TokenStream {
     });
 
     let wrapped_code = quote! {{
-        use ::mlua::{AsChunk, ChunkMode, Lua, Result, Value};
+        use ::mlua::{AsChunk, ChunkMode, Lua, Result, Table};
         use ::std::borrow::Cow;
         use ::std::io::Result as IoResult;
-        use ::std::marker::PhantomData;
         use ::std::sync::Mutex;
 
-        fn annotate<'a, F: FnOnce(&'a Lua) -> Result<Value<'a>>>(f: F) -> F { f }
+        struct InnerChunk<F: for <'a> FnOnce(&'a Lua) -> Result<Table<'a>>>(Mutex<Option<F>>);
 
-        struct InnerChunk<'a, F: FnOnce(&'a Lua) -> Result<Value<'a>>>(Mutex<Option<F>>, PhantomData<&'a ()>);
-
-        impl<'lua, F> AsChunk<'lua> for InnerChunk<'lua, F>
+        impl<F> AsChunk<'static> for InnerChunk<F>
         where
-            F: FnOnce(&'lua Lua) -> Result<Value<'lua>>,
+            F: for <'a> FnOnce(&'a Lua) -> Result<Table<'a>>,
         {
-            fn source(&self) -> IoResult<Cow<[u8]>> {
-                Ok(Cow::Borrowed((#source).as_bytes()))
-            }
-
-            fn env(&self, lua: &'lua Lua) -> Result<Option<Value<'lua>>> {
+            fn environment<'lua>(&self, lua: &'lua Lua) -> Result<Option<Table<'lua>>> {
                 if #caps_len > 0 {
                     if let Ok(mut make_env) = self.0.lock() {
                         if let Some(make_env) = make_env.take() {
@@ -93,9 +109,15 @@ pub fn chunk(input: TokenStream) -> TokenStream {
             fn mode(&self) -> Option<ChunkMode> {
                 Some(ChunkMode::Text)
             }
+
+            fn source(self) -> IoResult<Cow<'static, [u8]>> {
+                Ok(Cow::Borrowed((#source).as_bytes()))
+            }
         }
 
-        let make_env = annotate(move |lua: &Lua| -> Result<Value> {
+        fn annotate<F: for<'a> FnOnce(&'a Lua) -> Result<Table<'a>>>(f: F) -> F { f }
+
+        let make_env = annotate(move |lua: &Lua| -> Result<Table> {
             let globals = lua.globals();
             let env = lua.create_table()?;
             let meta = lua.create_table()?;
@@ -106,10 +128,10 @@ pub fn chunk(input: TokenStream) -> TokenStream {
             #(#caps)*
 
             env.set_metatable(Some(meta));
-            Ok(Value::Table(env))
+            Ok(env)
         });
 
-        &InnerChunk(Mutex::new(Some(make_env)), PhantomData)
+        InnerChunk(Mutex::new(Some(make_env)))
     }};
 
     wrapped_code.into()

mlua_derive/src/token.rs

@@ -59,7 +59,7 @@ fn parse_pos(span: &Span) -> Option<(usize, usize)> {
 
     static RE: Lazy<Regex> = Lazy::new(|| Regex::new(r"bytes\(([0-9]+)\.\.([0-9]+)\)").unwrap());
 
-    match RE.captures(&format!("{:?}", span)) {
+    match RE.captures(&format!("{span:?}")) {
         Some(caps) => match (caps.get(1), caps.get(2)) {
             (Some(start), Some(end)) => Some((
                 match start.as_str().parse() {

src/chunk.rs

@@ -5,23 +5,20 @@ use std::io::Result as IoResult;
 use std::path::{Path, PathBuf};
 use std::string::String as StdString;
 
-use crate::error::{Error, Result};
-use crate::ffi;
+use crate::error::{Error, ErrorContext, Result};
 use crate::function::Function;
 use crate::lua::Lua;
-use crate::value::{FromLuaMulti, ToLua, ToLuaMulti, Value};
+use crate::table::Table;
+use crate::value::{FromLuaMulti, IntoLua, IntoLuaMulti};
 
 #[cfg(feature = "async")]
-use {futures_core::future::LocalBoxFuture, futures_util::future};
+use futures_util::future::{self, LocalBoxFuture};
 
 /// Trait for types [loadable by Lua] and convertible to a [`Chunk`]
 ///
 /// [loadable by Lua]: https://www.lua.org/manual/5.4/manual.html#3.3.2
 /// [`Chunk`]: crate::Chunk
-pub trait AsChunk<'lua> {
-    /// Returns chunk data (can be text or binary)
-    fn source(&self) -> IoResult<Cow<[u8]>>;
-
+pub trait AsChunk<'a> {
     /// Returns optional chunk name
     fn name(&self) -> Option<StdString> {
         None
@@ -30,7 +27,8 @@ pub trait AsChunk<'lua> {
     /// Returns optional chunk [environment]
     ///
     /// [environment]: https://www.lua.org/manual/5.4/manual.html#2.2
-    fn env(&self, _lua: &'lua Lua) -> Result<Option<Value<'lua>>> {
+    fn environment<'lua>(&self, lua: &'lua Lua) -> Result<Option<Table<'lua>>> {
+        let _lua = lua; // suppress warning
         Ok(None)
     }
 
@@ -38,50 +36,65 @@ pub trait AsChunk<'lua> {
     fn mode(&self) -> Option<ChunkMode> {
         None
     }
+
+    /// Returns chunk data (can be text or binary)
+    fn source(self) -> IoResult<Cow<'a, [u8]>>;
 }
 
-impl<'lua> AsChunk<'lua> for str {
-    fn source(&self) -> IoResult<Cow<[u8]>> {
+impl<'a> AsChunk<'a> for &'a str {
+    fn source(self) -> IoResult<Cow<'a, [u8]>> {
         Ok(Cow::Borrowed(self.as_ref()))
     }
 }
 
-impl<'lua> AsChunk<'lua> for StdString {
-    fn source(&self) -> IoResult<Cow<[u8]>> {
+impl AsChunk<'static> for StdString {
+    fn source(self) -> IoResult<Cow<'static, [u8]>> {
+        Ok(Cow::Owned(self.into_bytes()))
+    }
+}
+
+impl<'a> AsChunk<'a> for &'a StdString {
+    fn source(self) -> IoResult<Cow<'a, [u8]>> {
+        Ok(Cow::Borrowed(self.as_bytes()))
+    }
+}
+
+impl<'a> AsChunk<'a> for &'a [u8] {
+    fn source(self) -> IoResult<Cow<'a, [u8]>> {
+        Ok(Cow::Borrowed(self))
+    }
+}
+
+impl AsChunk<'static> for Vec<u8> {
+    fn source(self) -> IoResult<Cow<'static, [u8]>> {
+        Ok(Cow::Owned(self))
+    }
+}
+
+impl<'a> AsChunk<'a> for &'a Vec<u8> {
+    fn source(self) -> IoResult<Cow<'a, [u8]>> {
         Ok(Cow::Borrowed(self.as_ref()))
     }
 }
 
-impl<'lua> AsChunk<'lua> for [u8] {
-    fn source(&self) -> IoResult<Cow<[u8]>> {
-        Ok(Cow::Borrowed(self))
-    }
-}
-
-impl<'lua> AsChunk<'lua> for Vec<u8> {
-    fn source(&self) -> IoResult<Cow<[u8]>> {
-        Ok(Cow::Borrowed(self))
-    }
-}
-
-impl<'lua> AsChunk<'lua> for Path {
-    fn source(&self) -> IoResult<Cow<[u8]>> {
-        std::fs::read(self).map(Cow::Owned)
-    }
-
+impl AsChunk<'static> for &Path {
     fn name(&self) -> Option<StdString> {
         Some(format!("@{}", self.display()))
     }
-}
 
-impl<'lua> AsChunk<'lua> for PathBuf {
-    fn source(&self) -> IoResult<Cow<[u8]>> {
+    fn source(self) -> IoResult<Cow<'static, [u8]>> {
         std::fs::read(self).map(Cow::Owned)
     }
+}
 
+impl AsChunk<'static> for PathBuf {
     fn name(&self) -> Option<StdString> {
         Some(format!("@{}", self.display()))
     }
+
+    fn source(self) -> IoResult<Cow<'static, [u8]>> {
+        std::fs::read(self).map(Cow::Owned)
+    }
 }
 
 /// Returned from [`Lua::load`] and is used to finalize loading and executing Lua main chunks.
@@ -90,10 +103,10 @@ impl<'lua> AsChunk<'lua> for PathBuf {
 #[must_use = "`Chunk`s do nothing unless one of `exec`, `eval`, `call`, or `into_function` are called on them"]
 pub struct Chunk<'lua, 'a> {
     pub(crate) lua: &'lua Lua,
-    pub(crate) source: IoResult<Cow<'a, [u8]>>,
-    pub(crate) name: Option<StdString>,
-    pub(crate) env: Result<Option<Value<'lua>>>,
+    pub(crate) name: StdString,
+    pub(crate) env: Result<Option<Table<'lua>>>,
     pub(crate) mode: Option<ChunkMode>,
+    pub(crate) source: IoResult<Cow<'a, [u8]>>,
     #[cfg(feature = "luau")]
     pub(crate) compiler: Option<Compiler>,
 }
@@ -228,7 +241,6 @@ impl Compiler {
                 coverageLevel: self.coverage_level as c_int,
                 vectorLib: vector_lib.map_or(ptr::null(), |s| s.as_ptr()),
                 vectorCtor: vector_ctor.map_or(ptr::null(), |s| s.as_ptr()),
-                vectorType: ptr::null(),
                 mutableGlobals: mutable_globals_ptr,
             };
             ffi::luau_compile(source.as_ref(), options)
@@ -238,16 +250,14 @@ impl Compiler {
 
 impl<'lua, 'a> Chunk<'lua, 'a> {
     /// Sets the name of this chunk, which results in more informative error traces.
-    pub fn set_name(mut self, name: impl AsRef<str>) -> Result<Self> {
-        self.name = Some(name.as_ref().to_string());
-        // Do extra validation
-        let _ = self.convert_name()?;
-        Ok(self)
+    pub fn set_name(mut self, name: impl Into<String>) -> Self {
+        self.name = name.into();
+        self
     }
 
-    /// Sets the first upvalue (`_ENV`) of the loaded chunk to the given value.
+    /// Sets the environment of the loaded chunk to the given value.
     ///
-    /// Lua main chunks always have exactly one upvalue, and this upvalue is used as the `_ENV`
+    /// In Lua >=5.2 main chunks always have exactly one upvalue, and this upvalue is used as the `_ENV`
     /// variable inside the chunk. By default this value is set to the global environment.
     ///
     /// Calling this method changes the `_ENV` upvalue to the value provided, and variables inside
@@ -256,10 +266,12 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     /// All global variables (including the standard library!) are looked up in `_ENV`, so it may be
     /// necessary to populate the environment in order for scripts using custom environments to be
     /// useful.
-    pub fn set_environment<V: ToLua<'lua>>(mut self, env: V) -> Result<Self> {
-        // Prefer to propagate errors here and wrap to `Ok`
-        self.env = Ok(Some(env.to_lua(self.lua)?));
-        Ok(self)
+    pub fn set_environment<V: IntoLua<'lua>>(mut self, env: V) -> Self {
+        self.env = env
+            .into_lua(self.lua)
+            .and_then(|val| self.lua.unpack(val))
+            .context("bad environment value");
+        self
     }
 
     /// Sets whether the chunk is text or binary (autodetected by default).
@@ -300,10 +312,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     /// [`exec`]: #method.exec
     #[cfg(feature = "async")]
     #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
-    pub fn exec_async<'fut>(self) -> LocalBoxFuture<'fut, Result<()>>
-    where
-        'lua: 'fut,
-    {
+    pub fn exec_async(self) -> LocalBoxFuture<'lua, Result<()>> {
         self.call_async(())
     }
 
@@ -352,7 +361,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     /// Load the chunk function and call it with the given arguments.
     ///
     /// This is equivalent to `into_function` and calling the resulting function.
-    pub fn call<A: ToLuaMulti<'lua>, R: FromLuaMulti<'lua>>(self, args: A) -> Result<R> {
+    pub fn call<A: IntoLuaMulti<'lua>, R: FromLuaMulti<'lua>>(self, args: A) -> Result<R> {
         self.into_function()?.call(args)
     }
 
@@ -368,7 +377,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     pub fn call_async<'fut, A, R>(self, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut,
     {
         match self.into_function() {
@@ -388,9 +397,9 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
             self.compile();
         }
 
-        let name = self.convert_name()?;
+        let name = Self::convert_name(self.name)?;
         self.lua
-            .load_chunk(self.source?.as_ref(), name.as_deref(), self.env?, self.mode)
+            .load_chunk(Some(&name), self.env?, self.mode, self.source?.as_ref())
     }
 
     /// Compiles the chunk and changes mode to binary.
@@ -409,7 +418,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
                     self.mode = Some(ChunkMode::Binary);
                 }
                 #[cfg(not(feature = "luau"))]
-                if let Ok(func) = self.lua.load_chunk(source.as_ref(), None, None, None) {
+                if let Ok(func) = self.lua.load_chunk(None, None, None, source.as_ref()) {
                     let data = func.dump(false);
                     self.source = Ok(Cow::Owned(data));
                     self.mode = Some(ChunkMode::Binary);
@@ -449,7 +458,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
                     } else {
                         let mut cache = ChunksCache(HashMap::new());
                         cache.0.insert(text_source, binary_source.as_ref().to_vec());
-                        self.lua.set_app_data(cache);
+                        let _ = self.lua.try_set_app_data(cache);
                     }
                 }
             }
@@ -471,9 +480,9 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
             .map(|c| c.compile(&source))
             .unwrap_or(source);
 
-        let name = self.convert_name()?;
+        let name = Self::convert_name(self.name.clone())?;
         self.lua
-            .load_chunk(&source, name.as_deref(), self.env.clone()?, None)
+            .load_chunk(Some(&name), self.env.clone()?, None, &source)
     }
 
     fn detect_mode(&self) -> ChunkMode {
@@ -494,12 +503,8 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
         }
     }
 
-    fn convert_name(&self) -> Result<Option<CString>> {
-        self.name
-            .clone()
-            .map(CString::new)
-            .transpose()
-            .map_err(|err| Error::RuntimeError(format!("invalid name: {err}")))
+    fn convert_name(name: String) -> Result<CString> {
+        CString::new(name).map_err(|err| Error::RuntimeError(format!("invalid name: {err}")))
     }
 
     fn expression_source(source: &[u8]) -> Vec<u8> {

src/conversion.rs

@@ -1,5 +1,3 @@
-#![allow(clippy::wrong_self_convention)]
-
 use std::borrow::Cow;
 use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::convert::TryInto;
@@ -11,18 +9,24 @@ use bstr::{BStr, BString};
 use num_traits::cast;
 
 use crate::error::{Error, Result};
-use crate::function::Function;
+use crate::function::{Function, WrappedFunction};
 use crate::lua::Lua;
 use crate::string::String;
 use crate::table::Table;
 use crate::thread::Thread;
 use crate::types::{LightUserData, MaybeSend};
-use crate::userdata::{AnyUserData, UserData};
-use crate::value::{FromLua, Nil, ToLua, Value};
+use crate::userdata::{AnyUserData, UserData, UserDataRef, UserDataRefMut};
+use crate::value::{FromLua, IntoLua, Nil, Value};
 
-impl<'lua> ToLua<'lua> for Value<'lua> {
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+use crate::{function::OwnedFunction, table::OwnedTable, userdata::OwnedAnyUserData};
+
+#[cfg(feature = "async")]
+use crate::function::WrappedAsyncFunction;
+
+impl<'lua> IntoLua<'lua> for Value<'lua> {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(self)
     }
 }
@@ -34,9 +38,9 @@ impl<'lua> FromLua<'lua> for Value<'lua> {
     }
 }
 
-impl<'lua> ToLua<'lua> for String<'lua> {
+impl<'lua> IntoLua<'lua> for String<'lua> {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(self))
     }
 }
@@ -54,9 +58,9 @@ impl<'lua> FromLua<'lua> for String<'lua> {
     }
 }
 
-impl<'lua> ToLua<'lua> for Table<'lua> {
+impl<'lua> IntoLua<'lua> for Table<'lua> {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(self))
     }
 }
@@ -75,9 +79,27 @@ impl<'lua> FromLua<'lua> for Table<'lua> {
     }
 }
 
-impl<'lua> ToLua<'lua> for Function<'lua> {
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for OwnedTable {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Table(Table(lua.adopt_owned_ref(self.0))))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> FromLua<'lua> for OwnedTable {
+    #[inline]
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<OwnedTable> {
+        Table::from_lua(value, lua).map(|s| s.into_owned())
+    }
+}
+
+impl<'lua> IntoLua<'lua> for Function<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Function(self))
     }
 }
@@ -96,9 +118,42 @@ impl<'lua> FromLua<'lua> for Function<'lua> {
     }
 }
 
-impl<'lua> ToLua<'lua> for Thread<'lua> {
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for OwnedFunction {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Function(Function(lua.adopt_owned_ref(self.0))))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> FromLua<'lua> for OwnedFunction {
+    #[inline]
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<OwnedFunction> {
+        Function::from_lua(value, lua).map(|s| s.into_owned())
+    }
+}
+
+impl<'lua> IntoLua<'lua> for WrappedFunction<'lua> {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        lua.create_callback(self.0).map(Value::Function)
+    }
+}
+
+#[cfg(feature = "async")]
+impl<'lua> IntoLua<'lua> for WrappedAsyncFunction<'lua> {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        lua.create_async_callback(self.0).map(Value::Function)
+    }
+}
+
+impl<'lua> IntoLua<'lua> for Thread<'lua> {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Thread(self))
     }
 }
@@ -117,9 +172,9 @@ impl<'lua> FromLua<'lua> for Thread<'lua> {
     }
 }
 
-impl<'lua> ToLua<'lua> for AnyUserData<'lua> {
+impl<'lua> IntoLua<'lua> for AnyUserData<'lua> {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::UserData(self))
     }
 }
@@ -138,30 +193,48 @@ impl<'lua> FromLua<'lua> for AnyUserData<'lua> {
     }
 }
 
-impl<'lua, T: 'static + MaybeSend + UserData> ToLua<'lua> for T {
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> IntoLua<'lua> for OwnedAnyUserData {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::UserData(AnyUserData(lua.adopt_owned_ref(self.0))))
+    }
+}
+
+#[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+#[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+impl<'lua> FromLua<'lua> for OwnedAnyUserData {
+    #[inline]
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<OwnedAnyUserData> {
+        AnyUserData::from_lua(value, lua).map(|s| s.into_owned())
+    }
+}
+
+impl<'lua, T: 'static + MaybeSend + UserData> IntoLua<'lua> for T {
+    #[inline]
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::UserData(lua.create_userdata(self)?))
     }
 }
 
-impl<'lua, T: 'static + UserData + Clone> FromLua<'lua> for T {
+impl<'lua, T: 'static> FromLua<'lua> for UserDataRef<'lua, T> {
     #[inline]
-    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<T> {
-        match value {
-            Value::UserData(ud) => Ok(ud.borrow::<T>()?.clone()),
-            _ => Err(Error::FromLuaConversionError {
-                from: value.type_name(),
-                to: "userdata",
-                message: None,
-            }),
-        }
+    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
+        Self::from_value(value)
     }
 }
 
-impl<'lua> ToLua<'lua> for Error {
+impl<'lua, T: 'static> FromLua<'lua> for UserDataRefMut<'lua, T> {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
+        Self::from_value(value)
+    }
+}
+
+impl<'lua> IntoLua<'lua> for Error {
+    #[inline]
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Error(self))
     }
 }
@@ -180,9 +253,9 @@ impl<'lua> FromLua<'lua> for Error {
     }
 }
 
-impl<'lua> ToLua<'lua> for bool {
+impl<'lua> IntoLua<'lua> for bool {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Boolean(self))
     }
 }
@@ -198,9 +271,9 @@ impl<'lua> FromLua<'lua> for bool {
     }
 }
 
-impl<'lua> ToLua<'lua> for LightUserData {
+impl<'lua> IntoLua<'lua> for LightUserData {
     #[inline]
-    fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::LightUserData(self))
     }
 }
@@ -219,9 +292,9 @@ impl<'lua> FromLua<'lua> for LightUserData {
     }
 }
 
-impl<'lua> ToLua<'lua> for StdString {
+impl<'lua> IntoLua<'lua> for StdString {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(&self)?))
     }
 }
@@ -242,23 +315,23 @@ impl<'lua> FromLua<'lua> for StdString {
     }
 }
 
-impl<'lua> ToLua<'lua> for &str {
+impl<'lua> IntoLua<'lua> for &str {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(self)?))
     }
 }
 
-impl<'lua> ToLua<'lua> for Cow<'_, str> {
+impl<'lua> IntoLua<'lua> for Cow<'_, str> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(self.as_bytes())?))
     }
 }
 
-impl<'lua> ToLua<'lua> for Box<str> {
+impl<'lua> IntoLua<'lua> for Box<str> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(&*self)?))
     }
 }
@@ -280,9 +353,9 @@ impl<'lua> FromLua<'lua> for Box<str> {
     }
 }
 
-impl<'lua> ToLua<'lua> for CString {
+impl<'lua> IntoLua<'lua> for CString {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(self.as_bytes())?))
     }
 }
@@ -310,23 +383,23 @@ impl<'lua> FromLua<'lua> for CString {
     }
 }
 
-impl<'lua> ToLua<'lua> for &CStr {
+impl<'lua> IntoLua<'lua> for &CStr {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(self.to_bytes())?))
     }
 }
 
-impl<'lua> ToLua<'lua> for Cow<'_, CStr> {
+impl<'lua> IntoLua<'lua> for Cow<'_, CStr> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(self.to_bytes())?))
     }
 }
 
-impl<'lua> ToLua<'lua> for BString {
+impl<'lua> IntoLua<'lua> for BString {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(&self)?))
     }
 }
@@ -348,18 +421,18 @@ impl<'lua> FromLua<'lua> for BString {
     }
 }
 
-impl<'lua> ToLua<'lua> for &BStr {
+impl<'lua> IntoLua<'lua> for &BStr {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::String(lua.create_string(self)?))
     }
 }
 
 macro_rules! lua_convert_int {
     ($x:ty) => {
-        impl<'lua> ToLua<'lua> for $x {
+        impl<'lua> IntoLua<'lua> for $x {
             #[inline]
-            fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+            fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
                 cast(self)
                     .map(Value::Integer)
                     .or_else(|| cast(self).map(Value::Number))
@@ -420,9 +493,9 @@ lua_convert_int!(usize);
 
 macro_rules! lua_convert_float {
     ($x:ty) => {
-        impl<'lua> ToLua<'lua> for $x {
+        impl<'lua> IntoLua<'lua> for $x {
             #[inline]
-            fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
+            fn into_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
                 cast(self)
                     .ok_or_else(|| Error::ToLuaConversionError {
                         from: stringify!($x),
@@ -458,24 +531,24 @@ macro_rules! lua_convert_float {
 lua_convert_float!(f32);
 lua_convert_float!(f64);
 
-impl<'lua, T> ToLua<'lua> for &[T]
+impl<'lua, T> IntoLua<'lua> for &[T]
 where
-    T: Clone + ToLua<'lua>,
+    T: Clone + IntoLua<'lua>,
 {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(
             lua.create_sequence_from(self.iter().cloned())?,
         ))
     }
 }
 
-impl<'lua, T, const N: usize> ToLua<'lua> for [T; N]
+impl<'lua, T, const N: usize> IntoLua<'lua> for [T; N]
 where
-    T: ToLua<'lua>,
+    T: IntoLua<'lua>,
 {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_sequence_from(self)?))
     }
 }
@@ -516,9 +589,9 @@ where
     }
 }
 
-impl<'lua, T: ToLua<'lua>> ToLua<'lua> for Box<[T]> {
+impl<'lua, T: IntoLua<'lua>> IntoLua<'lua> for Box<[T]> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_sequence_from(self.into_vec())?))
     }
 }
@@ -530,9 +603,9 @@ impl<'lua, T: FromLua<'lua>> FromLua<'lua> for Box<[T]> {
     }
 }
 
-impl<'lua, T: ToLua<'lua>> ToLua<'lua> for Vec<T> {
+impl<'lua, T: IntoLua<'lua>> IntoLua<'lua> for Vec<T> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_sequence_from(self)?))
     }
 }
@@ -557,11 +630,11 @@ impl<'lua, T: FromLua<'lua>> FromLua<'lua> for Vec<T> {
     }
 }
 
-impl<'lua, K: Eq + Hash + ToLua<'lua>, V: ToLua<'lua>, S: BuildHasher> ToLua<'lua>
+impl<'lua, K: Eq + Hash + IntoLua<'lua>, V: IntoLua<'lua>, S: BuildHasher> IntoLua<'lua>
     for HashMap<K, V, S>
 {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_table_from(self)?))
     }
 }
@@ -583,9 +656,9 @@ impl<'lua, K: Eq + Hash + FromLua<'lua>, V: FromLua<'lua>, S: BuildHasher + Defa
     }
 }
 
-impl<'lua, K: Ord + ToLua<'lua>, V: ToLua<'lua>> ToLua<'lua> for BTreeMap<K, V> {
+impl<'lua, K: Ord + IntoLua<'lua>, V: IntoLua<'lua>> IntoLua<'lua> for BTreeMap<K, V> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_table_from(self)?))
     }
 }
@@ -605,9 +678,9 @@ impl<'lua, K: Ord + FromLua<'lua>, V: FromLua<'lua>> FromLua<'lua> for BTreeMap<
     }
 }
 
-impl<'lua, T: Eq + Hash + ToLua<'lua>, S: BuildHasher> ToLua<'lua> for HashSet<T, S> {
+impl<'lua, T: Eq + Hash + IntoLua<'lua>, S: BuildHasher> IntoLua<'lua> for HashSet<T, S> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_table_from(
             self.into_iter().map(|val| (val, true)),
         )?))
@@ -632,9 +705,9 @@ impl<'lua, T: Eq + Hash + FromLua<'lua>, S: BuildHasher + Default> FromLua<'lua>
     }
 }
 
-impl<'lua, T: Ord + ToLua<'lua>> ToLua<'lua> for BTreeSet<T> {
+impl<'lua, T: Ord + IntoLua<'lua>> IntoLua<'lua> for BTreeSet<T> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         Ok(Value::Table(lua.create_table_from(
             self.into_iter().map(|val| (val, true)),
         )?))
@@ -659,11 +732,11 @@ impl<'lua, T: Ord + FromLua<'lua>> FromLua<'lua> for BTreeSet<T> {
     }
 }
 
-impl<'lua, T: ToLua<'lua>> ToLua<'lua> for Option<T> {
+impl<'lua, T: IntoLua<'lua>> IntoLua<'lua> for Option<T> {
     #[inline]
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         match self {
-            Some(val) => val.to_lua(lua),
+            Some(val) => val.into_lua(lua),
             None => Ok(Nil),
         }
     }

src/error.rs

@@ -1,5 +1,3 @@
-#![allow(clippy::wrong_self_convention)]
-
 use std::error::Error as StdError;
 use std::fmt;
 use std::io::Error as IoError;
@@ -9,6 +7,8 @@ use std::str::Utf8Error;
 use std::string::String as StdString;
 use std::sync::Arc;
 
+use crate::private::Sealed;
+
 /// Error type returned by `mlua` methods.
 #[derive(Debug, Clone)]
 #[non_exhaustive]
@@ -71,6 +71,20 @@ pub enum Error {
     StackError,
     /// Too many arguments to `Function::bind`
     BindError,
+    /// Bad argument received from Lua (usually when calling a function).
+    ///
+    /// This error can help to identify the argument that caused the error
+    /// (which is stored in the corresponding field).
+    BadArgument {
+        /// Function that was called.
+        to: Option<StdString>,
+        /// Argument position (usually starts from 1).
+        pos: usize,
+        /// Argument name.
+        name: Option<StdString>,
+        /// Underlying error returned when converting argument to a Lua value.
+        cause: Arc<Error>,
+    },
     /// A Rust value could not be converted to a Lua value.
     ToLuaConversionError {
         /// Name of the Rust type that could not be converted.
@@ -142,8 +156,11 @@ pub enum Error {
     ///
     /// [`MetaMethod`]: crate::MetaMethod
     MetaMethodTypeError {
+        /// Name of the metamethod.
         method: StdString,
+        /// Passed value type.
         type_name: &'static str,
+        /// A string containing more detailed error information.
         message: Option<StdString>,
     },
     /// A [`RegistryKey`] produced from a different Lua state was used.
@@ -178,6 +195,13 @@ pub enum Error {
     /// error. The Rust code that originally invoked the Lua code then receives a `CallbackError`,
     /// from which the original error (and a stack traceback) can be recovered.
     ExternalError(Arc<dyn StdError + Send + Sync>),
+    /// An error with additional context.
+    WithContext {
+        /// A string containing additional context.
+        context: StdString,
+        /// Underlying error.
+        cause: Arc<Error>,
+    },
 }
 
 /// A specialized `Result` type used by `mlua`'s API.
@@ -187,17 +211,17 @@ pub type Result<T> = StdResult<T, Error>;
 impl fmt::Display for Error {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Error::SyntaxError { ref message, .. } => write!(fmt, "syntax error: {}", message),
-            Error::RuntimeError(ref msg) => write!(fmt, "runtime error: {}", msg),
+            Error::SyntaxError { ref message, .. } => write!(fmt, "syntax error: {message}"),
+            Error::RuntimeError(ref msg) => write!(fmt, "runtime error: {msg}"),
             Error::MemoryError(ref msg) => {
-                write!(fmt, "memory error: {}", msg)
+                write!(fmt, "memory error: {msg}")
             }
             #[cfg(any(feature = "lua53", feature = "lua52"))]
             Error::GarbageCollectorError(ref msg) => {
-                write!(fmt, "garbage collector error: {}", msg)
+                write!(fmt, "garbage collector error: {msg}")
             }
             Error::SafetyError(ref msg) => {
-                write!(fmt, "safety error: {}", msg)
+                write!(fmt, "safety error: {msg}")
             },
             Error::MemoryLimitNotAvailable => {
                 write!(fmt, "setting memory limit is not available")
@@ -218,18 +242,29 @@ impl fmt::Display for Error {
                 fmt,
                 "too many arguments to Function::bind"
             ),
+            Error::BadArgument { ref to, pos, ref name, ref cause } => {
+                if let Some(name) = name {
+                    write!(fmt, "bad argument `{name}`")?;
+                } else {
+                    write!(fmt, "bad argument #{pos}")?;
+                }
+                if let Some(to) = to {
+                    write!(fmt, " to `{to}`")?;
+                }
+                write!(fmt, ": {cause}")
+            },
             Error::ToLuaConversionError { from, to, ref message } => {
-                write!(fmt, "error converting {} to Lua {}", from, to)?;
+                write!(fmt, "error converting {from} to Lua {to}")?;
                 match *message {
                     None => Ok(()),
-                    Some(ref message) => write!(fmt, " ({})", message),
+                    Some(ref message) => write!(fmt, " ({message})"),
                 }
             }
             Error::FromLuaConversionError { from, to, ref message } => {
-                write!(fmt, "error converting Lua {} to {}", from, to)?;
+                write!(fmt, "error converting Lua {from} to {to}")?;
                 match *message {
                     None => Ok(()),
-                    Some(ref message) => write!(fmt, " ({})", message),
+                    Some(ref message) => write!(fmt, " ({message})"),
                 }
             }
             Error::CoroutineInactive => write!(fmt, "cannot resume inactive coroutine"),
@@ -237,25 +272,25 @@ impl fmt::Display for Error {
             Error::UserDataDestructed => write!(fmt, "userdata has been destructed"),
             Error::UserDataBorrowError => write!(fmt, "userdata already mutably borrowed"),
             Error::UserDataBorrowMutError => write!(fmt, "userdata already borrowed"),
-            Error::MetaMethodRestricted(ref method) => write!(fmt, "metamethod {} is restricted", method),
+            Error::MetaMethodRestricted(ref method) => write!(fmt, "metamethod {method} is restricted"),
             Error::MetaMethodTypeError { ref method, type_name, ref message } => {
-                write!(fmt, "metamethod {} has unsupported type {}", method, type_name)?;
+                write!(fmt, "metamethod {method} has unsupported type {type_name}")?;
                 match *message {
                     None => Ok(()),
-                    Some(ref message) => write!(fmt, " ({})", message),
+                    Some(ref message) => write!(fmt, " ({message})"),
                 }
             }
             Error::MismatchedRegistryKey => {
                 write!(fmt, "RegistryKey used from different Lua state")
             }
             Error::CallbackError { ref cause, ref traceback } => {
-                writeln!(fmt, "callback error")?;
                 // Trace errors down to the root
                 let (mut cause, mut full_traceback) = (cause, None);
                 while let Error::CallbackError { cause: ref cause2, traceback: ref traceback2 } = **cause {
                     cause = cause2;
                     full_traceback = Some(traceback2);
                 }
+                writeln!(fmt, "{cause}")?;
                 if let Some(full_traceback) = full_traceback {
                     let traceback = traceback.trim_start_matches("stack traceback:");
                     let traceback = traceback.trim_start().trim_end();
@@ -269,20 +304,24 @@ impl fmt::Display for Error {
                 } else {
                     writeln!(fmt, "{}", traceback.trim_end())?;
                 }
-                write!(fmt, "caused by: {}", cause)
+                Ok(())
             }
             Error::PreviouslyResumedPanic => {
                 write!(fmt, "previously resumed panic returned again")
             }
             #[cfg(feature = "serialize")]
             Error::SerializeError(ref err) => {
-                write!(fmt, "serialize error: {}", err)
+                write!(fmt, "serialize error: {err}")
             },
             #[cfg(feature = "serialize")]
             Error::DeserializeError(ref err) => {
-                write!(fmt, "deserialize error: {}", err)
+                write!(fmt, "deserialize error: {err}")
             },
-            Error::ExternalError(ref err) => write!(fmt, "{}", err),
+            Error::ExternalError(ref err) => write!(fmt, "{err}"),
+            Error::WithContext { ref context, ref cause } => {
+                writeln!(fmt, "{context}")?;
+                write!(fmt, "{cause}")
+            }
         }
     }
 }
@@ -296,53 +335,138 @@ impl StdError for Error {
             // Given that we include source to fmt::Display implementation for `CallbackError`, this call returns nothing.
             Error::CallbackError { .. } => None,
             Error::ExternalError(ref err) => err.source(),
+            Error::WithContext { ref cause, .. } => match cause.as_ref() {
+                Error::ExternalError(err) => err.source(),
+                _ => None,
+            },
             _ => None,
         }
     }
 }
 
 impl Error {
-    pub fn external<T: Into<Box<dyn StdError + Send + Sync>>>(err: T) -> Error {
+    /// Wraps an external error object.
+    pub fn external<T: Into<Box<dyn StdError + Send + Sync>>>(err: T) -> Self {
         Error::ExternalError(err.into().into())
     }
+
+    /// Attempts to downcast the external error object to a concrete type by reference.
+    pub fn downcast_ref<T>(&self) -> Option<&T>
+    where
+        T: StdError + 'static,
+    {
+        match self {
+            Error::ExternalError(err) => err.downcast_ref(),
+            Error::WithContext { cause, .. } => match cause.as_ref() {
+                Error::ExternalError(err) => err.downcast_ref(),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+
+    pub(crate) fn bad_self_argument(to: &str, cause: Error) -> Self {
+        Error::BadArgument {
+            to: Some(to.to_string()),
+            pos: 1,
+            name: Some("self".to_string()),
+            cause: Arc::new(cause),
+        }
+    }
+
+    pub(crate) fn from_lua_conversion<'a>(
+        from: &'static str,
+        to: &'static str,
+        message: impl Into<Option<&'a str>>,
+    ) -> Self {
+        Error::FromLuaConversionError {
+            from,
+            to,
+            message: message.into().map(|s| s.into()),
+        }
+    }
 }
 
 pub trait ExternalError {
-    fn to_lua_err(self) -> Error;
+    fn into_lua_err(self) -> Error;
 }
 
 impl<E: Into<Box<dyn StdError + Send + Sync>>> ExternalError for E {
-    fn to_lua_err(self) -> Error {
+    fn into_lua_err(self) -> Error {
         Error::external(self)
     }
 }
 
 pub trait ExternalResult<T> {
-    fn to_lua_err(self) -> Result<T>;
+    fn into_lua_err(self) -> Result<T>;
 }
 
 impl<T, E> ExternalResult<T> for StdResult<T, E>
 where
     E: ExternalError,
 {
-    fn to_lua_err(self) -> Result<T> {
-        self.map_err(|e| e.to_lua_err())
+    fn into_lua_err(self) -> Result<T> {
+        self.map_err(|e| e.into_lua_err())
     }
 }
 
-impl std::convert::From<AddrParseError> for Error {
+/// Provides the `context` method for [`Error`] and `Result<T, Error>`.
+pub trait ErrorContext: Sealed {
+    /// Wraps the error value with additional context.
+    fn context<C: fmt::Display>(self, context: C) -> Self;
+
+    /// Wrap the error value with additional context that is evaluated lazily
+    /// only once an error does occur.
+    fn with_context<C: fmt::Display>(self, f: impl FnOnce(&Error) -> C) -> Self;
+}
+
+impl ErrorContext for Error {
+    fn context<C: fmt::Display>(self, context: C) -> Self {
+        let context = context.to_string();
+        match self {
+            Error::WithContext { cause, .. } => Error::WithContext { context, cause },
+            _ => Error::WithContext {
+                context,
+                cause: Arc::new(self),
+            },
+        }
+    }
+
+    fn with_context<C: fmt::Display>(self, f: impl FnOnce(&Error) -> C) -> Self {
+        let context = f(&self).to_string();
+        match self {
+            Error::WithContext { cause, .. } => Error::WithContext { context, cause },
+            _ => Error::WithContext {
+                context,
+                cause: Arc::new(self),
+            },
+        }
+    }
+}
+
+impl<T> ErrorContext for StdResult<T, Error> {
+    fn context<C: fmt::Display>(self, context: C) -> Self {
+        self.map_err(|err| err.context(context))
+    }
+
+    fn with_context<C: fmt::Display>(self, f: impl FnOnce(&Error) -> C) -> Self {
+        self.map_err(|err| err.with_context(f))
+    }
+}
+
+impl From<AddrParseError> for Error {
     fn from(err: AddrParseError) -> Self {
         Error::external(err)
     }
 }
 
-impl std::convert::From<IoError> for Error {
+impl From<IoError> for Error {
     fn from(err: IoError) -> Self {
         Error::external(err)
     }
 }
 
-impl std::convert::From<Utf8Error> for Error {
+impl From<Utf8Error> for Error {
     fn from(err: Utf8Error) -> Self {
         Error::external(err)
     }

src/function.rs

@@ -1,32 +1,74 @@
+use std::cell::RefCell;
 use std::mem;
 use std::os::raw::{c_int, c_void};
 use std::ptr;
 use std::slice;
 
 use crate::error::{Error, Result};
-use crate::ffi;
-use crate::types::LuaRef;
+use crate::lua::Lua;
+use crate::memory::MemoryState;
+use crate::table::Table;
+use crate::types::{Callback, LuaRef, MaybeSend};
 use crate::util::{
     assert_stack, check_stack, error_traceback, pop_error, ptr_to_cstr_bytes, StackGuard,
 };
-use crate::value::{FromLuaMulti, ToLuaMulti};
+use crate::value::{FromLuaMulti, IntoLua, IntoLuaMulti};
 
 #[cfg(feature = "async")]
-use {futures_core::future::LocalBoxFuture, futures_util::future};
+use {
+    crate::types::AsyncCallback,
+    futures_util::future::{self, Future, LocalBoxFuture, TryFutureExt},
+};
 
 /// Handle to an internal Lua function.
 #[derive(Clone, Debug)]
 pub struct Function<'lua>(pub(crate) LuaRef<'lua>);
 
+/// Owned handle to an internal Lua function.
+///
+/// The owned handle holds a *strong* reference to the current Lua instance.
+/// Be warned, if you place it into a Lua type (eg. [`UserData`] or a Rust callback), it is *very easy*
+/// to accidentally cause reference cycles that would prevent destroying Lua instance.
+///
+/// [`UserData`]: crate::UserData
+#[cfg(feature = "unstable")]
+#[cfg_attr(docsrs, doc(cfg(feature = "unstable")))]
+#[derive(Clone, Debug)]
+pub struct OwnedFunction(pub(crate) crate::types::LuaOwnedRef);
+
+#[cfg(feature = "unstable")]
+impl OwnedFunction {
+    /// Get borrowed handle to the underlying Lua function.
+    #[cfg_attr(feature = "send", allow(unused))]
+    pub const fn to_ref(&self) -> Function {
+        Function(self.0.to_ref())
+    }
+}
+
+/// Contains information about a function.
+///
+/// Please refer to the [`Lua Debug Interface`] for more information.
+///
+/// [`Lua Debug Interface`]: https://www.lua.org/manual/5.4/manual.html#4.7
 #[derive(Clone, Debug)]
 pub struct FunctionInfo {
-    pub name: Option<Vec<u8>>,
-    pub name_what: Option<Vec<u8>>,
-    pub what: Option<Vec<u8>>,
+    /// A (reasonable) name of the function.
+    pub name: Option<String>,
+    /// Explains the `name` field ("global", "local", "method", "field", "upvalue", or "").
+    ///
+    /// Always `None` for Luau.
+    pub name_what: Option<String>,
+    /// A string "Lua" if the function is a Lua function, "C" if it is a C function, "main" if it is the main part of a chunk.
+    pub what: Option<String>,
+    /// The source of the chunk that created the function.
     pub source: Option<Vec<u8>>,
+    /// A "printable" version of source, to be used in error messages.
     pub short_src: Option<Vec<u8>>,
+    /// The line number where the definition of the function starts.
     pub line_defined: i32,
-    #[cfg(not(feature = "luau"))]
+    /// The line number where the definition of the function ends.
+    ///
+    /// Always `-1` for Luau.
     pub last_line_defined: i32,
 }
 
@@ -82,33 +124,34 @@ impl<'lua> Function<'lua> {
     /// # Ok(())
     /// # }
     /// ```
-    pub fn call<A: ToLuaMulti<'lua>, R: FromLuaMulti<'lua>>(&self, args: A) -> Result<R> {
+    pub fn call<A: IntoLuaMulti<'lua>, R: FromLuaMulti<'lua>>(&self, args: A) -> Result<R> {
         let lua = self.0.lua;
+        let state = lua.state();
 
-        let mut args = args.to_lua_multi(lua)?;
+        let mut args = args.into_lua_multi(lua)?;
         let nargs = args.len() as c_int;
 
         let results = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, nargs + 3)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, nargs + 3)?;
 
-            ffi::lua_pushcfunction(lua.state, error_traceback);
-            let stack_start = ffi::lua_gettop(lua.state);
+            MemoryState::relax_limit_with(state, || ffi::lua_pushcfunction(state, error_traceback));
+            let stack_start = ffi::lua_gettop(state);
             lua.push_ref(&self.0);
             for arg in args.drain_all() {
                 lua.push_value(arg)?;
             }
-            let ret = ffi::lua_pcall(lua.state, nargs, ffi::LUA_MULTRET, stack_start);
+            let ret = ffi::lua_pcall(state, nargs, ffi::LUA_MULTRET, stack_start);
             if ret != ffi::LUA_OK {
-                return Err(pop_error(lua.state, ret));
+                return Err(pop_error(state, ret));
             }
-            let nresults = ffi::lua_gettop(lua.state) - stack_start;
+            let nresults = ffi::lua_gettop(state) - stack_start;
             let mut results = args; // Reuse MultiValue container
-            assert_stack(lua.state, 2);
+            assert_stack(state, 2);
             for _ in 0..nresults {
                 results.push_front(lua.pop_value());
             }
-            ffi::lua_pop(lua.state, 1);
+            ffi::lua_pop(state, 1);
             results
         };
         R::from_lua_multi(results, lua)
@@ -148,11 +191,11 @@ impl<'lua> Function<'lua> {
     pub fn call_async<'fut, A, R>(&self, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut,
     {
         let lua = self.0.lua;
-        match lua.create_recycled_thread(self.clone()) {
+        match lua.create_recycled_thread(self) {
             Ok(t) => {
                 let mut t = t.into_async(args);
                 t.set_recyclable(true);
@@ -189,7 +232,7 @@ impl<'lua> Function<'lua> {
     /// # Ok(())
     /// # }
     /// ```
-    pub fn bind<A: ToLuaMulti<'lua>>(&self, args: A) -> Result<Function<'lua>> {
+    pub fn bind<A: IntoLuaMulti<'lua>>(&self, args: A) -> Result<Function<'lua>> {
         unsafe extern "C" fn args_wrapper_impl(state: *mut ffi::lua_State) -> c_int {
             let nargs = ffi::lua_gettop(state);
             let nbinds = ffi::lua_tointeger(state, ffi::lua_upvalueindex(1)) as c_int;
@@ -206,8 +249,9 @@ impl<'lua> Function<'lua> {
         }
 
         let lua = self.0.lua;
+        let state = lua.state();
 
-        let args = args.to_lua_multi(lua)?;
+        let args = args.into_lua_multi(lua)?;
         let nargs = args.len() as c_int;
 
         if nargs == 0 {
@@ -219,14 +263,14 @@ impl<'lua> Function<'lua> {
         }
 
         let args_wrapper = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, nargs + 3)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, nargs + 3)?;
 
-            ffi::lua_pushinteger(lua.state, nargs as ffi::lua_Integer);
+            ffi::lua_pushinteger(state, nargs as ffi::lua_Integer);
             for arg in args {
                 lua.push_value(arg)?;
             }
-            protect_lua!(lua.state, nargs + 1, 1, fn(state) {
+            protect_lua!(state, nargs + 1, 1, fn(state) {
                 ffi::lua_pushcclosure(state, args_wrapper_impl, ffi::lua_gettop(state));
             })?;
 
@@ -242,10 +286,113 @@ impl<'lua> Function<'lua> {
             "#,
         )
         .try_cache()
-        .set_name("_mlua_bind")?
+        .set_name("__mlua_bind")
         .call((self.clone(), args_wrapper))
     }
 
+    /// Returns the environment of the Lua function.
+    ///
+    /// By default Lua functions shares a global environment.
+    ///
+    /// This function always returns `None` for Rust/C functions.
+    pub fn environment(&self) -> Option<Table> {
+        let lua = self.0.lua;
+        let state = lua.state();
+        unsafe {
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 1);
+
+            lua.push_ref(&self.0);
+
+            let mut ar: ffi::lua_Debug = mem::zeroed();
+            #[cfg(not(feature = "luau"))]
+            {
+                ffi::lua_pushvalue(state, -1);
+                ffi::lua_getinfo(state, cstr!(">S"), &mut ar);
+            }
+            #[cfg(feature = "luau")]
+            ffi::lua_getinfo(state, -1, cstr!("s"), &mut ar);
+
+            if ptr_to_cstr_bytes(ar.what) == Some(b"C") {
+                return None;
+            }
+
+            #[cfg(any(feature = "lua51", feature = "luajit", feature = "luau"))]
+            ffi::lua_getfenv(state, -1);
+            #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+            for i in 1..=255 {
+                // Traverse upvalues until we find the _ENV one
+                match ffi::lua_getupvalue(state, -1, i) {
+                    s if s.is_null() => break,
+                    s if std::ffi::CStr::from_ptr(s as _).to_bytes() == b"_ENV" => break,
+                    _ => ffi::lua_pop(state, 1),
+                }
+            }
+
+            if ffi::lua_type(state, -1) != ffi::LUA_TTABLE {
+                return None;
+            }
+            Some(Table(lua.pop_ref()))
+        }
+    }
+
+    /// Sets the environment of the Lua function.
+    ///
+    /// The environment is a table that is used as the global environment for the function.
+    /// Returns `true` if environment successfully changed, `false` otherwise.
+    ///
+    /// This function does nothing for Rust/C functions.
+    pub fn set_environment(&self, env: Table) -> Result<bool> {
+        let lua = self.0.lua;
+        let state = lua.state();
+        unsafe {
+            let _sg = StackGuard::new(state);
+            check_stack(state, 2)?;
+
+            lua.push_ref(&self.0);
+
+            let mut ar: ffi::lua_Debug = mem::zeroed();
+            #[cfg(not(feature = "luau"))]
+            {
+                ffi::lua_pushvalue(state, -1);
+                ffi::lua_getinfo(state, cstr!(">S"), &mut ar);
+            }
+            #[cfg(feature = "luau")]
+            ffi::lua_getinfo(state, -1, cstr!("s"), &mut ar);
+
+            if ptr_to_cstr_bytes(ar.what) == Some(b"C") {
+                return Ok(false);
+            }
+
+            #[cfg(any(feature = "lua51", feature = "luajit", feature = "luau"))]
+            {
+                lua.push_ref(&env.0);
+                ffi::lua_setfenv(state, -2);
+            }
+            #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+            for i in 1..=255 {
+                match ffi::lua_getupvalue(state, -1, i) {
+                    s if s.is_null() => return Ok(false),
+                    s if std::ffi::CStr::from_ptr(s as _).to_bytes() == b"_ENV" => {
+                        ffi::lua_pop(state, 1);
+                        // Create an anonymous function with the new environment
+                        let f_with_env = lua
+                            .load("return _ENV")
+                            .set_environment(env)
+                            .try_cache()
+                            .into_function()?;
+                        lua.push_ref(&f_with_env.0);
+                        ffi::lua_upvaluejoin(state, -2, i, -1, 1);
+                        break;
+                    }
+                    _ => ffi::lua_pop(state, 1),
+                }
+            }
+
+            Ok(true)
+        }
+    }
+
     /// Returns information about the function.
     ///
     /// Corresponds to the `>Sn` what mask for [`lua_getinfo`] when applied to the function.
@@ -253,25 +400,27 @@ impl<'lua> Function<'lua> {
     /// [`lua_getinfo`]: https://www.lua.org/manual/5.4/manual.html#lua_getinfo
     pub fn info(&self) -> FunctionInfo {
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 1);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 1);
 
             let mut ar: ffi::lua_Debug = mem::zeroed();
             lua.push_ref(&self.0);
             #[cfg(not(feature = "luau"))]
-            let res = ffi::lua_getinfo(lua.state, cstr!(">Sn"), &mut ar);
+            let res = ffi::lua_getinfo(state, cstr!(">Sn"), &mut ar);
             #[cfg(feature = "luau")]
-            let res = ffi::lua_getinfo(lua.state, -1, cstr!("sn"), &mut ar);
+            let res = ffi::lua_getinfo(state, -1, cstr!("sn"), &mut ar);
             mlua_assert!(res != 0, "lua_getinfo failed with `>Sn`");
 
             FunctionInfo {
-                name: ptr_to_cstr_bytes(ar.name).map(|s| s.to_vec()),
+                name: ptr_to_cstr_bytes(ar.name).map(|s| String::from_utf8_lossy(s).into_owned()),
                 #[cfg(not(feature = "luau"))]
-                name_what: ptr_to_cstr_bytes(ar.namewhat).map(|s| s.to_vec()),
+                name_what: ptr_to_cstr_bytes(ar.namewhat)
+                    .map(|s| String::from_utf8_lossy(s).into_owned()),
                 #[cfg(feature = "luau")]
                 name_what: None,
-                what: ptr_to_cstr_bytes(ar.what).map(|s| s.to_vec()),
+                what: ptr_to_cstr_bytes(ar.what).map(|s| String::from_utf8_lossy(s).into_owned()),
                 source: ptr_to_cstr_bytes(ar.source).map(|s| s.to_vec()),
                 #[cfg(not(feature = "luau"))]
                 short_src: ptr_to_cstr_bytes(ar.short_src.as_ptr()).map(|s| s.to_vec()),
@@ -280,6 +429,8 @@ impl<'lua> Function<'lua> {
                 line_defined: ar.linedefined,
                 #[cfg(not(feature = "luau"))]
                 last_line_defined: ar.lastlinedefined,
+                #[cfg(feature = "luau")]
+                last_line_defined: -1,
             }
         }
     }
@@ -308,15 +459,16 @@ impl<'lua> Function<'lua> {
         }
 
         let lua = self.0.lua;
+        let state = lua.state();
         let mut data: Vec<u8> = Vec::new();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 1);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 1);
 
             lua.push_ref(&self.0);
             let data_ptr = &mut data as *mut Vec<u8> as *mut c_void;
-            ffi::lua_dump(lua.state, writer, data_ptr, strip as i32);
-            ffi::lua_pop(lua.state, 1);
+            ffi::lua_dump(state, writer, data_ptr, strip as i32);
+            ffi::lua_pop(state, 1);
         }
 
         data
@@ -364,15 +516,24 @@ impl<'lua> Function<'lua> {
         }
 
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 1);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 1);
 
             lua.push_ref(&self.0);
             let func_ptr = &mut func as *mut F as *mut c_void;
-            ffi::lua_getcoverage(lua.state, -1, func_ptr, callback::<F>);
+            ffi::lua_getcoverage(state, -1, func_ptr, callback::<F>);
         }
     }
+
+    /// Convert this handle to owned version.
+    #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+    #[inline]
+    pub fn into_owned(self) -> OwnedFunction {
+        OwnedFunction(self.0.into_owned())
+    }
 }
 
 impl<'lua> PartialEq for Function<'lua> {
@@ -380,3 +541,100 @@ impl<'lua> PartialEq for Function<'lua> {
         self.0 == other.0
     }
 }
+
+// Additional shortcuts
+#[cfg(feature = "unstable")]
+impl OwnedFunction {
+    /// Calls the function, passing `args` as function arguments.
+    ///
+    /// This is a shortcut for [`Function::call()`].
+    #[inline]
+    pub fn call<'lua, A, R>(&'lua self, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>,
+    {
+        self.to_ref().call(args)
+    }
+
+    /// Returns a future that, when polled, calls `self`, passing `args` as function arguments,
+    /// and drives the execution.
+    ///
+    /// This is a shortcut for [`Function::call_async()`].
+    #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    #[inline]
+    pub fn call_async<'lua, A, R>(&'lua self, args: A) -> LocalBoxFuture<'lua, Result<R>>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'lua,
+    {
+        self.to_ref().call_async(args)
+    }
+}
+
+pub(crate) struct WrappedFunction<'lua>(pub(crate) Callback<'lua, 'static>);
+
+#[cfg(feature = "async")]
+pub(crate) struct WrappedAsyncFunction<'lua>(pub(crate) AsyncCallback<'lua, 'static>);
+
+impl<'lua> Function<'lua> {
+    /// Wraps a Rust function or closure, returning an opaque type that implements [`IntoLua`] trait.
+    #[inline]
+    pub fn wrap<A, R, F>(func: F) -> impl IntoLua<'lua>
+    where
+        A: FromLuaMulti<'lua>,
+        R: IntoLuaMulti<'lua>,
+        F: Fn(&'lua Lua, A) -> Result<R> + MaybeSend + 'static,
+    {
+        WrappedFunction(Box::new(move |lua, args| {
+            func(lua, A::from_lua_multi(args, lua)?)?.into_lua_multi(lua)
+        }))
+    }
+
+    /// Wraps a Rust mutable closure, returning an opaque type that implements [`IntoLua`] trait.
+    #[inline]
+    pub fn wrap_mut<A, R, F>(func: F) -> impl IntoLua<'lua>
+    where
+        A: FromLuaMulti<'lua>,
+        R: IntoLuaMulti<'lua>,
+        F: FnMut(&'lua Lua, A) -> Result<R> + MaybeSend + 'static,
+    {
+        let func = RefCell::new(func);
+        WrappedFunction(Box::new(move |lua, args| {
+            let mut func = func
+                .try_borrow_mut()
+                .map_err(|_| Error::RecursiveMutCallback)?;
+            func(lua, A::from_lua_multi(args, lua)?)?.into_lua_multi(lua)
+        }))
+    }
+
+    /// Wraps a Rust async function or closure, returning an opaque type that implements [`IntoLua`] trait.
+    #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    pub fn wrap_async<A, R, F, FR>(func: F) -> impl IntoLua<'lua>
+    where
+        A: FromLuaMulti<'lua>,
+        R: IntoLuaMulti<'lua>,
+        F: Fn(&'lua Lua, A) -> FR + MaybeSend + 'static,
+        FR: Future<Output = Result<R>> + 'lua,
+    {
+        WrappedAsyncFunction(Box::new(move |lua, args| {
+            let args = match A::from_lua_multi(args, lua) {
+                Ok(args) => args,
+                Err(e) => return Box::pin(future::err(e)),
+            };
+            Box::pin(func(lua, args).and_then(move |ret| future::ready(ret.into_lua_multi(lua))))
+        }))
+    }
+}
+
+#[cfg(test)]
+mod assertions {
+    use super::*;
+
+    static_assertions::assert_not_impl_any!(Function: Send);
+
+    #[cfg(all(feature = "unstable", not(feature = "send")))]
+    static_assertions::assert_not_impl_any!(OwnedFunction: Send);
+}

src/hook.rs

@@ -3,7 +3,8 @@ use std::cell::UnsafeCell;
 use std::ops::{BitOr, BitOrAssign};
 use std::os::raw::c_int;
 
-use crate::ffi::{self, lua_Debug};
+use ffi::lua_Debug;
+
 use crate::lua::Lua;
 use crate::util::ptr_to_cstr_bytes;
 
@@ -67,12 +68,12 @@ impl<'lua> Debug<'lua> {
         unsafe {
             #[cfg(not(feature = "luau"))]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, cstr!("n"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), cstr!("n"), self.ar.get()) != 0,
                 "lua_getinfo failed with `n`"
             );
             #[cfg(feature = "luau")]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, self.level, cstr!("n"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), self.level, cstr!("n"), self.ar.get()) != 0,
                 "lua_getinfo failed with `n`"
             );
 
@@ -91,12 +92,12 @@ impl<'lua> Debug<'lua> {
         unsafe {
             #[cfg(not(feature = "luau"))]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, cstr!("S"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), cstr!("S"), self.ar.get()) != 0,
                 "lua_getinfo failed with `S`"
             );
             #[cfg(feature = "luau")]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, self.level, cstr!("s"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), self.level, cstr!("s"), self.ar.get()) != 0,
                 "lua_getinfo failed with `s`"
             );
 
@@ -119,12 +120,12 @@ impl<'lua> Debug<'lua> {
         unsafe {
             #[cfg(not(feature = "luau"))]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, cstr!("l"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), cstr!("l"), self.ar.get()) != 0,
                 "lua_getinfo failed with `l`"
             );
             #[cfg(feature = "luau")]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, self.level, cstr!("l"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), self.level, cstr!("l"), self.ar.get()) != 0,
                 "lua_getinfo failed with `l`"
             );
 
@@ -139,7 +140,7 @@ impl<'lua> Debug<'lua> {
     pub fn is_tail_call(&self) -> bool {
         unsafe {
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, cstr!("t"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), cstr!("t"), self.ar.get()) != 0,
                 "lua_getinfo failed with `t`"
             );
             (*self.ar.get()).currentline != 0
@@ -151,20 +152,20 @@ impl<'lua> Debug<'lua> {
         unsafe {
             #[cfg(not(feature = "luau"))]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, cstr!("u"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), cstr!("u"), self.ar.get()) != 0,
                 "lua_getinfo failed with `u`"
             );
             #[cfg(feature = "luau")]
             mlua_assert!(
-                ffi::lua_getinfo(self.lua.state, self.level, cstr!("a"), self.ar.get()) != 0,
+                ffi::lua_getinfo(self.lua.state(), self.level, cstr!("a"), self.ar.get()) != 0,
                 "lua_getinfo failed with `a`"
             );
 
             #[cfg(not(feature = "luau"))]
             let stack = DebugStack {
-                num_ups: (*self.ar.get()).nups as i32,
+                num_ups: (*self.ar.get()).nups as _,
                 #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
-                num_params: (*self.ar.get()).nparams as i32,
+                num_params: (*self.ar.get()).nparams as _,
                 #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
                 is_vararg: (*self.ar.get()).isvararg != 0,
             };
@@ -266,48 +267,59 @@ pub struct HookTriggers {
 
 #[cfg(not(feature = "luau"))]
 impl HookTriggers {
-    /// Returns a new instance of `HookTriggers` with [`on_calls`] trigger set.
+    /// An instance of `HookTriggers` with `on_calls` trigger set.
+    pub const ON_CALLS: Self = HookTriggers::new().on_calls();
+
+    /// An instance of `HookTriggers` with `on_returns` trigger set.
+    pub const ON_RETURNS: Self = HookTriggers::new().on_returns();
+
+    /// An instance of `HookTriggers` with `every_line` trigger set.
+    pub const EVERY_LINE: Self = HookTriggers::new().every_line();
+
+    /// Returns a new instance of `HookTriggers` with all triggers disabled.
+    pub const fn new() -> Self {
+        HookTriggers {
+            on_calls: false,
+            on_returns: false,
+            every_line: false,
+            every_nth_instruction: None,
+        }
+    }
+
+    /// Returns an instance of `HookTriggers` with [`on_calls`] trigger set.
     ///
     /// [`on_calls`]: #structfield.on_calls
-    pub fn on_calls() -> Self {
-        HookTriggers {
-            on_calls: true,
-            ..Default::default()
-        }
+    pub const fn on_calls(mut self) -> Self {
+        self.on_calls = true;
+        self
     }
 
-    /// Returns a new instance of `HookTriggers` with [`on_returns`] trigger set.
+    /// Returns an instance of `HookTriggers` with [`on_returns`] trigger set.
     ///
     /// [`on_returns`]: #structfield.on_returns
-    pub fn on_returns() -> Self {
-        HookTriggers {
-            on_returns: true,
-            ..Default::default()
-        }
+    pub const fn on_returns(mut self) -> Self {
+        self.on_returns = true;
+        self
     }
 
-    /// Returns a new instance of `HookTriggers` with [`every_line`] trigger set.
+    /// Returns an instance of `HookTriggers` with [`every_line`] trigger set.
     ///
     /// [`every_line`]: #structfield.every_line
-    pub fn every_line() -> Self {
-        HookTriggers {
-            every_line: true,
-            ..Default::default()
-        }
+    pub const fn every_line(mut self) -> Self {
+        self.every_line = true;
+        self
     }
 
-    /// Returns a new instance of `HookTriggers` with [`every_nth_instruction`] trigger set.
+    /// Returns an instance of `HookTriggers` with [`every_nth_instruction`] trigger set.
     ///
     /// [`every_nth_instruction`]: #structfield.every_nth_instruction
-    pub fn every_nth_instruction(n: u32) -> Self {
-        HookTriggers {
-            every_nth_instruction: Some(n),
-            ..Default::default()
-        }
+    pub const fn every_nth_instruction(mut self, n: u32) -> Self {
+        self.every_nth_instruction = Some(n);
+        self
     }
 
     // Compute the mask to pass to `lua_sethook`.
-    pub(crate) fn mask(&self) -> c_int {
+    pub(crate) const fn mask(&self) -> c_int {
         let mut mask: c_int = 0;
         if self.on_calls {
             mask |= ffi::LUA_MASKCALL
@@ -326,8 +338,9 @@ impl HookTriggers {
 
     // Returns the `count` parameter to pass to `lua_sethook`, if applicable. Otherwise, zero is
     // returned.
-    pub(crate) fn count(&self) -> c_int {
-        self.every_nth_instruction.unwrap_or(0) as c_int
+    pub(crate) const fn count(&self) -> c_int {
+        let Some(n) = self.every_nth_instruction else { return 0 };
+        n as c_int
     }
 }
 

src/lib.rs

@@ -10,10 +10,10 @@
 //!
 //! # Converting data
 //!
-//! The [`ToLua`] and [`FromLua`] traits allow conversion from Rust types to Lua values and vice
+//! The [`IntoLua`] and [`FromLua`] traits allow conversion from Rust types to Lua values and vice
 //! versa. They are implemented for many data structures found in Rust's standard library.
 //!
-//! For more general conversions, the [`ToLuaMulti`] and [`FromLuaMulti`] traits allow converting
+//! For more general conversions, the [`IntoLuaMulti`] and [`FromLuaMulti`] traits allow converting
 //! between Rust types and *any number* of Lua values.
 //!
 //! Most code in `mlua` is generic over implementors of those traits, so in most places the normal
@@ -54,9 +54,9 @@
 //! [executing]: crate::Chunk::exec
 //! [evaluating]: crate::Chunk::eval
 //! [globals]: crate::Lua::globals
-//! [`ToLua`]: crate::ToLua
+//! [`IntoLua`]: crate::IntoLua
 //! [`FromLua`]: crate::FromLua
-//! [`ToLuaMulti`]: crate::ToLuaMulti
+//! [`IntoLuaMulti`]: crate::IntoLuaMulti
 //! [`FromLuaMulti`]: crate::FromLuaMulti
 //! [`Function`]: crate::Function
 //! [`UserData`]: crate::UserData
@@ -82,12 +82,12 @@ mod macros;
 mod chunk;
 mod conversion;
 mod error;
-mod ffi;
 mod function;
 mod hook;
 mod lua;
 #[cfg(feature = "luau")]
 mod luau;
+mod memory;
 mod multi;
 mod scope;
 mod stdlib;
@@ -96,16 +96,17 @@ mod table;
 mod thread;
 mod types;
 mod userdata;
+mod userdata_ext;
 mod userdata_impl;
 mod util;
 mod value;
 
 pub mod prelude;
 
-pub use crate::{ffi::lua_CFunction, ffi::lua_State};
+pub use ffi::{lua_CFunction, lua_State};
 
 pub use crate::chunk::{AsChunk, Chunk, ChunkMode};
-pub use crate::error::{Error, ExternalError, ExternalResult, Result};
+pub use crate::error::{Error, ErrorContext, ExternalError, ExternalResult, Result};
 pub use crate::function::{Function, FunctionInfo};
 pub use crate::hook::{Debug, DebugEvent, DebugNames, DebugSource, DebugStack};
 pub use crate::lua::{GCMode, Lua, LuaOptions};
@@ -115,11 +116,14 @@ pub use crate::stdlib::StdLib;
 pub use crate::string::String;
 pub use crate::table::{Table, TableExt, TablePairs, TableSequence};
 pub use crate::thread::{Thread, ThreadStatus};
-pub use crate::types::{Integer, LightUserData, Number, RegistryKey};
+pub use crate::types::{AppDataRef, AppDataRefMut, Integer, LightUserData, Number, RegistryKey};
 pub use crate::userdata::{
     AnyUserData, MetaMethod, UserData, UserDataFields, UserDataMetatable, UserDataMethods,
+    UserDataRef, UserDataRefMut,
 };
-pub use crate::value::{FromLua, FromLuaMulti, MultiValue, Nil, ToLua, ToLuaMulti, Value};
+pub use crate::userdata_ext::AnyUserDataExt;
+pub use crate::userdata_impl::UserDataRegistrar;
+pub use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, MultiValue, Nil, Value};
 
 #[cfg(not(feature = "luau"))]
 pub use crate::hook::HookTriggers;
@@ -141,17 +145,23 @@ pub use crate::serde::{
 #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
 pub mod serde;
 
-#[cfg(any(feature = "mlua_derive"))]
+#[cfg(feature = "mlua_derive")]
 #[allow(unused_imports)]
 #[macro_use]
 extern crate mlua_derive;
 
+// Unstable features
+#[cfg(feature = "unstable")]
+pub use crate::{
+    function::OwnedFunction, string::OwnedString, table::OwnedTable, userdata::OwnedAnyUserData,
+};
+
 /// Create a type that implements [`AsChunk`] and can capture Rust variables.
 ///
 /// This macro allows to write Lua code directly in Rust code.
 ///
 /// Rust variables can be referenced from Lua using `$` prefix, as shown in the example below.
-/// User's Rust types needs to implement [`UserData`] or [`ToLua`] traits.
+/// User's Rust types needs to implement [`UserData`] or [`IntoLua`] traits.
 ///
 /// Captured variables are **moved** into the chunk.
 ///
@@ -197,8 +207,8 @@ extern crate mlua_derive;
 ///
 /// [`AsChunk`]: crate::AsChunk
 /// [`UserData`]: crate::UserData
-/// [`ToLua`]: crate::ToLua
-#[cfg(any(feature = "macros"))]
+/// [`IntoLua`]: crate::IntoLua
+#[cfg(feature = "macros")]
 #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
 pub use mlua_derive::chunk;
 
@@ -219,6 +229,29 @@ pub use mlua_derive::chunk;
 ///
 /// Internally in the code above the compiler defines C function `luaopen_my_module`.
 ///
+/// You can also pass options to the attribute:
+///
+/// name - name of the module, defaults to the name of the function
+///
+/// ```ignore
+/// #[mlua::lua_module(name = "alt_module")]
+/// fn my_module(lua: &Lua) -> Result<Table> {
+///     ...
+/// }
+/// ```
+///
 #[cfg(any(feature = "module", docsrs))]
 #[cfg_attr(docsrs, doc(cfg(feature = "module")))]
 pub use mlua_derive::lua_module;
+
+pub(crate) mod private {
+    use super::*;
+
+    pub trait Sealed {}
+
+    impl Sealed for Error {}
+    impl<T> Sealed for std::result::Result<T, Error> {}
+    impl Sealed for Lua {}
+    impl Sealed for Table<'_> {}
+    impl Sealed for AnyUserData<'_> {}
+}

src/luau.rs

@@ -1,9 +1,9 @@
 use std::ffi::CStr;
 use std::os::raw::{c_float, c_int};
+use std::string::String as StdString;
 
 use crate::chunk::ChunkMode;
 use crate::error::{Error, Result};
-use crate::ffi;
 use crate::lua::Lua;
 use crate::table::Table;
 use crate::util::{check_stack, StackGuard};
@@ -24,7 +24,7 @@ impl Lua {
 
         // Set `_VERSION` global to include version number
         // The environment variable `LUAU_VERSION` set by the build script
-        if let Some(version) = option_env!("LUAU_VERSION") {
+        if let Some(version) = ffi::luau_version() {
             globals.raw_set("_VERSION", format!("Luau {version}"))?;
         }
 
@@ -69,14 +69,15 @@ unsafe extern "C" fn lua_collectgarbage(state: *mut ffi::lua_State) -> c_int {
     }
 }
 
-fn lua_require(lua: &Lua, name: Option<std::string::String>) -> Result<Value> {
+fn lua_require(lua: &Lua, name: Option<StdString>) -> Result<Value> {
     let name = name.ok_or_else(|| Error::RuntimeError("invalid module name".into()))?;
 
     // Find module in the cache
+    let state = lua.state();
     let loaded = unsafe {
-        let _sg = StackGuard::new(lua.state);
-        check_stack(lua.state, 2)?;
-        protect_lua!(lua.state, 0, 1, fn(state) {
+        let _sg = StackGuard::new(state);
+        check_stack(state, 2)?;
+        protect_lua!(state, 0, 1, fn(state) {
             ffi::luaL_getsubtable(state, ffi::LUA_REGISTRYINDEX, cstr!("_LOADED"));
         })?;
         Table(lua.pop_ref())
@@ -100,11 +101,11 @@ fn lua_require(lua: &Lua, name: Option<std::string::String>) -> Result<Value> {
             break;
         }
     }
-    let source = source.ok_or_else(|| Error::RuntimeError(format!("cannot find '{}'", name)))?;
+    let source = source.ok_or_else(|| Error::RuntimeError(format!("cannot find '{name}'")))?;
 
     let value = lua
         .load(&source)
-        .set_name(&format!("={}", source_name))?
+        .set_name(&format!("={source_name}"))
         .set_mode(ChunkMode::Text)
         .call::<_, Value>(())?;
 

src/macros.rs

@@ -103,7 +103,12 @@ macro_rules! protect_lua {
     ($state:expr, $nargs:expr, $nresults:expr, fn($state_inner:ident) $code:expr) => {{
         unsafe extern "C" fn do_call($state_inner: *mut ffi::lua_State) -> ::std::os::raw::c_int {
             $code;
-            $nresults
+            let nresults = $nresults;
+            if nresults == ::ffi::LUA_MULTRET {
+                ffi::lua_gettop($state_inner)
+            } else {
+                nresults
+            }
         }
 
         crate::util::protect_lua_call($state, $nargs, do_call)

src/memory.rs

@@ -0,0 +1,152 @@
+use std::alloc::{self, Layout};
+use std::os::raw::c_void;
+use std::ptr;
+
+#[cfg(feature = "luau")]
+use crate::lua::ExtraData;
+
+pub(crate) static ALLOCATOR: ffi::lua_Alloc = allocator;
+
+#[derive(Default)]
+pub(crate) struct MemoryState {
+    used_memory: isize,
+    memory_limit: isize,
+    // Can be set to temporary ignore the memory limit.
+    // This is used when calling `lua_pushcfunction` for lua5.1/jit/luau.
+    ignore_limit: bool,
+    // Indicates that the memory limit was reached on the last allocation.
+    #[cfg(feature = "luau")]
+    limit_reached: bool,
+}
+
+impl MemoryState {
+    #[inline]
+    pub(crate) fn used_memory(&self) -> usize {
+        self.used_memory as usize
+    }
+
+    #[inline]
+    pub(crate) fn memory_limit(&self) -> usize {
+        self.memory_limit as usize
+    }
+
+    #[inline]
+    pub(crate) fn set_memory_limit(&mut self, limit: usize) -> usize {
+        let prev_limit = self.memory_limit;
+        self.memory_limit = limit as isize;
+        prev_limit as usize
+    }
+
+    // This function is used primarily for calling `lua_pushcfunction` in lua5.1/jit
+    // to bypass the memory limit (if set).
+    #[cfg(any(feature = "lua51", feature = "luajit"))]
+    #[inline]
+    pub(crate) unsafe fn relax_limit_with(state: *mut ffi::lua_State, f: impl FnOnce()) {
+        let mut mem_state: *mut c_void = ptr::null_mut();
+        if ffi::lua_getallocf(state, &mut mem_state) == ALLOCATOR {
+            (*(mem_state as *mut MemoryState)).ignore_limit = true;
+            f();
+            (*(mem_state as *mut MemoryState)).ignore_limit = false;
+        } else {
+            f();
+        }
+    }
+
+    // Same as the above but for Luau
+    // It does not have `lua_getallocf` function, so instead we use `lua_callbacks`
+    #[cfg(feature = "luau")]
+    #[inline]
+    pub(crate) unsafe fn relax_limit_with(state: *mut ffi::lua_State, f: impl FnOnce()) {
+        let extra = (*ffi::lua_callbacks(state)).userdata as *mut ExtraData;
+        if extra.is_null() {
+            return f();
+        }
+        let mem_state = (*extra).mem_state();
+        (*mem_state.as_ptr()).ignore_limit = true;
+        f();
+        (*mem_state.as_ptr()).ignore_limit = false;
+    }
+
+    // Does nothing apart from calling `f()`, we don't need to bypass any limits
+    #[cfg(any(feature = "lua52", feature = "lua53", feature = "lua54"))]
+    #[inline]
+    pub(crate) unsafe fn relax_limit_with(_state: *mut ffi::lua_State, f: impl FnOnce()) {
+        f();
+    }
+
+    // Returns `true` if the memory limit was reached on the last memory operation
+    #[cfg(feature = "luau")]
+    pub(crate) unsafe fn limit_reached(state: *mut ffi::lua_State) -> bool {
+        let extra = (*ffi::lua_callbacks(state)).userdata as *mut ExtraData;
+        if extra.is_null() {
+            return false;
+        }
+        (*(*extra).mem_state().as_ptr()).limit_reached
+    }
+}
+
+unsafe extern "C" fn allocator(
+    extra: *mut c_void,
+    ptr: *mut c_void,
+    osize: usize,
+    nsize: usize,
+) -> *mut c_void {
+    let mem_state = &mut *(extra as *mut MemoryState);
+    #[cfg(feature = "luau")]
+    {
+        // Reset the flag
+        mem_state.limit_reached = false;
+    }
+
+    if nsize == 0 {
+        // Free memory
+        if !ptr.is_null() {
+            let layout = Layout::from_size_align_unchecked(osize, ffi::SYS_MIN_ALIGN);
+            alloc::dealloc(ptr as *mut u8, layout);
+            mem_state.used_memory -= osize as isize;
+        }
+        return ptr::null_mut();
+    }
+
+    // Do not allocate more than isize::MAX
+    if nsize > isize::MAX as usize {
+        return ptr::null_mut();
+    }
+
+    // Are we fit to the memory limits?
+    let mut mem_diff = nsize as isize;
+    if !ptr.is_null() {
+        mem_diff -= osize as isize;
+    }
+    let mem_limit = mem_state.memory_limit;
+    let new_used_memory = mem_state.used_memory + mem_diff;
+    if mem_limit > 0 && new_used_memory > mem_limit && !mem_state.ignore_limit {
+        #[cfg(feature = "luau")]
+        {
+            mem_state.limit_reached = true;
+        }
+        return ptr::null_mut();
+    }
+    mem_state.used_memory += mem_diff;
+
+    if ptr.is_null() {
+        // Allocate new memory
+        let new_layout = match Layout::from_size_align(nsize, ffi::SYS_MIN_ALIGN) {
+            Ok(layout) => layout,
+            Err(_) => return ptr::null_mut(),
+        };
+        let new_ptr = alloc::alloc(new_layout) as *mut c_void;
+        if new_ptr.is_null() {
+            alloc::handle_alloc_error(new_layout);
+        }
+        return new_ptr;
+    }
+
+    // Reallocate memory
+    let old_layout = Layout::from_size_align_unchecked(osize, ffi::SYS_MIN_ALIGN);
+    let new_ptr = alloc::realloc(ptr as *mut u8, old_layout, nsize) as *mut c_void;
+    if new_ptr.is_null() {
+        alloc::handle_alloc_error(old_layout);
+    }
+    new_ptr
+}

src/multi.rs

@@ -1,23 +1,21 @@
-#![allow(clippy::wrong_self_convention)]
-
 use std::iter::FromIterator;
 use std::ops::{Deref, DerefMut};
 use std::result::Result as StdResult;
 
 use crate::error::Result;
 use crate::lua::Lua;
-use crate::value::{FromLua, FromLuaMulti, MultiValue, Nil, ToLua, ToLuaMulti};
+use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, MultiValue, Nil};
 
 /// Result is convertible to `MultiValue` following the common Lua idiom of returning the result
 /// on success, or in the case of an error, returning `nil` and an error message.
-impl<'lua, T: ToLua<'lua>, E: ToLua<'lua>> ToLuaMulti<'lua> for StdResult<T, E> {
+impl<'lua, T: IntoLua<'lua>, E: IntoLua<'lua>> IntoLuaMulti<'lua> for StdResult<T, E> {
     #[inline]
-    fn to_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
-        let mut result = MultiValue::new_or_cached(lua);
+    fn into_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
+        let mut result = MultiValue::new_or_pooled(lua);
         match self {
-            Ok(v) => result.push_front(v.to_lua(lua)?),
+            Ok(v) => result.push_front(v.into_lua(lua)?),
             Err(e) => {
-                result.push_front(e.to_lua(lua)?);
+                result.push_front(e.into_lua(lua)?);
                 result.push_front(Nil);
             }
         }
@@ -25,11 +23,11 @@ impl<'lua, T: ToLua<'lua>, E: ToLua<'lua>> ToLuaMulti<'lua> for StdResult<T, E>
     }
 }
 
-impl<'lua, T: ToLua<'lua>> ToLuaMulti<'lua> for T {
+impl<'lua, T: IntoLua<'lua>> IntoLuaMulti<'lua> for T {
     #[inline]
-    fn to_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
-        let mut v = MultiValue::new_or_cached(lua);
-        v.push_front(self.to_lua(lua)?);
+    fn into_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
+        let mut v = MultiValue::new_or_pooled(lua);
+        v.push_front(self.into_lua(lua)?);
         Ok(v)
     }
 }
@@ -38,14 +36,26 @@ impl<'lua, T: FromLua<'lua>> FromLuaMulti<'lua> for T {
     #[inline]
     fn from_lua_multi(mut values: MultiValue<'lua>, lua: &'lua Lua) -> Result<Self> {
         let res = T::from_lua(values.pop_front().unwrap_or(Nil), lua);
-        lua.cache_multivalue(values);
+        MultiValue::return_to_pool(values, lua);
+        res
+    }
+
+    #[inline]
+    fn from_lua_multi_args(
+        mut values: MultiValue<'lua>,
+        i: usize,
+        to: Option<&str>,
+        lua: &'lua Lua,
+    ) -> Result<Self> {
+        let res = T::from_lua_arg(values.pop_front().unwrap_or(Nil), i, to, lua);
+        MultiValue::return_to_pool(values, lua);
         res
     }
 }
 
-impl<'lua> ToLuaMulti<'lua> for MultiValue<'lua> {
+impl<'lua> IntoLuaMulti<'lua> for MultiValue<'lua> {
     #[inline]
-    fn to_lua_multi(self, _: &'lua Lua) -> Result<MultiValue<'lua>> {
+    fn into_lua_multi(self, _: &'lua Lua) -> Result<MultiValue<'lua>> {
         Ok(self)
     }
 }
@@ -128,11 +138,11 @@ impl<T> DerefMut for Variadic<T> {
     }
 }
 
-impl<'lua, T: ToLua<'lua>> ToLuaMulti<'lua> for Variadic<T> {
+impl<'lua, T: IntoLua<'lua>> IntoLuaMulti<'lua> for Variadic<T> {
     #[inline]
-    fn to_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
-        let mut values = MultiValue::new_or_cached(lua);
-        values.refill(self.0.into_iter().map(|e| e.to_lua(lua)))?;
+    fn into_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
+        let mut values = MultiValue::new_or_pooled(lua);
+        values.refill(self.0.into_iter().map(|e| e.into_lua(lua)))?;
         Ok(values)
     }
 }
@@ -145,42 +155,42 @@ impl<'lua, T: FromLua<'lua>> FromLuaMulti<'lua> for Variadic<T> {
             .map(|e| T::from_lua(e, lua))
             .collect::<Result<Vec<T>>>()
             .map(Variadic);
-        lua.cache_multivalue(values);
+        MultiValue::return_to_pool(values, lua);
         res
     }
 }
 
 macro_rules! impl_tuple {
     () => (
-        impl<'lua> ToLuaMulti<'lua> for () {
+        impl<'lua> IntoLuaMulti<'lua> for () {
             #[inline]
-            fn to_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
-                Ok(MultiValue::new_or_cached(lua))
+            fn into_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
+                Ok(MultiValue::new_or_pooled(lua))
             }
         }
 
         impl<'lua> FromLuaMulti<'lua> for () {
             #[inline]
             fn from_lua_multi(values: MultiValue<'lua>, lua: &'lua Lua) -> Result<Self> {
-                lua.cache_multivalue(values);
+                MultiValue::return_to_pool(values, lua);
                 Ok(())
             }
         }
     );
 
     ($last:ident $($name:ident)*) => (
-        impl<'lua, $($name,)* $last> ToLuaMulti<'lua> for ($($name,)* $last,)
-            where $($name: ToLua<'lua>,)*
-                  $last: ToLuaMulti<'lua>
+        impl<'lua, $($name,)* $last> IntoLuaMulti<'lua> for ($($name,)* $last,)
+            where $($name: IntoLua<'lua>,)*
+                  $last: IntoLuaMulti<'lua>
         {
             #[allow(unused_mut)]
             #[allow(non_snake_case)]
             #[inline]
-            fn to_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
+            fn into_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>> {
                 let ($($name,)* $last,) = self;
 
-                let mut results = $last.to_lua_multi(lua)?;
-                push_reverse!(results, $($name.to_lua(lua)?,)*);
+                let mut results = $last.into_lua_multi(lua)?;
+                push_reverse!(results, $($name.into_lua(lua)?,)*);
                 Ok(results)
             }
         }
@@ -193,9 +203,21 @@ macro_rules! impl_tuple {
             #[allow(non_snake_case)]
             #[inline]
             fn from_lua_multi(mut values: MultiValue<'lua>, lua: &'lua Lua) -> Result<Self> {
-                $(let $name = values.pop_front().unwrap_or(Nil);)*
+                $(let $name = FromLua::from_lua(values.pop_front().unwrap_or(Nil), lua)?;)*
                 let $last = FromLuaMulti::from_lua_multi(values, lua)?;
-                Ok(($(FromLua::from_lua($name, lua)?,)* $last,))
+                Ok(($($name,)* $last,))
+            }
+
+            #[allow(unused_mut)]
+            #[allow(non_snake_case)]
+            #[inline]
+            fn from_lua_multi_args(mut values: MultiValue<'lua>, mut i: usize, to: Option<&str>, lua: &'lua Lua) -> Result<Self> {
+                $(
+                    let $name = FromLua::from_lua_arg(values.pop_front().unwrap_or(Nil), i, to, lua)?;
+                    i += 1;
+                )*
+                let $last = FromLuaMulti::from_lua_multi_args(values, i, to, lua)?;
+                Ok(($($name,)* $last,))
             }
         }
     );

src/prelude.rs

@@ -2,16 +2,18 @@
 
 #[doc(no_inline)]
 pub use crate::{
-    AnyUserData as LuaAnyUserData, Chunk as LuaChunk, Error as LuaError,
-    ExternalError as LuaExternalError, ExternalResult as LuaExternalResult, FromLua, FromLuaMulti,
-    Function as LuaFunction, FunctionInfo as LuaFunctionInfo, GCMode as LuaGCMode,
-    Integer as LuaInteger, LightUserData as LuaLightUserData, Lua, LuaOptions,
-    MetaMethod as LuaMetaMethod, MultiValue as LuaMultiValue, Nil as LuaNil, Number as LuaNumber,
-    RegistryKey as LuaRegistryKey, Result as LuaResult, StdLib as LuaStdLib, String as LuaString,
-    Table as LuaTable, TableExt as LuaTableExt, TablePairs as LuaTablePairs,
-    TableSequence as LuaTableSequence, Thread as LuaThread, ThreadStatus as LuaThreadStatus, ToLua,
-    ToLuaMulti, UserData as LuaUserData, UserDataFields as LuaUserDataFields,
-    UserDataMetatable as LuaUserDataMetatable, UserDataMethods as LuaUserDataMethods,
+    AnyUserData as LuaAnyUserData, AnyUserDataExt as LuaAnyUserDataExt, Chunk as LuaChunk,
+    Error as LuaError, ErrorContext as LuaErrorContext, ExternalError as LuaExternalError,
+    ExternalResult as LuaExternalResult, FromLua, FromLuaMulti, Function as LuaFunction,
+    FunctionInfo as LuaFunctionInfo, GCMode as LuaGCMode, Integer as LuaInteger, IntoLua,
+    IntoLuaMulti, LightUserData as LuaLightUserData, Lua, LuaOptions, MetaMethod as LuaMetaMethod,
+    MultiValue as LuaMultiValue, Nil as LuaNil, Number as LuaNumber, RegistryKey as LuaRegistryKey,
+    Result as LuaResult, StdLib as LuaStdLib, String as LuaString, Table as LuaTable,
+    TableExt as LuaTableExt, TablePairs as LuaTablePairs, TableSequence as LuaTableSequence,
+    Thread as LuaThread, ThreadStatus as LuaThreadStatus, UserData as LuaUserData,
+    UserDataFields as LuaUserDataFields, UserDataMetatable as LuaUserDataMetatable,
+    UserDataMethods as LuaUserDataMethods, UserDataRef as LuaUserDataRef,
+    UserDataRefMut as LuaUserDataRefMut, UserDataRegistrar as LuaUserDataRegistrar,
     Value as LuaValue,
 };
 
@@ -33,3 +35,10 @@ pub use crate::{
     DeserializeOptions as LuaDeserializeOptions, LuaSerdeExt,
     SerializeOptions as LuaSerializeOptions,
 };
+
+#[cfg(feature = "unstable")]
+#[doc(no_inline)]
+pub use crate::{
+    OwnedAnyUserData as LuaOwnedAnyUserData, OwnedFunction as LuaOwnedFunction,
+    OwnedString as LuaOwnedString, OwnedTable as LuaOwnedTable,
+};

src/serde/de.rs

@@ -9,6 +9,7 @@ use serde::de::{self, IntoDeserializer};
 
 use crate::error::{Error, Result};
 use crate::table::{Table, TablePairs, TableSequence};
+use crate::userdata::AnyUserData;
 use crate::value::Value;
 
 /// A struct for deserializing Lua values into Rust values.
@@ -131,6 +132,9 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
             Value::Table(ref t) if t.raw_len() > 0 || t.is_array() => self.deserialize_seq(visitor),
             Value::Table(_) => self.deserialize_map(visitor),
             Value::LightUserData(ud) if ud.0.is_null() => visitor.visit_none(),
+            Value::UserData(ud) if ud.is_serializable() => {
+                serde_userdata(ud, |value| value.deserialize_any(visitor))
+            }
             Value::Function(_)
             | Value::Thread(_)
             | Value::UserData(_)
@@ -163,8 +167,8 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
     #[inline]
     fn deserialize_enum<V>(
         self,
-        _name: &str,
-        _variants: &'static [&'static str],
+        name: &'static str,
+        variants: &'static [&'static str],
         visitor: V,
     ) -> Result<V::Value>
     where
@@ -198,6 +202,9 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
                 (variant, Some(value), Some(_guard))
             }
             Value::String(variant) => (variant.to_str()?.to_owned(), None, None),
+            Value::UserData(ud) if ud.is_serializable() => {
+                return serde_userdata(ud, |value| value.deserialize_enum(name, variants, visitor));
+            }
             _ => return Err(de::Error::custom("bad enum value")),
         };
 
@@ -244,6 +251,9 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
                     ))
                 }
             }
+            Value::UserData(ud) if ud.is_serializable() => {
+                serde_userdata(ud, |value| value.deserialize_seq(visitor))
+            }
             value => Err(de::Error::invalid_type(
                 de::Unexpected::Other(value.type_name()),
                 &"table",
@@ -299,6 +309,9 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
                     ))
                 }
             }
+            Value::UserData(ud) if ud.is_serializable() => {
+                serde_userdata(ud, |value| value.deserialize_map(visitor))
+            }
             value => Err(de::Error::invalid_type(
                 de::Unexpected::Other(value.type_name()),
                 &"table",
@@ -320,11 +333,16 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
     }
 
     #[inline]
-    fn deserialize_newtype_struct<V>(self, _name: &'static str, visitor: V) -> Result<V::Value>
+    fn deserialize_newtype_struct<V>(self, name: &'static str, visitor: V) -> Result<V::Value>
     where
         V: de::Visitor<'de>,
     {
-        visitor.visit_newtype_struct(self)
+        match self.value {
+            Value::UserData(ud) if ud.is_serializable() => {
+                serde_userdata(ud, |value| value.deserialize_newtype_struct(name, visitor))
+            }
+            _ => visitor.visit_newtype_struct(self),
+        }
     }
 
     #[inline]
@@ -612,6 +630,7 @@ fn check_value_if_skip(
                 return Ok(true); // skip
             }
         }
+        Value::UserData(ud) if ud.is_serializable() => {}
         Value::Function(_)
         | Value::Thread(_)
         | Value::UserData(_)
@@ -625,3 +644,11 @@ fn check_value_if_skip(
     }
     Ok(false) // do not skip
 }
+
+fn serde_userdata<V>(
+    ud: AnyUserData,
+    f: impl FnOnce(serde_value::Value) -> std::result::Result<V, serde_value::DeserializerError>,
+) -> Result<V> {
+    let value = serde_value::to_value(ud).map_err(|err| Error::SerializeError(err.to_string()))?;
+    f(value).map_err(|err| Error::DeserializeError(err.to_string()))
+}

src/serde/mod.rs

@@ -1,21 +1,19 @@
 //! (De)Serialization support using serde.
 
 use std::os::raw::c_void;
-use std::ptr;
 
-use serde::{Deserialize, Serialize};
+use serde::{de::DeserializeOwned, ser::Serialize};
 
 use crate::error::Result;
-use crate::ffi;
 use crate::lua::Lua;
+use crate::private::Sealed;
 use crate::table::Table;
-use crate::types::LightUserData;
 use crate::util::check_stack;
 use crate::value::Value;
 
 /// Trait for serializing/deserializing Lua values using Serde.
 #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
-pub trait LuaSerdeExt<'lua> {
+pub trait LuaSerdeExt: Sealed {
     /// A special value (lightuserdata) to encode/decode optional (none) values.
     ///
     /// Requires `feature = "serialize"`
@@ -37,7 +35,7 @@ pub trait LuaSerdeExt<'lua> {
     ///     Ok(())
     /// }
     /// ```
-    fn null(&'lua self) -> Value<'lua>;
+    fn null(&self) -> Value;
 
     /// A metatable attachable to a Lua table to systematically encode it as Array (instead of Map).
     /// As result, encoded Array will contain only sequence part of the table, with the same length
@@ -68,7 +66,7 @@ pub trait LuaSerdeExt<'lua> {
     ///     Ok(())
     /// }
     /// ```
-    fn array_metatable(&'lua self) -> Table<'lua>;
+    fn array_metatable(&self) -> Table;
 
     /// Converts `T` into a [`Value`] instance.
     ///
@@ -101,7 +99,7 @@ pub trait LuaSerdeExt<'lua> {
     ///     "#).exec()
     /// }
     /// ```
-    fn to_value<T: Serialize + ?Sized>(&'lua self, t: &T) -> Result<Value<'lua>>;
+    fn to_value<'lua, T: Serialize + ?Sized>(&'lua self, t: &T) -> Result<Value<'lua>>;
 
     /// Converts `T` into a [`Value`] instance with options.
     ///
@@ -126,7 +124,7 @@ pub trait LuaSerdeExt<'lua> {
     ///     "#).exec()
     /// }
     /// ```
-    fn to_value_with<T>(&'lua self, t: &T, options: ser::Options) -> Result<Value<'lua>>
+    fn to_value_with<'lua, T>(&'lua self, t: &T, options: ser::Options) -> Result<Value<'lua>>
     where
         T: Serialize + ?Sized;
 
@@ -159,7 +157,7 @@ pub trait LuaSerdeExt<'lua> {
     /// }
     /// ```
     #[allow(clippy::wrong_self_convention)]
-    fn from_value<T: Deserialize<'lua>>(&'lua self, value: Value<'lua>) -> Result<T>;
+    fn from_value<T: DeserializeOwned>(&self, value: Value) -> Result<T>;
 
     /// Deserializes a [`Value`] into any serde deserializable object with options.
     ///
@@ -191,49 +189,46 @@ pub trait LuaSerdeExt<'lua> {
     /// }
     /// ```
     #[allow(clippy::wrong_self_convention)]
-    fn from_value_with<T: Deserialize<'lua>>(
-        &'lua self,
-        value: Value<'lua>,
-        options: de::Options,
-    ) -> Result<T>;
+    fn from_value_with<T: DeserializeOwned>(&self, value: Value, options: de::Options)
+        -> Result<T>;
 }
 
-impl<'lua> LuaSerdeExt<'lua> for Lua {
-    fn null(&'lua self) -> Value<'lua> {
-        Value::LightUserData(LightUserData(ptr::null_mut()))
+impl LuaSerdeExt for Lua {
+    fn null(&self) -> Value {
+        Value::NULL
     }
 
-    fn array_metatable(&'lua self) -> Table<'lua> {
+    fn array_metatable(&self) -> Table {
         unsafe {
             push_array_metatable(self.ref_thread());
             Table(self.pop_ref_thread())
         }
     }
 
-    fn to_value<T>(&'lua self, t: &T) -> Result<Value<'lua>>
+    fn to_value<'lua, T>(&'lua self, t: &T) -> Result<Value<'lua>>
     where
         T: Serialize + ?Sized,
     {
         t.serialize(ser::Serializer::new(self))
     }
 
-    fn to_value_with<T>(&'lua self, t: &T, options: ser::Options) -> Result<Value<'lua>>
+    fn to_value_with<'lua, T>(&'lua self, t: &T, options: ser::Options) -> Result<Value<'lua>>
     where
         T: Serialize + ?Sized,
     {
         t.serialize(ser::Serializer::new_with_options(self, options))
     }
 
-    fn from_value<T>(&'lua self, value: Value<'lua>) -> Result<T>
+    fn from_value<T>(&self, value: Value) -> Result<T>
     where
-        T: Deserialize<'lua>,
+        T: DeserializeOwned,
     {
         T::deserialize(de::Deserializer::new(value))
     }
 
-    fn from_value_with<T>(&'lua self, value: Value<'lua>, options: de::Options) -> Result<T>
+    fn from_value_with<T>(&self, value: Value, options: de::Options) -> Result<T>
     where
-        T: Deserialize<'lua>,
+        T: DeserializeOwned,
     {
         T::deserialize(de::Deserializer::new_with_options(value, options))
     }

src/serde/ser.rs

@@ -4,13 +4,12 @@ use serde::{ser, Serialize};
 
 use super::LuaSerdeExt;
 use crate::error::{Error, Result};
-use crate::ffi;
 use crate::lua::Lua;
 use crate::string::String;
 use crate::table::Table;
 use crate::types::Integer;
 use crate::util::{check_stack, StackGuard};
-use crate::value::{ToLua, Value};
+use crate::value::{IntoLua, Value};
 
 /// A struct for serializing Rust values into Lua values.
 #[derive(Debug)]
@@ -110,7 +109,7 @@ macro_rules! lua_serialize_number {
     ($name:ident, $t:ty) => {
         #[inline]
         fn $name(self, value: $t) -> Result<Value<'lua>> {
-            value.to_lua(self.lua)
+            value.into_lua(self.lua)
         }
     };
 }
@@ -320,20 +319,21 @@ impl<'lua> ser::SerializeSeq for SerializeVec<'lua> {
         T: Serialize + ?Sized,
     {
         let lua = self.table.0.lua;
+        let state = lua.state();
         let value = lua.to_value_with(value, self.options)?;
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 4)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
 
             lua.push_ref(&self.table.0);
             lua.push_value(value)?;
             if lua.unlikely_memory_error() {
-                let len = ffi::lua_rawlen(lua.state, -2) as Integer;
-                ffi::lua_rawseti(lua.state, -2, len + 1);
-                ffi::lua_pop(lua.state, 1);
+                let len = ffi::lua_rawlen(state, -2) as Integer;
+                ffi::lua_rawseti(state, -2, len + 1);
+                ffi::lua_pop(state, 1);
                 Ok(())
             } else {
-                protect_lua!(lua.state, 2, 0, fn(state) {
+                protect_lua!(state, 2, 0, fn(state) {
                     let len = ffi::lua_rawlen(state, -2) as Integer;
                     ffi::lua_rawseti(state, -2, len + 1);
                 })

src/string.rs

@@ -2,7 +2,7 @@ use std::borrow::{Borrow, Cow};
 use std::hash::{Hash, Hasher};
 use std::os::raw::c_void;
 use std::string::String as StdString;
-use std::{slice, str};
+use std::{fmt, slice, str};
 
 #[cfg(feature = "serialize")]
 use {
@@ -11,15 +11,35 @@ use {
 };
 
 use crate::error::{Error, Result};
-use crate::ffi;
 use crate::types::LuaRef;
 
 /// Handle to an internal Lua string.
 ///
 /// Unlike Rust strings, Lua strings may not be valid UTF-8.
-#[derive(Clone, Debug)]
+#[derive(Clone)]
 pub struct String<'lua>(pub(crate) LuaRef<'lua>);
 
+/// Owned handle to an internal Lua string.
+///
+/// The owned handle holds a *strong* reference to the current Lua instance.
+/// Be warned, if you place it into a Lua type (eg. [`UserData`] or a Rust callback), it is *very easy*
+/// to accidentally cause reference cycles that would prevent destroying Lua instance.
+///
+/// [`UserData`]: crate::UserData
+#[cfg(feature = "unstable")]
+#[cfg_attr(docsrs, doc(cfg(feature = "unstable")))]
+#[derive(Clone)]
+pub struct OwnedString(pub(crate) crate::types::LuaOwnedRef);
+
+#[cfg(feature = "unstable")]
+impl OwnedString {
+    /// Get borrowed handle to the underlying Lua string.
+    #[cfg_attr(feature = "send", allow(unused))]
+    pub const fn to_ref(&self) -> String {
+        String(self.0.to_ref())
+    }
+}
+
 impl<'lua> String<'lua> {
     /// Get a `&str` slice if the Lua string is valid UTF-8.
     ///
@@ -122,6 +142,43 @@ impl<'lua> String<'lua> {
         let ref_thread = self.0.lua.ref_thread();
         unsafe { ffi::lua_topointer(ref_thread, self.0.index) }
     }
+
+    /// Convert this handle to owned version.
+    #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+    #[inline]
+    pub fn into_owned(self) -> OwnedString {
+        OwnedString(self.0.into_owned())
+    }
+}
+
+impl<'lua> fmt::Debug for String<'lua> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let bytes = self.as_bytes();
+        // Check if the string is valid utf8
+        if let Ok(s) = str::from_utf8(bytes) {
+            return s.fmt(f);
+        }
+
+        // Format as bytes
+        write!(f, "b\"")?;
+        for &b in bytes {
+            // https://doc.rust-lang.org/reference/tokens.html#byte-escapes
+            match b {
+                b'\n' => write!(f, "\\n")?,
+                b'\r' => write!(f, "\\r")?,
+                b'\t' => write!(f, "\\t")?,
+                b'\\' | b'"' => write!(f, "\\{}", b as char)?,
+                b'\0' => write!(f, "\\0")?,
+                // ASCII printable
+                0x20..=0x7e => write!(f, "{}", b as char)?,
+                _ => write!(f, "\\x{b:02x}")?,
+            }
+        }
+        write!(f, "\"")?;
+
+        Ok(())
+    }
 }
 
 impl<'lua> AsRef<[u8]> for String<'lua> {
@@ -146,7 +203,7 @@ impl<'lua> Borrow<[u8]> for String<'lua> {
 // in other ways.
 impl<'lua, T> PartialEq<T> for String<'lua>
 where
-    T: AsRef<[u8]>,
+    T: AsRef<[u8]> + ?Sized,
 {
     fn eq(&self, other: &T) -> bool {
         self.as_bytes() == other.as_ref()
@@ -173,3 +230,41 @@ impl<'lua> Serialize for String<'lua> {
         }
     }
 }
+
+// Additional shortcuts
+#[cfg(feature = "unstable")]
+impl OwnedString {
+    /// Get a `&str` slice if the Lua string is valid UTF-8.
+    ///
+    /// This is a shortcut for [`String::to_str()`].
+    #[inline]
+    pub fn to_str(&self) -> Result<&str> {
+        let s = self.to_ref();
+        // Reattach lifetime to &self
+        unsafe { std::mem::transmute(s.to_str()) }
+    }
+
+    /// Get the bytes that make up this string.
+    ///
+    /// This is a shortcut for [`String::as_bytes()`].
+    #[inline]
+    pub fn as_bytes(&self) -> &[u8] {
+        let s = self.to_ref();
+        // Reattach lifetime to &self
+        unsafe { std::mem::transmute(s.as_bytes()) }
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl fmt::Debug for OwnedString {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.to_ref().fmt(f)
+    }
+}
+
+#[cfg(test)]
+mod assertions {
+    use super::*;
+
+    static_assertions::assert_not_impl_any!(String: Send);
+}

src/table.rs

@@ -1,3 +1,5 @@
+use std::collections::HashSet;
+use std::fmt;
 use std::marker::PhantomData;
 use std::os::raw::c_void;
 
@@ -9,19 +11,40 @@ use {
 };
 
 use crate::error::{Error, Result};
-use crate::ffi;
 use crate::function::Function;
+use crate::private::Sealed;
 use crate::types::{Integer, LuaRef};
 use crate::util::{assert_stack, check_stack, StackGuard};
-use crate::value::{FromLua, FromLuaMulti, Nil, ToLua, ToLuaMulti, Value};
+use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, Nil, Value};
 
 #[cfg(feature = "async")]
-use {futures_core::future::LocalBoxFuture, futures_util::future};
+use futures_util::future::{self, LocalBoxFuture};
 
 /// Handle to an internal Lua table.
-#[derive(Clone, Debug)]
+#[derive(Clone)]
 pub struct Table<'lua>(pub(crate) LuaRef<'lua>);
 
+/// Owned handle to an internal Lua table.
+///
+/// The owned handle holds a *strong* reference to the current Lua instance.
+/// Be warned, if you place it into a Lua type (eg. [`UserData`] or a Rust callback), it is *very easy*
+/// to accidentally cause reference cycles that would prevent destroying Lua instance.
+///
+/// [`UserData`]: crate::UserData
+#[cfg(feature = "unstable")]
+#[cfg_attr(docsrs, doc(cfg(feature = "unstable")))]
+#[derive(Clone, Debug)]
+pub struct OwnedTable(pub(crate) crate::types::LuaOwnedRef);
+
+#[cfg(feature = "unstable")]
+impl OwnedTable {
+    /// Get borrowed handle to the underlying Lua table.
+    #[cfg_attr(feature = "send", allow(unused))]
+    pub const fn to_ref(&self) -> Table {
+        Table(self.0.to_ref())
+    }
+}
+
 #[allow(clippy::len_without_is_empty)]
 impl<'lua> Table<'lua> {
     /// Sets a key-value pair in the table.
@@ -57,24 +80,25 @@ impl<'lua> Table<'lua> {
     /// ```
     ///
     /// [`raw_set`]: #method.raw_set
-    pub fn set<K: ToLua<'lua>, V: ToLua<'lua>>(&self, key: K, value: V) -> Result<()> {
+    pub fn set<K: IntoLua<'lua>, V: IntoLua<'lua>>(&self, key: K, value: V) -> Result<()> {
         // Fast track
         if !self.has_metatable() {
             return self.raw_set(key, value);
         }
 
         let lua = self.0.lua;
-        let key = key.to_lua(lua)?;
-        let value = value.to_lua(lua)?;
+        let key = key.into_lua(lua)?;
+        let value = value.into_lua(lua)?;
 
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 5)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 5)?;
 
             lua.push_ref(&self.0);
             lua.push_value(key)?;
             lua.push_value(value)?;
-            protect_lua!(lua.state, 3, 0, fn(state) ffi::lua_settable(state, -3))
+            protect_lua!(state, 3, 0, fn(state) ffi::lua_settable(state, -3))
         }
     }
 
@@ -102,22 +126,23 @@ impl<'lua> Table<'lua> {
     /// ```
     ///
     /// [`raw_get`]: #method.raw_get
-    pub fn get<K: ToLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V> {
+    pub fn get<K: IntoLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V> {
         // Fast track
         if !self.has_metatable() {
             return self.raw_get(key);
         }
 
         let lua = self.0.lua;
-        let key = key.to_lua(lua)?;
+        let state = lua.state();
+        let key = key.into_lua(lua)?;
 
         let value = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 4)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
 
             lua.push_ref(&self.0);
             lua.push_value(key)?;
-            protect_lua!(lua.state, 2, 1, fn(state) ffi::lua_gettable(state, -2))?;
+            protect_lua!(state, 2, 1, fn(state) ffi::lua_gettable(state, -2))?;
 
             lua.pop_value()
         };
@@ -125,26 +150,27 @@ impl<'lua> Table<'lua> {
     }
 
     /// Checks whether the table contains a non-nil value for `key`.
-    pub fn contains_key<K: ToLua<'lua>>(&self, key: K) -> Result<bool> {
+    pub fn contains_key<K: IntoLua<'lua>>(&self, key: K) -> Result<bool> {
         Ok(self.get::<_, Value>(key)? != Value::Nil)
     }
 
     /// Appends a value to the back of the table.
-    pub fn push<V: ToLua<'lua>>(&self, value: V) -> Result<()> {
+    pub fn push<V: IntoLua<'lua>>(&self, value: V) -> Result<()> {
         // Fast track
         if !self.has_metatable() {
             return self.raw_push(value);
         }
 
         let lua = self.0.lua;
-        let value = value.to_lua(lua)?;
+        let state = lua.state();
+        let value = value.into_lua(lua)?;
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 4)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
 
             lua.push_ref(&self.0);
             lua.push_value(value)?;
-            protect_lua!(lua.state, 2, 0, fn(state) {
+            protect_lua!(state, 2, 0, fn(state) {
                 let len = ffi::luaL_len(state, -2) as Integer;
                 ffi::lua_seti(state, -2, len + 1);
             })?
@@ -160,12 +186,13 @@ impl<'lua> Table<'lua> {
         }
 
         let lua = self.0.lua;
+        let state = lua.state();
         let value = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 4)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
 
             lua.push_ref(&self.0);
-            protect_lua!(lua.state, 1, 1, fn(state) {
+            protect_lua!(state, 1, 1, fn(state) {
                 let len = ffi::luaL_len(state, -1) as Integer;
                 ffi::lua_geti(state, -1, len);
                 ffi::lua_pushnil(state);
@@ -233,44 +260,46 @@ impl<'lua> Table<'lua> {
     }
 
     /// Sets a key-value pair without invoking metamethods.
-    pub fn raw_set<K: ToLua<'lua>, V: ToLua<'lua>>(&self, key: K, value: V) -> Result<()> {
+    pub fn raw_set<K: IntoLua<'lua>, V: IntoLua<'lua>>(&self, key: K, value: V) -> Result<()> {
         #[cfg(feature = "luau")]
         self.check_readonly_write()?;
 
         let lua = self.0.lua;
-        let key = key.to_lua(lua)?;
-        let value = value.to_lua(lua)?;
+        let state = lua.state();
+        let key = key.into_lua(lua)?;
+        let value = value.into_lua(lua)?;
 
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 5)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 5)?;
 
             lua.push_ref(&self.0);
             lua.push_value(key)?;
             lua.push_value(value)?;
 
             if lua.unlikely_memory_error() {
-                ffi::lua_rawset(lua.state, -3);
-                ffi::lua_pop(lua.state, 1);
+                ffi::lua_rawset(state, -3);
+                ffi::lua_pop(state, 1);
                 Ok(())
             } else {
-                protect_lua!(lua.state, 3, 0, fn(state) ffi::lua_rawset(state, -3))
+                protect_lua!(state, 3, 0, fn(state) ffi::lua_rawset(state, -3))
             }
         }
     }
 
     /// Gets the value associated to `key` without invoking metamethods.
-    pub fn raw_get<K: ToLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V> {
+    pub fn raw_get<K: IntoLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V> {
         let lua = self.0.lua;
-        let key = key.to_lua(lua)?;
+        let state = lua.state();
+        let key = key.into_lua(lua)?;
 
         let value = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 3)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 3)?;
 
             lua.push_ref(&self.0);
             lua.push_value(key)?;
-            ffi::lua_rawget(lua.state, -2);
+            ffi::lua_rawget(state, -2);
 
             lua.pop_value()
         };
@@ -279,21 +308,23 @@ impl<'lua> Table<'lua> {
 
     /// Inserts element value at position `idx` to the table, shifting up the elements from `table[idx]`.
     /// The worst case complexity is O(n), where n is the table length.
-    pub fn raw_insert<V: ToLua<'lua>>(&self, idx: Integer, value: V) -> Result<()> {
+    pub fn raw_insert<V: IntoLua<'lua>>(&self, idx: Integer, value: V) -> Result<()> {
         let lua = self.0.lua;
+        let state = lua.state();
+
         let size = self.raw_len();
         if idx < 1 || idx > size + 1 {
             return Err(Error::RuntimeError("index out of bounds".to_string()));
         }
 
-        let value = value.to_lua(lua)?;
+        let value = value.into_lua(lua)?;
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 5)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 5)?;
 
             lua.push_ref(&self.0);
             lua.push_value(value)?;
-            protect_lua!(lua.state, 2, 0, |state| {
+            protect_lua!(state, 2, 0, |state| {
                 for i in (idx..=size).rev() {
                     // table[i+1] = table[i]
                     ffi::lua_rawgeti(state, -2, i);
@@ -305,16 +336,17 @@ impl<'lua> Table<'lua> {
     }
 
     /// Appends a value to the back of the table without invoking metamethods.
-    pub fn raw_push<V: ToLua<'lua>>(&self, value: V) -> Result<()> {
+    pub fn raw_push<V: IntoLua<'lua>>(&self, value: V) -> Result<()> {
         #[cfg(feature = "luau")]
         self.check_readonly_write()?;
 
         let lua = self.0.lua;
-        let value = value.to_lua(lua)?;
+        let state = lua.state();
+        let value = value.into_lua(lua)?;
 
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 4)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
 
             lua.push_ref(&self.0);
             lua.push_value(value)?;
@@ -325,9 +357,9 @@ impl<'lua> Table<'lua> {
             }
 
             if lua.unlikely_memory_error() {
-                callback(lua.state);
+                callback(state);
             } else {
-                protect_lua!(lua.state, 2, 0, fn(state) callback(state))?;
+                protect_lua!(state, 2, 0, fn(state) callback(state))?;
             }
         }
         Ok(())
@@ -339,16 +371,17 @@ impl<'lua> Table<'lua> {
         self.check_readonly_write()?;
 
         let lua = self.0.lua;
+        let state = lua.state();
         let value = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 3)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 3)?;
 
             lua.push_ref(&self.0);
-            let len = ffi::lua_rawlen(lua.state, -1) as Integer;
-            ffi::lua_rawgeti(lua.state, -1, len);
+            let len = ffi::lua_rawlen(state, -1) as Integer;
+            ffi::lua_rawgeti(state, -1, len);
             // Set slot to nil (it must be safe to do)
-            ffi::lua_pushnil(lua.state);
-            ffi::lua_rawseti(lua.state, -3, len);
+            ffi::lua_pushnil(state);
+            ffi::lua_rawseti(state, -3, len);
             lua.pop_value()
         };
         V::from_lua(value, lua)
@@ -361,9 +394,10 @@ impl<'lua> Table<'lua> {
     /// where n is the table length.
     ///
     /// For other key types this is equivalent to setting `table[key] = nil`.
-    pub fn raw_remove<K: ToLua<'lua>>(&self, key: K) -> Result<()> {
+    pub fn raw_remove<K: IntoLua<'lua>>(&self, key: K) -> Result<()> {
         let lua = self.0.lua;
-        let key = key.to_lua(lua)?;
+        let state = lua.state();
+        let key = key.into_lua(lua)?;
         match key {
             Value::Integer(idx) => {
                 let size = self.raw_len();
@@ -371,11 +405,11 @@ impl<'lua> Table<'lua> {
                     return Err(Error::RuntimeError("index out of bounds".to_string()));
                 }
                 unsafe {
-                    let _sg = StackGuard::new(lua.state);
-                    check_stack(lua.state, 4)?;
+                    let _sg = StackGuard::new(state);
+                    check_stack(state, 4)?;
 
                     lua.push_ref(&self.0);
-                    protect_lua!(lua.state, 1, 0, |state| {
+                    protect_lua!(state, 1, 0, |state| {
                         for i in idx..size {
                             ffi::lua_rawgeti(state, -1, i + 1);
                             ffi::lua_rawseti(state, -2, i);
@@ -389,6 +423,47 @@ impl<'lua> Table<'lua> {
         }
     }
 
+    /// Clears the table, removing all keys and values from array and hash parts,
+    /// without invoking metamethods.
+    ///
+    /// This method is useful to clear the table while keeping its capacity.
+    pub fn clear(&self) -> Result<()> {
+        #[cfg(feature = "luau")]
+        self.check_readonly_write()?;
+
+        let lua = self.0.lua;
+        unsafe {
+            #[cfg(feature = "luau")]
+            ffi::lua_cleartable(lua.ref_thread(), self.0.index);
+
+            #[cfg(not(feature = "luau"))]
+            {
+                let state = lua.state();
+                check_stack(state, 4)?;
+
+                lua.push_ref(&self.0);
+
+                // Clear array part
+                for i in 1..=ffi::lua_rawlen(state, -1) {
+                    ffi::lua_pushnil(state);
+                    ffi::lua_rawseti(state, -2, i as Integer);
+                }
+
+                // Clear hash part
+                // It must be safe as long as we don't use invalid keys
+                ffi::lua_pushnil(state);
+                while ffi::lua_next(state, -2) != 0 {
+                    ffi::lua_pop(state, 1); // pop value
+                    ffi::lua_pushvalue(state, -1); // copy key
+                    ffi::lua_pushnil(state);
+                    ffi::lua_rawset(state, -4);
+                }
+            }
+        }
+
+        Ok(())
+    }
+
     /// Returns the result of the Lua `#` operator.
     ///
     /// This might invoke the `__len` metamethod. Use the [`raw_len`] method if that is not desired.
@@ -401,12 +476,13 @@ impl<'lua> Table<'lua> {
         }
 
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 4)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 4)?;
 
             lua.push_ref(&self.0);
-            protect_lua!(lua.state, 1, 0, |state| ffi::luaL_len(state, -1))
+            protect_lua!(state, 1, 0, |state| ffi::luaL_len(state, -1))
         }
     }
 
@@ -421,12 +497,13 @@ impl<'lua> Table<'lua> {
     /// Unlike the `getmetatable` Lua function, this method ignores the `__metatable` field.
     pub fn get_metatable(&self) -> Option<Table<'lua>> {
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 2);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 2);
 
             lua.push_ref(&self.0);
-            if ffi::lua_getmetatable(lua.state, -1) == 0 {
+            if ffi::lua_getmetatable(state, -1) == 0 {
                 None
             } else {
                 Some(Table(lua.pop_ref()))
@@ -446,17 +523,18 @@ impl<'lua> Table<'lua> {
         }
 
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 2);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 2);
 
             lua.push_ref(&self.0);
             if let Some(metatable) = metatable {
                 lua.push_ref(&metatable.0);
             } else {
-                ffi::lua_pushnil(lua.state);
+                ffi::lua_pushnil(state);
             }
-            ffi::lua_setmetatable(lua.state, -2);
+            ffi::lua_setmetatable(state, -2);
         }
     }
 
@@ -512,6 +590,14 @@ impl<'lua> Table<'lua> {
         unsafe { ffi::lua_topointer(ref_thread, self.0.index) }
     }
 
+    /// Convert this handle to owned version.
+    #[cfg(all(feature = "unstable", any(not(feature = "send"), doc)))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "unstable", not(feature = "send")))))]
+    #[inline]
+    pub fn into_owned(self) -> OwnedTable {
+        OwnedTable(self.0.into_owned())
+    }
+
     /// Consume this table and return an iterator over the pairs of the table.
     ///
     /// This works like the Lua `pairs` function, but does not invoke the `__pairs` metamethod.
@@ -619,7 +705,7 @@ impl<'lua> Table<'lua> {
         }
     }
 
-    #[cfg(any(feature = "serialize"))]
+    #[cfg(feature = "serialize")]
     pub(crate) fn raw_sequence_values_by_len<V: FromLua<'lua>>(
         self,
         len: Option<Integer>,
@@ -637,16 +723,17 @@ impl<'lua> Table<'lua> {
     #[cfg(feature = "serialize")]
     pub(crate) fn is_array(&self) -> bool {
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 3);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 3);
 
             lua.push_ref(&self.0);
-            if ffi::lua_getmetatable(lua.state, -1) == 0 {
+            if ffi::lua_getmetatable(state, -1) == 0 {
                 return false;
             }
-            crate::serde::push_array_metatable(lua.state);
-            ffi::lua_rawequal(lua.state, -1, -2) != 0
+            crate::serde::push_array_metatable(state);
+            ffi::lua_rawequal(state, -1, -2) != 0
         }
     }
 
@@ -659,6 +746,42 @@ impl<'lua> Table<'lua> {
         }
         Ok(())
     }
+
+    pub(crate) fn fmt_pretty(
+        &self,
+        fmt: &mut fmt::Formatter,
+        ident: usize,
+        visited: &mut HashSet<*const c_void>,
+    ) -> fmt::Result {
+        visited.insert(self.to_pointer());
+
+        let t = self.clone();
+        // Collect key/value pairs into a vector so we can sort them
+        let mut pairs = t.pairs::<Value, Value>().flatten().collect::<Vec<_>>();
+        // Sort keys
+        pairs.sort_by(|(a, _), (b, _)| a.cmp(b));
+        if pairs.is_empty() {
+            return write!(fmt, "{{}}");
+        }
+        writeln!(fmt, "{{")?;
+        for (key, value) in pairs {
+            write!(fmt, "{}[", " ".repeat(ident + 2))?;
+            key.fmt_pretty(fmt, false, ident + 2, visited)?;
+            write!(fmt, "] = ")?;
+            value.fmt_pretty(fmt, true, ident + 2, visited)?;
+            writeln!(fmt, ",")?;
+        }
+        write!(fmt, "{}}}", " ".repeat(ident))
+    }
+}
+
+impl fmt::Debug for Table<'_> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        if fmt.alternate() {
+            return self.fmt_pretty(fmt, 0, &mut HashSet::new());
+        }
+        fmt.write_fmt(format_args!("Table({:?})", self.0))
+    }
 }
 
 impl<'lua> PartialEq for Table<'lua> {
@@ -675,13 +798,13 @@ impl<'lua> AsRef<Table<'lua>> for Table<'lua> {
 }
 
 /// An extension trait for `Table`s that provides a variety of convenient functionality.
-pub trait TableExt<'lua> {
+pub trait TableExt<'lua>: Sealed {
     /// Calls the table as function assuming it has `__call` metamethod.
     ///
     /// The metamethod is called with the table as its first argument, followed by the passed arguments.
     fn call<A, R>(&self, args: A) -> Result<R>
     where
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>;
 
     /// Asynchronously calls the table as function assuming it has `__call` metamethod.
@@ -692,7 +815,7 @@ pub trait TableExt<'lua> {
     fn call_async<'fut, A, R>(&self, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut;
 
     /// Gets the function associated to `key` from the table and executes it,
@@ -704,8 +827,8 @@ pub trait TableExt<'lua> {
     /// This might invoke the `__index` metamethod.
     fn call_method<K, A, R>(&self, key: K, args: A) -> Result<R>
     where
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>;
 
     /// Gets the function associated to `key` from the table and executes it,
@@ -717,8 +840,8 @@ pub trait TableExt<'lua> {
     /// This might invoke the `__index` metamethod.
     fn call_function<K, A, R>(&self, key: K, args: A) -> Result<R>
     where
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>;
 
     /// Gets the function associated to `key` from the table and asynchronously executes it,
@@ -732,8 +855,8 @@ pub trait TableExt<'lua> {
     fn call_async_method<'fut, K, A, R>(&self, key: K, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut;
 
     /// Gets the function associated to `key` from the table and asynchronously executes it,
@@ -751,15 +874,15 @@ pub trait TableExt<'lua> {
     ) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut;
 }
 
 impl<'lua> TableExt<'lua> for Table<'lua> {
     fn call<A, R>(&self, args: A) -> Result<R>
     where
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>,
     {
         // Convert table to a function and call via pcall that respects the `__call` metamethod.
@@ -770,7 +893,7 @@ impl<'lua> TableExt<'lua> for Table<'lua> {
     fn call_async<'fut, A, R>(&self, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut,
     {
         Function(self.0.clone()).call_async(args)
@@ -778,20 +901,20 @@ impl<'lua> TableExt<'lua> for Table<'lua> {
 
     fn call_method<K, A, R>(&self, key: K, args: A) -> Result<R>
     where
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>,
     {
         let lua = self.0.lua;
-        let mut args = args.to_lua_multi(lua)?;
+        let mut args = args.into_lua_multi(lua)?;
         args.push_front(Value::Table(self.clone()));
         self.get::<_, Function>(key)?.call(args)
     }
 
     fn call_function<K, A, R>(&self, key: K, args: A) -> Result<R>
     where
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>,
     {
         self.get::<_, Function>(key)?.call(args)
@@ -801,12 +924,12 @@ impl<'lua> TableExt<'lua> for Table<'lua> {
     fn call_async_method<'fut, K, A, R>(&self, key: K, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut,
     {
         let lua = self.0.lua;
-        let mut args = match args.to_lua_multi(lua) {
+        let mut args = match args.into_lua_multi(lua) {
             Ok(args) => args,
             Err(e) => return Box::pin(future::err(e)),
         };
@@ -818,8 +941,8 @@ impl<'lua> TableExt<'lua> for Table<'lua> {
     fn call_async_function<'fut, K, A, R>(&self, key: K, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
-        K: ToLua<'lua>,
-        A: ToLuaMulti<'lua>,
+        K: IntoLua<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua> + 'fut,
     {
         match self.get::<_, Function>(key) {
@@ -894,15 +1017,16 @@ where
     fn next(&mut self) -> Option<Self::Item> {
         if let Some(prev_key) = self.key.take() {
             let lua = self.table.lua;
+            let state = lua.state();
 
             let res = (|| unsafe {
-                let _sg = StackGuard::new(lua.state);
-                check_stack(lua.state, 5)?;
+                let _sg = StackGuard::new(state);
+                check_stack(state, 5)?;
 
                 lua.push_ref(&self.table);
                 lua.push_value(prev_key)?;
 
-                let next = protect_lua!(lua.state, 2, ffi::LUA_MULTRET, |state| {
+                let next = protect_lua!(state, 2, ffi::LUA_MULTRET, |state| {
                     ffi::lua_next(state, -2)
                 })?;
                 if next != 0 {
@@ -954,16 +1078,17 @@ where
     fn next(&mut self) -> Option<Self::Item> {
         if let Some(index) = self.index.take() {
             let lua = self.table.lua;
+            let state = lua.state();
 
             let res = (|| unsafe {
-                let _sg = StackGuard::new(lua.state);
-                check_stack(lua.state, 1 + if self.raw { 0 } else { 3 })?;
+                let _sg = StackGuard::new(state);
+                check_stack(state, 1 + if self.raw { 0 } else { 3 })?;
 
                 lua.push_ref(&self.table);
                 let res = if self.raw {
-                    ffi::lua_rawgeti(lua.state, -1, index)
+                    ffi::lua_rawgeti(state, -1, index)
                 } else {
-                    protect_lua!(lua.state, 1, 1, |state| ffi::lua_geti(state, -1, index))?
+                    protect_lua!(state, 1, 1, |state| ffi::lua_geti(state, -1, index))?
                 };
                 match res {
                     ffi::LUA_TNIL if index > self.len.unwrap_or(0) => Ok(None),
@@ -984,3 +1109,13 @@ where
         }
     }
 }
+
+#[cfg(test)]
+mod assertions {
+    use super::*;
+
+    static_assertions::assert_not_impl_any!(Table: Send);
+
+    #[cfg(feature = "unstable")]
+    static_assertions::assert_not_impl_any!(OwnedTable: Send);
+}

src/thread.rs

@@ -2,10 +2,11 @@ use std::cmp;
 use std::os::raw::c_int;
 
 use crate::error::{Error, Result};
-use crate::ffi;
+#[allow(unused)]
+use crate::lua::Lua;
 use crate::types::LuaRef;
 use crate::util::{check_stack, error_traceback_thread, pop_error, StackGuard};
-use crate::value::{FromLuaMulti, ToLuaMulti};
+use crate::value::{FromLuaMulti, IntoLuaMulti};
 
 #[cfg(any(
     feature = "lua54",
@@ -14,17 +15,24 @@ use crate::value::{FromLuaMulti, ToLuaMulti};
 ))]
 use crate::function::Function;
 
+#[cfg(not(feature = "luau"))]
+use crate::{
+    hook::{Debug, HookTriggers},
+    types::MaybeSend,
+};
+
 #[cfg(feature = "async")]
 use {
     crate::{
-        lua::{Lua, ASYNC_POLL_PENDING},
+        lua::ASYNC_POLL_PENDING,
         value::{MultiValue, Value},
     },
-    futures_core::{future::Future, stream::Stream},
+    futures_util::stream::Stream,
     std::{
-        cell::RefCell,
+        future::Future,
         marker::PhantomData,
         pin::Pin,
+        ptr::NonNull,
         task::{Context, Poll, Waker},
     },
 };
@@ -56,10 +64,10 @@ pub struct Thread<'lua>(pub(crate) LuaRef<'lua>);
 /// [`Stream`]: futures_core::stream::Stream
 #[cfg(feature = "async")]
 #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
-#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
 pub struct AsyncThread<'lua, R> {
     thread: Thread<'lua>,
-    args0: RefCell<Option<Result<MultiValue<'lua>>>>,
+    args0: Option<Result<MultiValue<'lua>>>,
     ret: PhantomData<R>,
     recycle: bool,
 }
@@ -108,15 +116,17 @@ impl<'lua> Thread<'lua> {
     /// ```
     pub fn resume<A, R>(&self, args: A) -> Result<R>
     where
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>,
     {
         let lua = self.0.lua;
-        let mut args = args.to_lua_multi(lua)?;
+        let state = lua.state();
+
+        let mut args = args.into_lua_multi(lua)?;
         let nargs = args.len() as c_int;
         let results = unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, cmp::max(nargs + 1, 3))?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, cmp::max(nargs + 1, 3))?;
 
             let thread_state = ffi::lua_tothread(lua.ref_thread(), self.0.index);
 
@@ -129,23 +139,27 @@ impl<'lua> Thread<'lua> {
             for arg in args.drain_all() {
                 lua.push_value(arg)?;
             }
-            ffi::lua_xmove(lua.state, thread_state, nargs);
+            ffi::lua_xmove(state, thread_state, nargs);
 
             let mut nresults = 0;
 
-            let ret = ffi::lua_resume(thread_state, lua.state, nargs, &mut nresults as *mut c_int);
+            let ret = ffi::lua_resume(thread_state, state, nargs, &mut nresults as *mut c_int);
             if ret != ffi::LUA_OK && ret != ffi::LUA_YIELD {
-                check_stack(lua.state, 3)?;
-                protect_lua!(lua.state, 0, 1, |state| error_traceback_thread(
+                if ret == ffi::LUA_ERRMEM {
+                    // Don't call error handler for memory errors
+                    return Err(pop_error(thread_state, ret));
+                }
+                check_stack(state, 3)?;
+                protect_lua!(state, 0, 1, |state| error_traceback_thread(
                     state,
                     thread_state
                 ))?;
-                return Err(pop_error(lua.state, ret));
+                return Err(pop_error(state, ret));
             }
 
             let mut results = args; // Reuse MultiValue container
-            check_stack(lua.state, nresults + 2)?; // 2 is extra for `lua.pop_value()` below
-            ffi::lua_xmove(thread_state, lua.state, nresults);
+            check_stack(state, nresults + 2)?; // 2 is extra for `lua.pop_value()` below
+            ffi::lua_xmove(thread_state, state, nresults);
 
             for _ in 0..nresults {
                 results.push_front(lua.pop_value());
@@ -172,6 +186,23 @@ impl<'lua> Thread<'lua> {
         }
     }
 
+    /// Sets a 'hook' function that will periodically be called as Lua code executes.
+    ///
+    /// This function is similar or [`Lua::set_hook()`] except that it sets for the thread.
+    /// To remove a hook call [`Lua::remove_hook()`].
+    #[cfg(not(feature = "luau"))]
+    #[cfg_attr(docsrs, doc(cfg(not(feature = "luau"))))]
+    pub fn set_hook<F>(&self, triggers: HookTriggers, callback: F)
+    where
+        F: Fn(&Lua, Debug) -> Result<()> + MaybeSend + 'static,
+    {
+        let lua = self.0.lua;
+        unsafe {
+            let thread_state = ffi::lua_tothread(lua.ref_thread(), self.0.index);
+            lua.set_thread_hook(thread_state, triggers, callback);
+        }
+    }
+
     /// Resets a thread
     ///
     /// In [Lua 5.4]: cleans its call stack and closes all pending to-be-closed variables.
@@ -194,33 +225,34 @@ impl<'lua> Thread<'lua> {
     ))]
     pub fn reset(&self, func: Function<'lua>) -> Result<()> {
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            check_stack(lua.state, 2)?;
+            let _sg = StackGuard::new(state);
+            check_stack(state, 2)?;
 
             lua.push_ref(&self.0);
-            let thread_state = ffi::lua_tothread(lua.state, -1);
+            let thread_state = ffi::lua_tothread(state, -1);
 
             #[cfg(all(feature = "lua54", not(feature = "vendored")))]
             let status = ffi::lua_resetthread(thread_state);
             #[cfg(all(feature = "lua54", feature = "vendored"))]
-            let status = ffi::lua_closethread(thread_state, lua.state);
+            let status = ffi::lua_closethread(thread_state, state);
             #[cfg(feature = "lua54")]
             if status != ffi::LUA_OK {
                 return Err(pop_error(thread_state, status));
             }
             #[cfg(all(feature = "luajit", feature = "vendored"))]
-            ffi::lua_resetthread(lua.state, thread_state);
+            ffi::lua_resetthread(state, thread_state);
             #[cfg(feature = "luau")]
             ffi::lua_resetthread(thread_state);
 
             lua.push_ref(&func.0);
-            ffi::lua_xmove(lua.state, thread_state, 1);
+            ffi::lua_xmove(state, thread_state, 1);
 
             #[cfg(feature = "luau")]
             {
-                // Inherit `LUA_GLOBALSINDEX` from the caller
-                ffi::lua_xpush(lua.state, thread_state, ffi::LUA_GLOBALSINDEX);
+                // Inherit `LUA_GLOBALSINDEX` from the main thread
+                ffi::lua_xpush(lua.main_state(), thread_state, ffi::LUA_GLOBALSINDEX);
                 ffi::lua_replace(thread_state, ffi::LUA_GLOBALSINDEX);
             }
 
@@ -277,13 +309,13 @@ impl<'lua> Thread<'lua> {
     #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn into_async<A, R>(self, args: A) -> AsyncThread<'lua, R>
     where
-        A: ToLuaMulti<'lua>,
+        A: IntoLuaMulti<'lua>,
         R: FromLuaMulti<'lua>,
     {
-        let args = args.to_lua_multi(self.0.lua);
+        let args = args.into_lua_multi(self.0.lua);
         AsyncThread {
             thread: self,
-            args0: RefCell::new(Some(args)),
+            args0: Some(args),
             ret: PhantomData,
             recycle: false,
         }
@@ -325,14 +357,12 @@ impl<'lua> Thread<'lua> {
     #[doc(hidden)]
     pub fn sandbox(&self) -> Result<()> {
         let lua = self.0.lua;
+        let state = lua.state();
         unsafe {
             let thread = ffi::lua_tothread(lua.ref_thread(), self.0.index);
-            check_stack(thread, 1)?;
-            check_stack(lua.state, 3)?;
-            // Inherit `LUA_GLOBALSINDEX` from the caller
-            ffi::lua_xpush(lua.state, thread, ffi::LUA_GLOBALSINDEX);
-            ffi::lua_replace(thread, ffi::LUA_GLOBALSINDEX);
-            protect_lua!(lua.state, 0, 0, |_| ffi::luaL_sandboxthread(thread))
+            check_stack(thread, 3)?;
+            check_stack(state, 3)?;
+            protect_lua!(state, 0, 0, |_| ffi::luaL_sandboxthread(thread))
         }
     }
 }
@@ -367,7 +397,10 @@ impl<'lua, R> Drop for AsyncThread<'lua, R> {
                     #[cfg(feature = "lua54")]
                     if self.thread.status() == ThreadStatus::Error {
                         let thread_state = ffi::lua_tothread(lua.ref_thread(), self.thread.0.index);
+                        #[cfg(not(feature = "vendored"))]
                         ffi::lua_resetthread(thread_state);
+                        #[cfg(feature = "vendored")]
+                        ffi::lua_closethread(thread_state, lua.state());
                     }
                 }
             }
@@ -390,11 +423,14 @@ where
             _ => return Poll::Ready(None),
         };
 
-        let _wg = WakerGuard::new(lua, cx.waker().clone());
-        let ret: MultiValue = if let Some(args) = self.args0.borrow_mut().take() {
-            self.thread.resume(args?)?
+        let _wg = WakerGuard::new(lua, cx.waker());
+
+        // This is safe as we are not moving the whole struct
+        let this = unsafe { self.get_unchecked_mut() };
+        let ret: MultiValue = if let Some(args) = this.args0.take() {
+            this.thread.resume(args?)?
         } else {
-            self.thread.resume(())?
+            this.thread.resume(())?
         };
 
         if is_poll_pending(&ret) {
@@ -421,18 +457,21 @@ where
             _ => return Poll::Ready(Err(Error::CoroutineInactive)),
         };
 
-        let _wg = WakerGuard::new(lua, cx.waker().clone());
-        let ret: MultiValue = if let Some(args) = self.args0.borrow_mut().take() {
-            self.thread.resume(args?)?
+        let _wg = WakerGuard::new(lua, cx.waker());
+
+        // This is safe as we are not moving the whole struct
+        let this = unsafe { self.get_unchecked_mut() };
+        let ret: MultiValue = if let Some(args) = this.args0.take() {
+            this.thread.resume(args?)?
         } else {
-            self.thread.resume(())?
+            this.thread.resume(())?
         };
 
         if is_poll_pending(&ret) {
             return Poll::Pending;
         }
 
-        if let ThreadStatus::Resumable = self.thread.status() {
+        if let ThreadStatus::Resumable = this.thread.status() {
             // Ignore value returned via yield()
             cx.waker().wake_by_ref();
             return Poll::Pending;
@@ -454,27 +493,39 @@ fn is_poll_pending(val: &MultiValue) -> bool {
 }
 
 #[cfg(feature = "async")]
-struct WakerGuard<'lua> {
+struct WakerGuard<'lua, 'a> {
     lua: &'lua Lua,
-    prev: Option<Waker>,
+    prev: NonNull<Waker>,
+    _phantom: PhantomData<&'a ()>,
 }
 
 #[cfg(feature = "async")]
-impl<'lua> WakerGuard<'lua> {
+impl<'lua, 'a> WakerGuard<'lua, 'a> {
     #[inline]
-    pub fn new(lua: &Lua, waker: Waker) -> Result<WakerGuard> {
+    pub fn new(lua: &'lua Lua, waker: &'a Waker) -> Result<WakerGuard<'lua, 'a>> {
         unsafe {
-            let prev = lua.set_waker(Some(waker));
-            Ok(WakerGuard { lua, prev })
+            let prev = lua.set_waker(NonNull::from(waker));
+            Ok(WakerGuard {
+                lua,
+                prev,
+                _phantom: PhantomData,
+            })
         }
     }
 }
 
 #[cfg(feature = "async")]
-impl<'lua> Drop for WakerGuard<'lua> {
+impl<'lua, 'a> Drop for WakerGuard<'lua, 'a> {
     fn drop(&mut self) {
         unsafe {
-            self.lua.set_waker(self.prev.take());
+            self.lua.set_waker(self.prev);
         }
     }
 }
+
+#[cfg(test)]
+mod assertions {
+    use super::*;
+
+    static_assertions::assert_not_impl_any!(Thread: Send);
+}

src/types.rs

@@ -1,6 +1,9 @@
-use std::cell::UnsafeCell;
+use std::any::{Any, TypeId};
+use std::cell::{Cell, Ref, RefCell, RefMut, UnsafeCell};
 use std::hash::{Hash, Hasher};
+use std::ops::{Deref, DerefMut};
 use std::os::raw::{c_int, c_void};
+use std::result::Result as StdResult;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
 use std::{fmt, mem, ptr};
@@ -8,17 +11,21 @@ use std::{fmt, mem, ptr};
 #[cfg(feature = "lua54")]
 use std::ffi::CStr;
 
+use rustc_hash::FxHashMap;
+
 #[cfg(feature = "async")]
-use futures_core::future::LocalBoxFuture;
+use futures_util::future::LocalBoxFuture;
 
 use crate::error::Result;
-use crate::ffi;
 #[cfg(not(feature = "luau"))]
 use crate::hook::Debug;
 use crate::lua::{ExtraData, Lua};
 use crate::util::{assert_stack, StackGuard};
 use crate::value::MultiValue;
 
+#[cfg(feature = "unstable")]
+use {crate::lua::LuaInner, std::marker::PhantomData};
+
 /// Type of Lua integer numbers.
 pub type Integer = ffi::lua_Integer;
 /// Type of Lua floating point numbers.
@@ -63,10 +70,10 @@ pub(crate) type HookCallback = Arc<dyn Fn(&Lua, Debug) -> Result<()> + Send>;
 pub(crate) type HookCallback = Arc<dyn Fn(&Lua, Debug) -> Result<()>>;
 
 #[cfg(all(feature = "luau", feature = "send"))]
-pub(crate) type InterruptCallback = Arc<dyn Fn() -> Result<VmState> + Send>;
+pub(crate) type InterruptCallback = Arc<dyn Fn(&Lua) -> Result<VmState> + Send>;
 
 #[cfg(all(feature = "luau", not(feature = "send")))]
-pub(crate) type InterruptCallback = Arc<dyn Fn() -> Result<VmState>>;
+pub(crate) type InterruptCallback = Arc<dyn Fn(&Lua) -> Result<VmState>>;
 
 #[cfg(all(feature = "send", feature = "lua54"))]
 pub(crate) type WarnCallback = Box<dyn Fn(&Lua, &CStr, bool) -> Result<()> + Send>;
@@ -180,6 +187,26 @@ impl RegistryKey {
 pub(crate) struct LuaRef<'lua> {
     pub(crate) lua: &'lua Lua,
     pub(crate) index: c_int,
+    pub(crate) drop: bool,
+}
+
+impl<'lua> LuaRef<'lua> {
+    pub(crate) const fn new(lua: &'lua Lua, index: c_int) -> Self {
+        LuaRef {
+            lua,
+            index,
+            drop: true,
+        }
+    }
+
+    #[cfg(feature = "unstable")]
+    #[inline]
+    pub(crate) fn into_owned(self) -> LuaOwnedRef {
+        assert!(self.drop, "Cannot turn non-drop reference into owned");
+        let owned_ref = LuaOwnedRef::new(self.lua.clone(), self.index);
+        mem::forget(self);
+        owned_ref
+    }
 }
 
 impl<'lua> fmt::Debug for LuaRef<'lua> {
@@ -196,8 +223,8 @@ impl<'lua> Clone for LuaRef<'lua> {
 
 impl<'lua> Drop for LuaRef<'lua> {
     fn drop(&mut self) {
-        if self.index > 0 {
-            self.lua.drop_ref(self);
+        if self.drop {
+            self.lua.drop_ref_index(self.index);
         }
     }
 }
@@ -205,12 +232,216 @@ impl<'lua> Drop for LuaRef<'lua> {
 impl<'lua> PartialEq for LuaRef<'lua> {
     fn eq(&self, other: &Self) -> bool {
         let lua = self.lua;
+        let state = lua.state();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 2);
+            let _sg = StackGuard::new(state);
+            assert_stack(state, 2);
             lua.push_ref(self);
             lua.push_ref(other);
-            ffi::lua_rawequal(lua.state, -1, -2) == 1
+            ffi::lua_rawequal(state, -1, -2) == 1
         }
     }
 }
+
+#[cfg(feature = "unstable")]
+pub(crate) struct LuaOwnedRef {
+    pub(crate) inner: Arc<LuaInner>,
+    pub(crate) index: c_int,
+    _non_send: PhantomData<*const ()>,
+}
+
+#[cfg(feature = "unstable")]
+impl fmt::Debug for LuaOwnedRef {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "OwnedRef({})", self.index)
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl Clone for LuaOwnedRef {
+    fn clone(&self) -> Self {
+        self.to_ref().clone().into_owned()
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl Drop for LuaOwnedRef {
+    fn drop(&mut self) {
+        let lua: &Lua = unsafe { mem::transmute(&self.inner) };
+        lua.drop_ref_index(self.index);
+    }
+}
+
+#[cfg(feature = "unstable")]
+impl LuaOwnedRef {
+    pub(crate) const fn new(inner: Arc<LuaInner>, index: c_int) -> Self {
+        LuaOwnedRef {
+            inner,
+            index,
+            _non_send: PhantomData,
+        }
+    }
+
+    pub(crate) const fn to_ref(&self) -> LuaRef {
+        LuaRef {
+            lua: unsafe { mem::transmute(&self.inner) },
+            index: self.index,
+            drop: false,
+        }
+    }
+}
+
+#[derive(Debug, Default)]
+pub(crate) struct AppData {
+    #[cfg(not(feature = "send"))]
+    container: UnsafeCell<FxHashMap<TypeId, RefCell<Box<dyn Any>>>>,
+    #[cfg(feature = "send")]
+    container: UnsafeCell<FxHashMap<TypeId, RefCell<Box<dyn Any + Send>>>>,
+    borrow: Cell<usize>,
+}
+
+impl AppData {
+    #[track_caller]
+    pub(crate) fn insert<T: MaybeSend + 'static>(&self, data: T) -> Option<T> {
+        match self.try_insert(data) {
+            Ok(data) => data,
+            Err(_) => panic!("cannot mutably borrow app data container"),
+        }
+    }
+
+    pub(crate) fn try_insert<T: MaybeSend + 'static>(&self, data: T) -> StdResult<Option<T>, T> {
+        if self.borrow.get() != 0 {
+            return Err(data);
+        }
+        // SAFETY: we checked that there are no other references to the container
+        Ok(unsafe { &mut *self.container.get() }
+            .insert(TypeId::of::<T>(), RefCell::new(Box::new(data)))
+            .and_then(|data| data.into_inner().downcast::<T>().ok().map(|data| *data)))
+    }
+
+    #[track_caller]
+    pub(crate) fn borrow<T: 'static>(&self) -> Option<AppDataRef<T>> {
+        let data = unsafe { &*self.container.get() }
+            .get(&TypeId::of::<T>())?
+            .borrow();
+        self.borrow.set(self.borrow.get() + 1);
+        Some(AppDataRef {
+            data: Ref::filter_map(data, |data| data.downcast_ref()).ok()?,
+            borrow: &self.borrow,
+        })
+    }
+
+    #[track_caller]
+    pub(crate) fn borrow_mut<T: 'static>(&self) -> Option<AppDataRefMut<T>> {
+        let data = unsafe { &*self.container.get() }
+            .get(&TypeId::of::<T>())?
+            .borrow_mut();
+        self.borrow.set(self.borrow.get() + 1);
+        Some(AppDataRefMut {
+            data: RefMut::filter_map(data, |data| data.downcast_mut()).ok()?,
+            borrow: &self.borrow,
+        })
+    }
+
+    #[track_caller]
+    pub(crate) fn remove<T: 'static>(&self) -> Option<T> {
+        if self.borrow.get() != 0 {
+            panic!("cannot mutably borrow app data container");
+        }
+        // SAFETY: we checked that there are no other references to the container
+        unsafe { &mut *self.container.get() }
+            .remove(&TypeId::of::<T>())?
+            .into_inner()
+            .downcast::<T>()
+            .ok()
+            .map(|data| *data)
+    }
+}
+
+/// A wrapper type for an immutably borrowed value from an app data container.
+///
+/// This type is similar to [`Ref`].
+pub struct AppDataRef<'a, T: ?Sized + 'a> {
+    data: Ref<'a, T>,
+    borrow: &'a Cell<usize>,
+}
+
+impl<T: ?Sized> Drop for AppDataRef<'_, T> {
+    fn drop(&mut self) {
+        self.borrow.set(self.borrow.get() - 1);
+    }
+}
+
+impl<T: ?Sized> Deref for AppDataRef<'_, T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.data
+    }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for AppDataRef<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for AppDataRef<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+/// A wrapper type for a mutably borrowed value from an app data container.
+///
+/// This type is similar to [`RefMut`].
+pub struct AppDataRefMut<'a, T: ?Sized + 'a> {
+    data: RefMut<'a, T>,
+    borrow: &'a Cell<usize>,
+}
+
+impl<T: ?Sized> Drop for AppDataRefMut<'_, T> {
+    fn drop(&mut self) {
+        self.borrow.set(self.borrow.get() - 1);
+    }
+}
+
+impl<T: ?Sized> Deref for AppDataRefMut<'_, T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.data
+    }
+}
+
+impl<T: ?Sized> DerefMut for AppDataRefMut<'_, T> {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.data
+    }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for AppDataRefMut<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for AppDataRefMut<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(f)
+    }
+}
+
+#[cfg(test)]
+mod assertions {
+    use super::*;
+
+    static_assertions::assert_impl_all!(RegistryKey: Send, Sync);
+    static_assertions::assert_not_impl_any!(LuaRef: Send);
+
+    #[cfg(feature = "unstable")]
+    static_assertions::assert_not_impl_any!(LuaOwnedRef: Send);
+}

src/userdata_ext.rs

@@ -0,0 +1,205 @@
+use crate::error::{Error, Result};
+use crate::private::Sealed;
+use crate::userdata::{AnyUserData, MetaMethod};
+use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, Value};
+
+#[cfg(feature = "async")]
+use futures_util::future::{self, LocalBoxFuture};
+
+/// An extension trait for [`AnyUserData`] that provides a variety of convenient functionality.
+pub trait AnyUserDataExt<'lua>: Sealed {
+    /// Gets the value associated to `key` from the userdata, assuming it has `__index` metamethod.
+    fn get<K: IntoLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V>;
+
+    /// Sets the value associated to `key` in the userdata, assuming it has `__newindex` metamethod.
+    fn set<K: IntoLua<'lua>, V: IntoLua<'lua>>(&self, key: K, value: V) -> Result<()>;
+
+    /// Calls the userdata as a function assuming it has `__call` metamethod.
+    ///
+    /// The metamethod is called with the userdata as its first argument, followed by the passed arguments.
+    fn call<A, R>(&self, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>;
+
+    /// Asynchronously calls the userdata as a function assuming it has `__call` metamethod.
+    ///
+    /// The metamethod is called with the userdata as its first argument, followed by the passed arguments.
+    #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    fn call_async<'fut, A, R>(&self, args: A) -> LocalBoxFuture<'fut, Result<R>>
+    where
+        'lua: 'fut,
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'fut;
+
+    /// Calls the userdata method, assuming it has `__index` metamethod
+    /// and a function associated to `name`.
+    fn call_method<A, R>(&self, name: impl AsRef<str>, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>;
+
+    /// Gets the function associated to `key` from the table and asynchronously executes it,
+    /// passing the table itself along with `args` as function arguments and returning Future.
+    ///
+    /// Requires `feature = "async"`
+    ///
+    /// This might invoke the `__index` metamethod.
+    #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    fn call_async_method<'fut, A, R>(
+        &self,
+        name: impl AsRef<str>,
+        args: A,
+    ) -> LocalBoxFuture<'fut, Result<R>>
+    where
+        'lua: 'fut,
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'fut;
+
+    /// Gets the function associated to `key` from the table and executes it,
+    /// passing `args` as function arguments.
+    ///
+    /// This is a shortcut for
+    /// `table.get::<_, Function>(key)?.call(args)`
+    ///
+    /// This might invoke the `__index` metamethod.
+    fn call_function<A, R>(&self, name: impl AsRef<str>, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>;
+
+    /// Gets the function associated to `key` from the table and asynchronously executes it,
+    /// passing `args` as function arguments and returning Future.
+    ///
+    /// Requires `feature = "async"`
+    ///
+    /// This might invoke the `__index` metamethod.
+    #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    fn call_async_function<'fut, A, R>(
+        &self,
+        name: impl AsRef<str>,
+        args: A,
+    ) -> LocalBoxFuture<'fut, Result<R>>
+    where
+        'lua: 'fut,
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'fut;
+}
+
+impl<'lua> AnyUserDataExt<'lua> for AnyUserData<'lua> {
+    fn get<K: IntoLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V> {
+        let metatable = self.get_metatable()?;
+        match metatable.get::<Value>(MetaMethod::Index)? {
+            Value::Table(table) => table.raw_get(key),
+            Value::Function(func) => func.call((self.clone(), key)),
+            _ => Err(Error::RuntimeError(
+                "attempt to index a userdata value".to_string(),
+            )),
+        }
+    }
+
+    fn set<K: IntoLua<'lua>, V: IntoLua<'lua>>(&self, key: K, value: V) -> Result<()> {
+        let metatable = self.get_metatable()?;
+        match metatable.get::<Value>(MetaMethod::NewIndex)? {
+            Value::Table(table) => table.raw_set(key, value),
+            Value::Function(func) => func.call((self.clone(), key, value)),
+            _ => Err(Error::RuntimeError(
+                "attempt to index a userdata value".to_string(),
+            )),
+        }
+    }
+
+    fn call<A, R>(&self, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>,
+    {
+        let metatable = self.get_metatable()?;
+        match metatable.get::<Value>(MetaMethod::Call)? {
+            Value::Function(func) => func.call((self.clone(), args)),
+            _ => Err(Error::RuntimeError(
+                "attempt to call a userdata value".to_string(),
+            )),
+        }
+    }
+
+    #[cfg(feature = "async")]
+    fn call_async<'fut, A, R>(&self, args: A) -> LocalBoxFuture<'fut, Result<R>>
+    where
+        'lua: 'fut,
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'fut,
+    {
+        let metatable = match self.get_metatable() {
+            Ok(metatable) => metatable,
+            Err(err) => return Box::pin(future::err(err)),
+        };
+        match metatable.get::<Value>(MetaMethod::Call) {
+            Ok(Value::Function(func)) => func.call_async((self.clone(), args)),
+            Ok(_) => Box::pin(future::err(Error::RuntimeError(
+                "attempt to call a userdata value".to_string(),
+            ))),
+            Err(err) => Box::pin(future::err(err)),
+        }
+    }
+
+    fn call_method<A, R>(&self, name: impl AsRef<str>, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>,
+    {
+        self.call_function(name, (self.clone(), args))
+    }
+
+    #[cfg(feature = "async")]
+    fn call_async_method<'fut, A, R>(
+        &self,
+        name: impl AsRef<str>,
+        args: A,
+    ) -> LocalBoxFuture<'fut, Result<R>>
+    where
+        'lua: 'fut,
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'fut,
+    {
+        self.call_async_function(name, (self.clone(), args))
+    }
+
+    fn call_function<A, R>(&self, name: impl AsRef<str>, args: A) -> Result<R>
+    where
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua>,
+    {
+        match self.get(name.as_ref())? {
+            Value::Function(func) => func.call(args),
+            val => Err(Error::RuntimeError(format!(
+                "attempt to call a {} value",
+                val.type_name()
+            ))),
+        }
+    }
+
+    #[cfg(feature = "async")]
+    fn call_async_function<'fut, A, R>(
+        &self,
+        name: impl AsRef<str>,
+        args: A,
+    ) -> LocalBoxFuture<'fut, Result<R>>
+    where
+        'lua: 'fut,
+        A: IntoLuaMulti<'lua>,
+        R: FromLuaMulti<'lua> + 'fut,
+    {
+        match self.get(name.as_ref()) {
+            Ok(Value::Function(func)) => func.call_async(args),
+            Ok(val) => Box::pin(future::err(Error::RuntimeError(format!(
+                "attempt to call a {} value",
+                val.type_name()
+            )))),
+            Err(err) => Box::pin(future::err(err)),
+        }
+    }
+}

src/util/mod.rs

@@ -11,7 +11,9 @@ use once_cell::sync::Lazy;
 use rustc_hash::FxHashMap;
 
 use crate::error::{Error, Result};
-use crate::ffi;
+use crate::memory::MemoryState;
+
+pub(crate) use short_names::short_type_name;
 
 static METATABLE_CACHE: Lazy<FxHashMap<TypeId, u8>> = Lazy::new(|| {
     let mut map = FxHashMap::with_capacity_and_hasher(32, Default::default());
@@ -47,7 +49,6 @@ pub unsafe fn check_stack(state: *mut ffi::lua_State, amount: c_int) -> Result<(
 pub struct StackGuard {
     state: *mut ffi::lua_State,
     top: c_int,
-    extra: c_int,
 }
 
 impl StackGuard {
@@ -59,17 +60,6 @@ impl StackGuard {
         StackGuard {
             state,
             top: ffi::lua_gettop(state),
-            extra: 0,
-        }
-    }
-
-    // Similar to `new`, but checks and keeps `extra` elements from top of the stack on Drop.
-    #[inline]
-    pub unsafe fn new_extra(state: *mut ffi::lua_State, extra: c_int) -> StackGuard {
-        StackGuard {
-            state,
-            top: ffi::lua_gettop(state),
-            extra,
         }
     }
 }
@@ -78,14 +68,11 @@ impl Drop for StackGuard {
     fn drop(&mut self) {
         unsafe {
             let top = ffi::lua_gettop(self.state);
-            if top < self.top + self.extra {
+            if top < self.top {
                 mlua_panic!("{} too many stack values popped", self.top - top)
             }
-            if top > self.top + self.extra {
-                if self.extra > 0 {
-                    ffi::lua_rotate(self.state, self.top + 1, self.extra);
-                }
-                ffi::lua_settop(self.state, self.top + self.extra);
+            if top > self.top {
+                ffi::lua_settop(self.state, self.top);
             }
         }
     }
@@ -104,8 +91,10 @@ pub unsafe fn protect_lua_call(
 ) -> Result<()> {
     let stack_start = ffi::lua_gettop(state) - nargs;
 
-    ffi::lua_pushcfunction(state, error_traceback);
-    ffi::lua_pushcfunction(state, f);
+    MemoryState::relax_limit_with(state, || {
+        ffi::lua_pushcfunction(state, error_traceback);
+        ffi::lua_pushcfunction(state, f);
+    });
     if nargs > 0 {
         ffi::lua_rotate(state, stack_start + 1, 2);
     }
@@ -162,8 +151,10 @@ where
 
     let stack_start = ffi::lua_gettop(state) - nargs;
 
-    ffi::lua_pushcfunction(state, error_traceback);
-    ffi::lua_pushcfunction(state, do_call::<F, R>);
+    MemoryState::relax_limit_with(state, || {
+        ffi::lua_pushcfunction(state, error_traceback);
+        ffi::lua_pushcfunction(state, do_call::<F, R>);
+    });
     if nargs > 0 {
         ffi::lua_rotate(state, stack_start + 1, 2);
     }
@@ -273,11 +264,7 @@ pub unsafe fn push_table(
 }
 
 // Uses 4 stack spaces, does not call checkstack.
-pub unsafe fn rawset_field<S>(state: *mut ffi::lua_State, table: c_int, field: &S) -> Result<()>
-where
-    S: AsRef<[u8]> + ?Sized,
-{
-    let field = field.as_ref();
+pub unsafe fn rawset_field(state: *mut ffi::lua_State, table: c_int, field: &str) -> Result<()> {
     ffi::lua_pushvalue(state, table);
     protect_lua!(state, 2, 0, |state| {
         ffi::lua_pushlstring(state, field.as_ptr() as *const c_char, field.len());
@@ -415,9 +402,12 @@ unsafe extern "C" fn lua_error_impl(state: *mut ffi::lua_State) -> c_int {
 }
 
 unsafe extern "C" fn lua_isfunction_impl(state: *mut ffi::lua_State) -> c_int {
-    let t = ffi::lua_type(state, -1);
-    ffi::lua_pop(state, 1);
-    ffi::lua_pushboolean(state, (t == ffi::LUA_TFUNCTION) as c_int);
+    ffi::lua_pushboolean(state, ffi::lua_isfunction(state, -1));
+    1
+}
+
+unsafe extern "C" fn lua_istable_impl(state: *mut ffi::lua_State) -> c_int {
+    ffi::lua_pushboolean(state, ffi::lua_istable(state, -1));
     1
 }
 
@@ -431,14 +421,19 @@ unsafe fn init_userdata_metatable_index(state: *mut ffi::lua_State) -> Result<()
     // Create and cache `__index` generator
     let code = cstr!(
         r#"
-            local error, isfunction = ...
+            local error, isfunction, istable = ...
             return function (__index, field_getters, methods)
-                -- Fastpath to return methods table for index access
-                if __index == nil and field_getters == nil then
-                    return methods
+                -- Common case: has field getters and index is a table
+                if field_getters ~= nil and methods == nil and istable(__index) then
+                    return function (self, key)
+                        local field_getter = field_getters[key]
+                        if field_getter ~= nil then
+                            return field_getter(self)
+                        end
+                        return __index[key]
+                    end
                 end
 
-                -- Alternatively return a function for index access
                 return function (self, key)
                     if field_getters ~= nil then
                         local field_getter = field_getters[key]
@@ -473,7 +468,13 @@ unsafe fn init_userdata_metatable_index(state: *mut ffi::lua_State) -> Result<()
         }
         ffi::lua_pushcfunction(state, lua_error_impl);
         ffi::lua_pushcfunction(state, lua_isfunction_impl);
-        ffi::lua_call(state, 2, 1);
+        ffi::lua_pushcfunction(state, lua_istable_impl);
+        ffi::lua_call(state, 3, 1);
+
+        #[cfg(feature = "luau-jit")]
+        if ffi::luau_codegen_supported() != 0 {
+            ffi::luau_codegen_compile(state, -1);
+        }
 
         // Store in the registry
         ffi::lua_pushvalue(state, -1);
@@ -523,6 +524,11 @@ pub unsafe fn init_userdata_metatable_newindex(state: *mut ffi::lua_State) -> Re
         ffi::lua_pushcfunction(state, lua_isfunction_impl);
         ffi::lua_call(state, 2, 1);
 
+        #[cfg(feature = "luau-jit")]
+        if ffi::luau_codegen_supported() != 0 {
+            ffi::luau_codegen_compile(state, -1);
+        }
+
         // Store in the registry
         ffi::lua_pushvalue(state, -1);
         ffi::lua_rawsetp(state, ffi::LUA_REGISTRYINDEX, newindex_key);
@@ -681,6 +687,13 @@ where
 }
 
 pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
+    // Luau calls error handler for memory allocation errors, skip it
+    // See https://github.com/Roblox/luau/issues/880
+    #[cfg(feature = "luau")]
+    if MemoryState::limit_reached(state) {
+        return 0;
+    }
+
     if ffi::lua_checkstack(state, 2) == 0 {
         // If we don't have enough stack space to even check the error type, do
         // nothing so we don't risk shadowing a rust panic.
@@ -869,7 +882,7 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) -> Result<()> {
                     // Depending on how the API is used and what error types scripts are given, it may
                     // be possible to make this consume arbitrary amounts of memory (for example, some
                     // kind of recursive error structure?)
-                    let _ = write!(&mut (*err_buf), "{}", error);
+                    let _ = write!(&mut (*err_buf), "{error}");
                     Ok(err_buf)
                 }
                 Some(WrappedFailure::Panic(Some(ref panic))) => {
@@ -880,9 +893,9 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) -> Result<()> {
                     ffi::lua_pop(state, 2);
 
                     if let Some(msg) = panic.downcast_ref::<&str>() {
-                        let _ = write!(&mut (*err_buf), "{}", msg);
+                        let _ = write!(&mut (*err_buf), "{msg}");
                     } else if let Some(msg) = panic.downcast_ref::<String>() {
-                        let _ = write!(&mut (*err_buf), "{}", msg);
+                        let _ = write!(&mut (*err_buf), "{msg}");
                     } else {
                         let _ = write!(&mut (*err_buf), "<panic>");
                     };
@@ -1031,7 +1044,7 @@ pub(crate) unsafe fn to_string(state: *mut ffi::lua_State, index: c_int) -> Stri
             let v = ffi::lua_tovector(state, index);
             mlua_debug_assert!(!v.is_null(), "vector is null");
             let (x, y, z) = (*v, *v.add(1), *v.add(2));
-            format!("vector({},{},{})", x, y, z)
+            format!("vector({x},{y},{z})")
         }
         ffi::LUA_TSTRING => {
             let mut size = 0;
@@ -1064,3 +1077,5 @@ static DESTRUCTED_USERDATA_METATABLE: u8 = 0;
 static ERROR_PRINT_BUFFER_KEY: u8 = 0;
 static USERDATA_METATABLE_INDEX: u8 = 0;
 static USERDATA_METATABLE_NEWINDEX: u8 = 0;
+
+mod short_names;

src/util/short_names.rs

@@ -0,0 +1,84 @@
+//! Mostly copied from bevy_utils
+//! https://github.com/bevyengine/bevy/blob/main/crates/bevy_utils/src/short_names.rs
+
+use std::any::type_name;
+
+/// Returns a short version of a type name `T` without all module paths.
+///
+/// The short name of a type is its full name as returned by
+/// [`std::any::type_name`], but with the prefix of all paths removed. For
+/// example, the short name of `alloc::vec::Vec<core::option::Option<u32>>`
+/// would be `Vec<Option<u32>>`.
+pub(crate) fn short_type_name<T: ?Sized>() -> String {
+    let full_name = type_name::<T>();
+
+    // Generics result in nested paths within <..> blocks.
+    // Consider "core::option::Option<alloc::string::String>".
+    // To tackle this, we parse the string from left to right, collapsing as we go.
+    let mut index: usize = 0;
+    let end_of_string = full_name.len();
+    let mut parsed_name = String::new();
+
+    while index < end_of_string {
+        let rest_of_string = full_name.get(index..end_of_string).unwrap_or_default();
+
+        // Collapse everything up to the next special character,
+        // then skip over it
+        if let Some(special_character_index) = rest_of_string
+            .find(|c: char| [' ', '<', '>', '(', ')', '[', ']', ',', ';'].contains(&c))
+        {
+            let segment_to_collapse = rest_of_string
+                .get(0..special_character_index)
+                .unwrap_or_default();
+            parsed_name += collapse_type_name(segment_to_collapse);
+            // Insert the special character
+            let special_character =
+                &rest_of_string[special_character_index..=special_character_index];
+            parsed_name.push_str(special_character);
+
+            match special_character {
+                ">" | ")" | "]"
+                    if rest_of_string[special_character_index + 1..].starts_with("::") =>
+                {
+                    parsed_name.push_str("::");
+                    // Move the index past the "::"
+                    index += special_character_index + 3;
+                }
+                // Move the index just past the special character
+                _ => index += special_character_index + 1,
+            }
+        } else {
+            // If there are no special characters left, we're done!
+            parsed_name += collapse_type_name(rest_of_string);
+            index = end_of_string;
+        }
+    }
+    parsed_name
+}
+
+#[inline(always)]
+fn collapse_type_name(string: &str) -> &str {
+    string.rsplit("::").next().unwrap()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::short_type_name;
+    use std::collections::HashMap;
+
+    #[test]
+    fn tests() {
+        assert_eq!(short_type_name::<String>(), "String");
+        assert_eq!(short_type_name::<Option<String>>(), "Option<String>");
+        assert_eq!(short_type_name::<(String, &str)>(), "(String, &str)");
+        assert_eq!(short_type_name::<[i32; 3]>(), "[i32; 3]");
+        assert_eq!(
+            short_type_name::<HashMap<String, Option<[i32; 3]>>>(),
+            "HashMap<String, Option<[i32; 3]>>"
+        );
+        assert_eq!(
+            short_type_name::<dyn Fn(i32) -> i32>(),
+            "dyn Fn(i32) -> i32"
+        );
+    }
+}

src/value.rs

@@ -1,7 +1,11 @@
+use std::cmp::Ordering;
+use std::collections::HashSet;
 use std::iter::{self, FromIterator};
 use std::ops::Index;
 use std::os::raw::c_void;
-use std::{ptr, slice, str, vec};
+use std::string::String as StdString;
+use std::sync::Arc;
+use std::{fmt, ptr, slice, str, vec};
 
 #[cfg(feature = "serialize")]
 use {
@@ -11,7 +15,6 @@ use {
 };
 
 use crate::error::{Error, Result};
-use crate::ffi;
 use crate::function::Function;
 use crate::lua::Lua;
 use crate::string::String;
@@ -19,11 +22,12 @@ use crate::table::Table;
 use crate::thread::Thread;
 use crate::types::{Integer, LightUserData, Number};
 use crate::userdata::AnyUserData;
+use crate::util::{check_stack, StackGuard};
 
 /// A dynamically typed Lua value. The `String`, `Table`, `Function`, `Thread`, and `UserData`
 /// variants contain handle types into the internal Lua state. It is a logic error to mix handle
 /// types between separate `Lua` instances, and doing so will result in a panic.
-#[derive(Debug, Clone)]
+#[derive(Clone)]
 pub enum Value<'lua> {
     /// The Lua value `nil`.
     Nil,
@@ -61,6 +65,12 @@ pub enum Value<'lua> {
 pub use self::Value::Nil;
 
 impl<'lua> Value<'lua> {
+    /// A special value (lightuserdata) to represent null value.
+    ///
+    /// It can be used in Lua tables without downsides of `nil`.
+    pub const NULL: Value<'static> = Value::LightUserData(LightUserData(ptr::null_mut()));
+
+    /// Returns type name of this value.
     pub const fn type_name(&self) -> &'static str {
         match *self {
             Value::Nil => "nil",
@@ -93,7 +103,7 @@ impl<'lua> Value<'lua> {
         match (self, other.as_ref()) {
             (Value::Table(a), Value::Table(b)) => a.equals(b),
             (Value::UserData(a), Value::UserData(b)) => a.equals(b),
-            _ => Ok(self == other.as_ref()),
+            (a, b) => Ok(a == b),
         }
     }
 
@@ -120,6 +130,134 @@ impl<'lua> Value<'lua> {
             }
         }
     }
+
+    /// Converts the value to a string.
+    ///
+    /// If the value has a metatable with a `__tostring` method, then it will be called to get the result.
+    pub fn to_string(&self) -> Result<StdString> {
+        match self {
+            Value::Nil => Ok("nil".to_string()),
+            Value::Boolean(b) => Ok(b.to_string()),
+            Value::LightUserData(ud) if ud.0.is_null() => Ok("null".to_string()),
+            Value::LightUserData(ud) => Ok(format!("lightuserdata: {:p}", ud.0)),
+            Value::Integer(i) => Ok(i.to_string()),
+            Value::Number(n) => Ok(n.to_string()),
+            #[cfg(feature = "luau")]
+            Value::Vector(x, y, z) => Ok(format!("vector({x}, {y}, {z})")),
+            Value::String(s) => Ok(s.to_str()?.to_string()),
+            Value::Table(Table(r))
+            | Value::Function(Function(r))
+            | Value::Thread(Thread(r))
+            | Value::UserData(AnyUserData(r)) => unsafe {
+                let state = r.lua.state();
+                let _guard = StackGuard::new(state);
+                check_stack(state, 3)?;
+
+                r.lua.push_ref(r);
+                protect_lua!(state, 1, 1, fn(state) {
+                    ffi::luaL_tolstring(state, -1, ptr::null_mut());
+                })?;
+                Ok(String(r.lua.pop_ref()).to_str()?.to_string())
+            },
+            Value::Error(err) => Ok(err.to_string()),
+        }
+    }
+
+    // Compares two values.
+    // Used to sort values for Debug printing.
+    pub(crate) fn cmp(&self, other: &Self) -> Ordering {
+        fn cmp_num(a: Number, b: Number) -> Ordering {
+            match (a, b) {
+                _ if a < b => Ordering::Less,
+                _ if a > b => Ordering::Greater,
+                _ => Ordering::Equal,
+            }
+        }
+
+        match (self, other) {
+            // Nil
+            (Value::Nil, Value::Nil) => Ordering::Equal,
+            (Value::Nil, _) => Ordering::Less,
+            (_, Value::Nil) => Ordering::Greater,
+            // Null (a special case)
+            (Value::LightUserData(ud1), Value::LightUserData(ud2)) if ud1 == ud2 => Ordering::Equal,
+            (Value::LightUserData(ud1), _) if ud1.0.is_null() => Ordering::Less,
+            (_, Value::LightUserData(ud2)) if ud2.0.is_null() => Ordering::Greater,
+            // Boolean
+            (Value::Boolean(a), Value::Boolean(b)) => a.cmp(b),
+            (Value::Boolean(_), _) => Ordering::Less,
+            (_, Value::Boolean(_)) => Ordering::Greater,
+            // Integer && Number
+            (Value::Integer(a), Value::Integer(b)) => a.cmp(b),
+            (&Value::Integer(a), &Value::Number(b)) => cmp_num(a as Number, b),
+            (&Value::Number(a), &Value::Integer(b)) => cmp_num(a, b as Number),
+            (&Value::Number(a), &Value::Number(b)) => cmp_num(a, b),
+            (Value::Integer(_) | Value::Number(_), _) => Ordering::Less,
+            (_, Value::Integer(_) | Value::Number(_)) => Ordering::Greater,
+            // String
+            (Value::String(a), Value::String(b)) => a.as_bytes().cmp(b.as_bytes()),
+            (Value::String(_), _) => Ordering::Less,
+            (_, Value::String(_)) => Ordering::Greater,
+            // Other variants can be randomly ordered
+            (a, b) => a.to_pointer().cmp(&b.to_pointer()),
+        }
+    }
+
+    pub(crate) fn fmt_pretty(
+        &self,
+        fmt: &mut fmt::Formatter,
+        recursive: bool,
+        ident: usize,
+        visited: &mut HashSet<*const c_void>,
+    ) -> fmt::Result {
+        match self {
+            Value::Nil => write!(fmt, "nil"),
+            Value::Boolean(b) => write!(fmt, "{b}"),
+            Value::LightUserData(ud) if ud.0.is_null() => write!(fmt, "null"),
+            Value::LightUserData(ud) => write!(fmt, "lightuserdata: {:?}", ud.0),
+            Value::Integer(i) => write!(fmt, "{i}"),
+            Value::Number(n) => write!(fmt, "{n}"),
+            #[cfg(feature = "luau")]
+            Value::Vector(x, y, z) => write!(fmt, "vector({x}, {y}, {z})"),
+            Value::String(s) => write!(fmt, "{s:?}"),
+            Value::Table(t) if recursive && !visited.contains(&t.to_pointer()) => {
+                t.fmt_pretty(fmt, ident, visited)
+            }
+            t @ Value::Table(_) => write!(fmt, "table: {:?}", t.to_pointer()),
+            f @ Value::Function(_) => write!(fmt, "function: {:?}", f.to_pointer()),
+            t @ Value::Thread(_) => write!(fmt, "thread: {:?}", t.to_pointer()),
+            u @ Value::UserData(ud) => {
+                let name = ud.type_name().ok().flatten();
+                let name = name.unwrap_or_else(|| "userdata".to_string());
+                write!(fmt, "{name}: {:?}", u.to_pointer())
+            }
+            Value::Error(e) if recursive => write!(fmt, "{e:?}"),
+            Value::Error(_) => write!(fmt, "error"),
+        }
+    }
+}
+
+impl fmt::Debug for Value<'_> {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        if fmt.alternate() {
+            return self.fmt_pretty(fmt, true, 0, &mut HashSet::new());
+        }
+        match self {
+            Value::Nil => write!(fmt, "Nil"),
+            Value::Boolean(b) => write!(fmt, "Boolean({b})"),
+            Value::LightUserData(ud) => write!(fmt, "{ud:?}"),
+            Value::Integer(i) => write!(fmt, "Integer({i})"),
+            Value::Number(n) => write!(fmt, "Number({n})"),
+            #[cfg(feature = "luau")]
+            Value::Vector(x, y, z) => write!(fmt, "Vector({x}, {y}, {z})"),
+            Value::String(s) => write!(fmt, "String({s:?})"),
+            Value::Table(t) => write!(fmt, "{t:?}"),
+            Value::Function(f) => write!(fmt, "{f:?}"),
+            Value::Thread(t) => write!(fmt, "{t:?}"),
+            Value::UserData(ud) => write!(fmt, "{ud:?}"),
+            Value::Error(e) => write!(fmt, "Error({e:?})"),
+        }
+    }
 }
 
 impl<'lua> PartialEq for Value<'lua> {
@@ -162,8 +300,7 @@ impl<'lua> Serialize for Value<'lua> {
             Value::Boolean(b) => serializer.serialize_bool(*b),
             #[allow(clippy::useless_conversion)]
             Value::Integer(i) => serializer
-                .serialize_i64((*i).try_into().expect("cannot convert lua_Integer to i64")),
-            #[allow(clippy::useless_conversion)]
+                .serialize_i64((*i).try_into().expect("cannot convert Lua Integer to i64")),
             Value::Number(n) => serializer.serialize_f64(*n),
             #[cfg(feature = "luau")]
             Value::Vector(x, y, z) => (x, y, z).serialize(serializer),
@@ -180,15 +317,34 @@ impl<'lua> Serialize for Value<'lua> {
 }
 
 /// Trait for types convertible to `Value`.
-pub trait ToLua<'lua> {
+pub trait IntoLua<'lua> {
     /// Performs the conversion.
-    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>>;
+    fn into_lua(self, lua: &'lua Lua) -> Result<Value<'lua>>;
 }
 
 /// Trait for types convertible from `Value`.
 pub trait FromLua<'lua>: Sized {
     /// Performs the conversion.
-    fn from_lua(lua_value: Value<'lua>, lua: &'lua Lua) -> Result<Self>;
+    fn from_lua(value: Value<'lua>, lua: &'lua Lua) -> Result<Self>;
+
+    /// Performs the conversion for an argument (eg. function argument).
+    ///
+    /// `i` is the argument index (position),
+    /// `to` is a function name that received the argument.
+    #[doc(hidden)]
+    fn from_lua_arg(
+        value: Value<'lua>,
+        i: usize,
+        to: Option<&str>,
+        lua: &'lua Lua,
+    ) -> Result<Self> {
+        Self::from_lua(value, lua).map_err(|err| Error::BadArgument {
+            to: to.map(|s| s.to_string()),
+            pos: i,
+            name: None,
+            cause: Arc::new(err),
+        })
+    }
 }
 
 /// Multiple Lua values used for both argument passing and also for multiple return values.
@@ -203,8 +359,14 @@ impl<'lua> MultiValue<'lua> {
 
     /// Similar to `new` but can return previously used container with allocated capacity.
     #[inline]
-    pub(crate) fn new_or_cached(lua: &'lua Lua) -> MultiValue<'lua> {
-        lua.new_or_cached_multivalue()
+    pub(crate) fn new_or_pooled(lua: &'lua Lua) -> MultiValue<'lua> {
+        lua.new_multivalue_from_pool()
+    }
+
+    /// Clears and returns previously allocated multivalue container to the pool.
+    #[inline]
+    pub(crate) fn return_to_pool(multivalue: Self, lua: &Lua) {
+        lua.return_multivalue_to_pool(multivalue);
     }
 }
 
@@ -337,11 +499,11 @@ impl<'lua> MultiValue<'lua> {
 
 /// Trait for types convertible to any number of Lua values.
 ///
-/// This is a generalization of `ToLua`, allowing any number of resulting Lua values instead of just
-/// one. Any type that implements `ToLua` will automatically implement this trait.
-pub trait ToLuaMulti<'lua> {
+/// This is a generalization of `IntoLua`, allowing any number of resulting Lua values instead of just
+/// one. Any type that implements `IntoLua` will automatically implement this trait.
+pub trait IntoLuaMulti<'lua> {
     /// Performs the conversion.
-    fn to_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>>;
+    fn into_lua_multi(self, lua: &'lua Lua) -> Result<MultiValue<'lua>>;
 }
 
 /// Trait for types that can be created from an arbitrary number of Lua values.
@@ -356,4 +518,28 @@ pub trait FromLuaMulti<'lua>: Sized {
     /// assigning values. Similarly, if not enough values are given, conversions should assume that
     /// any missing values are nil.
     fn from_lua_multi(values: MultiValue<'lua>, lua: &'lua Lua) -> Result<Self>;
+
+    /// Performs the conversion for a list of arguments.
+    ///
+    /// `i` is an index (position) of the first argument,
+    /// `to` is a function name that received the arguments.
+    #[doc(hidden)]
+    #[inline]
+    fn from_lua_multi_args(
+        values: MultiValue<'lua>,
+        i: usize,
+        to: Option<&str>,
+        lua: &'lua Lua,
+    ) -> Result<Self> {
+        let _ = (i, to);
+        Self::from_lua_multi(values, lua)
+    }
+}
+
+#[cfg(test)]
+mod assertions {
+    use super::*;
+
+    static_assertions::assert_not_impl_any!(Value: Send);
+    static_assertions::assert_not_impl_any!(MultiValue: Send);
 }

tarpaulin.toml

@@ -1,8 +1,8 @@
 [lua54_coverage]
-features = "lua54,vendored,async,serialize,macros"
+features = "lua54,vendored,async,serialize,macros,unstable"
 
 [lua51_coverage]
-features = "lua51,vendored,async,serialize,macros"
+features = "lua51,vendored,async,serialize,macros,unstable"
 
 [luau_coverage]
-features = "luau,async,serialize,macros"
+features = "luau,async,serialize,macros,unstable"

tests/async.rs

@@ -1,18 +1,14 @@
 #![cfg(feature = "async")]
 
-use std::cell::Cell;
-use std::rc::Rc;
-use std::sync::{
-    atomic::{AtomicI64, AtomicU64, Ordering},
-    Arc,
-};
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::{Arc, Mutex};
 use std::time::Duration;
 
 use futures_timer::Delay;
 use futures_util::stream::TryStreamExt;
 
 use mlua::{
-    Error, Function, Lua, LuaOptions, Result, StdLib, Table, TableExt, Thread, UserData,
+    AnyUserDataExt, Error, Function, Lua, LuaOptions, Result, StdLib, Table, TableExt, UserData,
     UserDataMethods, Value,
 };
 
@@ -30,6 +26,19 @@ async fn test_async_function() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn test_async_function_wrap() -> Result<()> {
+    let lua = Lua::new();
+
+    let f = Function::wrap_async(|_, s: String| async move { Ok(s) });
+    lua.globals().set("f", f)?;
+
+    let res: String = lua.load(r#"f("hello")"#).eval_async().await?;
+    assert_eq!(res, "hello");
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_async_sleep() -> Result<()> {
     let lua = Lua::new();
@@ -261,9 +270,27 @@ async fn test_async_thread() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_async_thread_capture() -> Result<()> {
+    let lua = Lua::new();
+
+    let f = lua.create_async_function(move |_lua, v: Value| async move {
+        tokio::task::yield_now().await;
+        drop(v);
+        Ok(())
+    })?;
+
+    let thread = lua.create_thread(f)?;
+    // After first resume, `v: Value` is captured in the coroutine
+    thread.resume::<_, ()>("abc").unwrap();
+    drop(thread);
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_async_table() -> Result<()> {
-    let options = LuaOptions::new().thread_cache_size(4);
+    let options = LuaOptions::new().thread_pool_size(4);
     let lua = Lua::new_with(StdLib::ALL_SAFE, options)?;
 
     let table = lua.create_table()?;
@@ -311,8 +338,8 @@ async fn test_async_table() -> Result<()> {
 }
 
 #[tokio::test]
-async fn test_async_thread_cache() -> Result<()> {
-    let options = LuaOptions::new().thread_cache_size(4);
+async fn test_async_thread_pool() -> Result<()> {
+    let options = LuaOptions::new().thread_pool_size(4);
     let lua = Lua::new_with(StdLib::ALL_SAFE, options)?;
 
     let error_f = lua.create_async_function(|_, ()| async move {
@@ -423,6 +450,14 @@ async fn test_async_userdata() -> Result<()> {
     .exec_async()
     .await?;
 
+    userdata.call_async_method("set_value", 24).await?;
+    let n: u64 = userdata.call_async_method("get_value", ()).await?;
+    assert_eq!(n, 24);
+    userdata.call_async_function("sleep", 15).await?;
+
+    #[cfg(not(any(feature = "lua51", feature = "luau")))]
+    assert_eq!(userdata.call_async::<_, String>(()).await?, "elapsed:24ms");
+
     Ok(())
 }
 
@@ -439,7 +474,7 @@ async fn test_async_thread_error() -> Result<()> {
     let lua = Lua::new();
     let result = lua
         .load("function x(...) error(...) end x(...)")
-        .set_name("chunk")?
+        .set_name("chunk")
         .call_async::<_, ()>(MyUserData)
         .await;
     assert!(
@@ -450,120 +485,42 @@ async fn test_async_thread_error() -> Result<()> {
     Ok(())
 }
 
+#[cfg(all(feature = "unstable", not(feature = "send")))]
 #[tokio::test]
-async fn test_async_scope() -> Result<()> {
-    let ref lua = Lua::new();
+async fn test_owned_async_call() -> Result<()> {
+    let lua = Lua::new();
 
-    let ref rc = Rc::new(Cell::new(0));
+    let hello = lua
+        .create_async_function(|_, name: String| async move {
+            Delay::new(Duration::from_millis(10)).await;
+            Ok(format!("hello, {}!", name))
+        })?
+        .into_owned();
+    drop(lua);
 
-    let fut = lua.async_scope(|scope| async move {
-        let f = scope.create_async_function(move |_, n: u64| {
-            let rc2 = rc.clone();
-            async move {
-                rc2.set(42);
-                Delay::new(Duration::from_millis(n)).await;
-                assert_eq!(Rc::strong_count(&rc2), 2);
-                Ok(())
-            }
-        })?;
-
-        lua.globals().set("f", f.clone())?;
-
-        assert_eq!(Rc::strong_count(rc), 1);
-        let _ = f.call_async::<u64, ()>(10).await?;
-        assert_eq!(Rc::strong_count(rc), 1);
-
-        // Create future in partialy polled state (Poll::Pending)
-        let g = lua.create_thread(f)?;
-        g.resume::<u64, ()>(10)?;
-        lua.globals().set("g", g)?;
-        assert_eq!(Rc::strong_count(rc), 2);
-
-        Ok(())
-    });
-
-    assert_eq!(Rc::strong_count(rc), 1);
-    let _ = fut.await?;
-    assert_eq!(Rc::strong_count(rc), 1);
-
-    match lua
-        .globals()
-        .get::<_, Function>("f")?
-        .call_async::<_, ()>(10)
-        .await
-    {
-        Err(Error::CallbackError { ref cause, .. }) => match cause.as_ref() {
-            Error::CallbackDestructed => {}
-            e => panic!("expected `CallbackDestructed` error cause, got {:?}", e),
-        },
-        r => panic!("improper return for destructed function: {:?}", r),
-    };
-
-    match lua.globals().get::<_, Thread>("g")?.resume::<_, Value>(()) {
-        Err(Error::CallbackError { ref cause, .. }) => match cause.as_ref() {
-            Error::CallbackDestructed => {}
-            e => panic!("expected `CallbackDestructed` error cause, got {:?}", e),
-        },
-        r => panic!("improper return for destructed function: {:?}", r),
-    };
+    assert_eq!(hello.call_async::<_, String>("alex").await?, "hello, alex!");
 
     Ok(())
 }
 
 #[tokio::test]
-async fn test_async_scope_userdata() -> Result<()> {
-    #[derive(Clone)]
-    struct MyUserData(Arc<AtomicI64>);
+async fn test_async_terminate() -> Result<()> {
+    let lua = Lua::new();
 
-    impl UserData for MyUserData {
-        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
-            methods.add_async_method("get_value", |_, data, ()| async move {
-                Delay::new(Duration::from_millis(10)).await;
-                Ok(data.0.load(Ordering::Relaxed))
-            });
-
-            methods.add_async_method("set_value", |_, data, n| async move {
-                Delay::new(Duration::from_millis(10)).await;
-                data.0.store(n, Ordering::Relaxed);
-                Ok(())
-            });
-
-            methods.add_async_function("sleep", |_, n| async move {
-                Delay::new(Duration::from_millis(n)).await;
-                Ok(format!("elapsed:{}ms", n))
-            });
+    let mutex = Arc::new(Mutex::new(0u32));
+    let mutex2 = mutex.clone();
+    let func = lua.create_async_function(move |_, ()| {
+        let mutex = mutex2.clone();
+        async move {
+            let _guard = mutex.lock();
+            Delay::new(Duration::from_millis(100)).await;
+            Ok(())
         }
-    }
+    })?;
 
-    let ref lua = Lua::new();
-
-    let ref arc = Arc::new(AtomicI64::new(11));
-
-    lua.async_scope(|scope| async move {
-        let ud = scope.create_userdata(MyUserData(arc.clone()))?;
-        lua.globals().set("userdata", ud)?;
-        lua.load(
-            r#"
-            assert(userdata:get_value() == 11)
-            userdata:set_value(12)
-            assert(userdata.sleep(5) == "elapsed:5ms")
-            assert(userdata:get_value() == 12)
-        "#,
-        )
-        .exec_async()
-        .await
-    })
-    .await?;
-
-    assert_eq!(Arc::strong_count(arc), 1);
-
-    match lua.load("userdata:get_value()").exec_async().await {
-        Err(Error::CallbackError { ref cause, .. }) => match cause.as_ref() {
-            Error::CallbackDestructed => {}
-            e => panic!("expected `CallbackDestructed` error cause, got {:?}", e),
-        },
-        r => panic!("improper return for destructed userdata: {:?}", r),
-    };
+    let _ = tokio::time::timeout(Duration::from_millis(30), func.call_async::<_, ()>(())).await;
+    lua.gc_collect()?;
+    assert!(mutex.try_lock().is_ok());
 
     Ok(())
 }

tests/chunk.rs

@@ -1,7 +1,7 @@
 use std::fs;
 use std::io;
 
-use mlua::{Error, Lua, Result};
+use mlua::{Lua, Result};
 
 #[test]
 fn test_chunk_path() -> Result<()> {
@@ -14,12 +14,11 @@ fn test_chunk_path() -> Result<()> {
         return 321
     "#,
     )?;
-    let i: i32 = lua.load(&temp_dir.path().join("module.lua")).eval()?;
+    let i: i32 = lua.load(&*temp_dir.path().join("module.lua")).eval()?;
     assert_eq!(i, 321);
 
-    match lua.load(&temp_dir.path().join("module2.lua")).exec() {
-        Err(Error::ExternalError(err))
-            if err.downcast_ref::<io::Error>().unwrap().kind() == io::ErrorKind::NotFound => {}
+    match lua.load(&*temp_dir.path().join("module2.lua")).exec() {
+        Err(err) if err.downcast_ref::<io::Error>().unwrap().kind() == io::ErrorKind::NotFound => {}
         res => panic!("expected io::Error, got {:?}", res),
     };
 

tests/compile/lua_norefunwindsafe.stderr

@@ -1,22 +1,28 @@
-error[E0277]: the type `UnsafeCell<mlua::lua::LuaInner>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
-   --> tests/compile/lua_norefunwindsafe.rs:7:5
-    |
-7   |     catch_unwind(|| lua.create_table().unwrap());
-    |     ^^^^^^^^^^^^ `UnsafeCell<mlua::lua::LuaInner>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
-    |
-    = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<mlua::lua::LuaInner>`
-    = note: required because it appears within the type `alloc::sync::ArcInner<UnsafeCell<mlua::lua::LuaInner>>`
-    = note: required because it appears within the type `PhantomData<alloc::sync::ArcInner<UnsafeCell<mlua::lua::LuaInner>>>`
-    = note: required because it appears within the type `Arc<UnsafeCell<mlua::lua::LuaInner>>`
-    = note: required because it appears within the type `Lua`
-    = note: required because of the requirements on the impl of `UnwindSafe` for `&Lua`
+error[E0277]: the type `UnsafeCell<mlua::lua::ExtraData>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+ --> tests/compile/lua_norefunwindsafe.rs:7:18
+  |
+7 |     catch_unwind(|| lua.create_table().unwrap());
+  |     ------------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<mlua::lua::ExtraData>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+  |     |
+  |     required by a bound introduced by this call
+  |
+  = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<mlua::lua::ExtraData>`
+  = note: required because it appears within the type `ArcInner<UnsafeCell<ExtraData>>`
+  = note: required because it appears within the type `PhantomData<ArcInner<UnsafeCell<ExtraData>>>`
+  = note: required because it appears within the type `Arc<UnsafeCell<ExtraData>>`
+  = note: required because it appears within the type `LuaInner`
+  = note: required because it appears within the type `ArcInner<LuaInner>`
+  = note: required because it appears within the type `PhantomData<ArcInner<LuaInner>>`
+  = note: required because it appears within the type `Arc<LuaInner>`
+  = note: required because it appears within the type `Lua`
+  = note: required for `&Lua` to implement `UnwindSafe`
 note: required because it's used within this closure
-   --> tests/compile/lua_norefunwindsafe.rs:7:18
-    |
-7   |     catch_unwind(|| lua.create_table().unwrap());
-    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ --> tests/compile/lua_norefunwindsafe.rs:7:18
+  |
+7 |     catch_unwind(|| lua.create_table().unwrap());
+  |                  ^^
 note: required by a bound in `catch_unwind`
-   --> $RUST/std/src/panic.rs
-    |
-    | pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
-    |                                        ^^^^^^^^^^ required by this bound in `catch_unwind`
+ --> $RUST/std/src/panic.rs
+  |
+  | pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
+  |                                        ^^^^^^^^^^ required by this bound in `catch_unwind`

tests/compile/non_send.stderr

@@ -1,26 +1,25 @@
 error[E0277]: `Rc<Cell<i32>>` cannot be sent between threads safely
-    --> tests/compile/non_send.rs:11:9
-     |
-11   |       lua.create_function(move |_, ()| {
-     |  _________^^^^^^^^^^^^^^^_-
-     | |         |
-     | |         `Rc<Cell<i32>>` cannot be sent between threads safely
-12   | |         Ok(data.get())
-13   | |     })?
-     | |_____- within this `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`
-     |
-     = help: within `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`, the trait `Send` is not implemented for `Rc<Cell<i32>>`
+  --> tests/compile/non_send.rs:11:25
+   |
+11 |       lua.create_function(move |_, ()| {
+   |           --------------- ^-----------
+   |           |               |
+   |  _________|_______________within this `[closure@$DIR/tests/compile/non_send.rs:11:25: 11:37]`
+   | |         |
+   | |         required by a bound introduced by this call
+12 | |         Ok(data.get())
+13 | |     })?
+   | |_____^ `Rc<Cell<i32>>` cannot be sent between threads safely
+   |
+   = help: within `[closure@$DIR/tests/compile/non_send.rs:11:25: 11:37]`, the trait `Send` is not implemented for `Rc<Cell<i32>>`
 note: required because it's used within this closure
-    --> tests/compile/non_send.rs:11:25
-     |
-11   |       lua.create_function(move |_, ()| {
-     |  _________________________^
-12   | |         Ok(data.get())
-13   | |     })?
-     | |_____^
-     = note: required because of the requirements on the impl of `mlua::types::MaybeSend` for `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`
+  --> tests/compile/non_send.rs:11:25
+   |
+11 |     lua.create_function(move |_, ()| {
+   |                         ^^^^^^^^^^^^
+   = note: required for `[closure@$DIR/tests/compile/non_send.rs:11:25: 11:37]` to implement `mlua::types::MaybeSend`
 note: required by a bound in `Lua::create_function`
-    --> src/lua.rs
-     |
-     |         F: 'static + MaybeSend + Fn(&'lua Lua, A) -> Result<R>,
-     |                      ^^^^^^^^^ required by this bound in `Lua::create_function`
+  --> src/lua.rs
+   |
+   |         F: 'static + MaybeSend + Fn(&'lua Lua, A) -> Result<R>,
+   |                      ^^^^^^^^^ required by this bound in `Lua::create_function`

tests/compile/ref_nounwindsafe.stderr

@@ -1,24 +1,30 @@
-error[E0277]: the type `UnsafeCell<mlua::lua::LuaInner>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
-   --> tests/compile/ref_nounwindsafe.rs:8:5
-    |
-8   |     catch_unwind(move || table.set("a", "b").unwrap());
-    |     ^^^^^^^^^^^^ `UnsafeCell<mlua::lua::LuaInner>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
-    |
-    = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<mlua::lua::LuaInner>`
-    = note: required because it appears within the type `alloc::sync::ArcInner<UnsafeCell<mlua::lua::LuaInner>>`
-    = note: required because it appears within the type `PhantomData<alloc::sync::ArcInner<UnsafeCell<mlua::lua::LuaInner>>>`
-    = note: required because it appears within the type `Arc<UnsafeCell<mlua::lua::LuaInner>>`
-    = note: required because it appears within the type `Lua`
-    = note: required because of the requirements on the impl of `UnwindSafe` for `&Lua`
-    = note: required because it appears within the type `mlua::types::LuaRef<'_>`
-    = note: required because it appears within the type `LuaTable<'_>`
+error[E0277]: the type `UnsafeCell<mlua::lua::ExtraData>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+ --> tests/compile/ref_nounwindsafe.rs:8:18
+  |
+8 |     catch_unwind(move || table.set("a", "b").unwrap());
+  |     ------------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<mlua::lua::ExtraData>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+  |     |
+  |     required by a bound introduced by this call
+  |
+  = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<mlua::lua::ExtraData>`
+  = note: required because it appears within the type `ArcInner<UnsafeCell<ExtraData>>`
+  = note: required because it appears within the type `PhantomData<ArcInner<UnsafeCell<ExtraData>>>`
+  = note: required because it appears within the type `Arc<UnsafeCell<ExtraData>>`
+  = note: required because it appears within the type `LuaInner`
+  = note: required because it appears within the type `ArcInner<LuaInner>`
+  = note: required because it appears within the type `PhantomData<ArcInner<LuaInner>>`
+  = note: required because it appears within the type `Arc<LuaInner>`
+  = note: required because it appears within the type `Lua`
+  = note: required for `&Lua` to implement `UnwindSafe`
+  = note: required because it appears within the type `LuaRef<'_>`
+  = note: required because it appears within the type `Table<'_>`
 note: required because it's used within this closure
-   --> tests/compile/ref_nounwindsafe.rs:8:18
-    |
-8   |     catch_unwind(move || table.set("a", "b").unwrap());
-    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ --> tests/compile/ref_nounwindsafe.rs:8:18
+  |
+8 |     catch_unwind(move || table.set("a", "b").unwrap());
+  |                  ^^^^^^^
 note: required by a bound in `catch_unwind`
-   --> $RUST/std/src/panic.rs
-    |
-    | pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
-    |                                        ^^^^^^^^^^ required by this bound in `catch_unwind`
+ --> $RUST/std/src/panic.rs
+  |
+  | pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
+  |                                        ^^^^^^^^^^ required by this bound in `catch_unwind`

tests/compile/static_callback_args.stderr

@@ -1,15 +1,17 @@
 error[E0597]: `lua` does not live long enough
   --> tests/compile/static_callback_args.rs:12:5
    |
-12 |  /     lua.create_function(|_, table: Table| {
-13 |  |         BAD_TIME.with(|bt| {
-   |  |_________-
+10 |        let lua = Lua::new();
+   |            --- binding `lua` declared here
+11 |
+12 | /      lua.create_function(|_, table: Table| {
+13 | |/         BAD_TIME.with(|bt| {
 14 | ||             *bt.borrow_mut() = Some(table);
 15 | ||         });
    | ||__________- argument requires that `lua` is borrowed for `'static`
-16 |  |         Ok(())
-17 |  |     })?
-   |  |______^ borrowed value does not live long enough
+16 | |          Ok(())
+17 | |      })?
+   | |_______^ borrowed value does not live long enough
 ...
 32 |    }
    |    - `lua` dropped here while still borrowed
@@ -17,15 +19,17 @@ error[E0597]: `lua` does not live long enough
 error[E0505]: cannot move out of `lua` because it is borrowed
   --> tests/compile/static_callback_args.rs:22:10
    |
-12 |  /     lua.create_function(|_, table: Table| {
-13 |  |         BAD_TIME.with(|bt| {
-   |  |_________-
+10 |        let lua = Lua::new();
+   |            --- binding `lua` declared here
+11 |
+12 | /      lua.create_function(|_, table: Table| {
+13 | |/         BAD_TIME.with(|bt| {
 14 | ||             *bt.borrow_mut() = Some(table);
 15 | ||         });
    | ||__________- argument requires that `lua` is borrowed for `'static`
-16 |  |         Ok(())
-17 |  |     })?
-   |  |______- borrow of `lua` occurs here
+16 | |          Ok(())
+17 | |      })?
+   | |_______- borrow of `lua` occurs here
 ...
 22 |        drop(lua);
    |             ^^^ move out of `lua` occurs here

tests/debug.rs

@@ -0,0 +1,15 @@
+use mlua::{Lua, Result};
+
+#[test]
+fn test_debug_format() -> Result<()> {
+    let lua = Lua::new();
+
+    // Globals
+    let globals = lua.globals();
+    let dump = format!("{globals:#?}");
+    assert!(dump.starts_with("{\n  [\"_G\"] = table:"));
+
+    // TODO: Other cases
+
+    Ok(())
+}

tests/error.rs

@@ -0,0 +1,50 @@
+use std::io;
+
+use mlua::{Error, ErrorContext, Lua, Result};
+
+#[test]
+fn test_error_context() -> Result<()> {
+    let lua = Lua::new();
+
+    let func = lua.create_function(|_, ()| {
+        Err::<(), _>(Error::RuntimeError("runtime error".into())).context("some context")
+    })?;
+    lua.globals().set("func", func)?;
+
+    let msg = lua
+        .load("local _, err = pcall(func); return tostring(err)")
+        .eval::<String>()?;
+    assert!(msg.contains("some context"));
+    assert!(msg.contains("runtime error"));
+
+    let func2 = lua.create_function(|lua, ()| {
+        lua.globals()
+            .get::<_, String>("nonextant")
+            .with_context(|_| "failed to find global")
+    })?;
+    lua.globals().set("func2", func2)?;
+
+    let msg2 = lua
+        .load("local _, err = pcall(func2); return tostring(err)")
+        .eval::<String>()?;
+    assert!(msg2.contains("failed to find global"));
+    println!("{msg2}");
+    assert!(msg2.contains("error converting Lua nil to String"));
+
+    // Rewrite context message and test `downcast_ref`
+    let func3 = lua.create_function(|_, ()| {
+        Err::<(), _>(Error::external(io::Error::new(
+            io::ErrorKind::Other,
+            "other",
+        )))
+        .context("some context")
+        .context("some new context")
+    })?;
+    let res = func3.call::<_, ()>(()).err().unwrap();
+    let Error::CallbackError { cause, .. } = &res else { unreachable!() };
+    assert!(!res.to_string().contains("some context"));
+    assert!(res.to_string().contains("some new context"));
+    assert!(cause.downcast_ref::<io::Error>().is_some());
+
+    Ok(())
+}

tests/function.rs

@@ -1,4 +1,4 @@
-use mlua::{Function, Lua, Result, String};
+use mlua::{Function, Lua, Result, String, Table};
 
 #[test]
 fn test_function() -> Result<()> {
@@ -114,6 +114,66 @@ fn test_dump() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_function_environment() -> Result<()> {
+    let lua = Lua::new();
+
+    // We must not get or set environment for C functions
+    let rust_func = lua.create_function(|_, ()| Ok("hello"))?;
+    assert_eq!(rust_func.environment(), None);
+    assert_eq!(rust_func.set_environment(lua.globals()).ok(), Some(false));
+
+    // Test getting Lua function environment
+    lua.globals().set("hello", "global")?;
+    let lua_func = lua
+        .load(
+            r#"
+        local t = ""
+        return function()
+            -- two upvalues
+            return t .. hello
+        end
+    "#,
+        )
+        .eval::<Function>()?;
+    let lua_func2 = lua.load("return hello").into_function()?;
+    assert_eq!(lua_func.call::<_, String>(())?, "global");
+    assert_eq!(lua_func.environment(), Some(lua.globals()));
+
+    // Test changing the environment
+    let env = lua.create_table_from([("hello", "local")])?;
+    assert!(lua_func.set_environment(env.clone())?);
+    assert_eq!(lua_func.call::<_, String>(())?, "local");
+    assert_eq!(lua_func2.call::<_, String>(())?, "global");
+
+    // More complex case
+    lua.load(
+        r#"
+        local number = 15
+        function lucky() return tostring("number is "..number) end
+        new_env = {
+            tostring = function() return tostring(number) end,
+        }
+    "#,
+    )
+    .exec()?;
+    let lucky = lua.globals().get::<_, Function>("lucky")?;
+    assert_eq!(lucky.call::<_, String>(())?, "number is 15");
+    let new_env = lua.globals().get::<_, Table>("new_env")?;
+    lucky.set_environment(new_env)?;
+    assert_eq!(lucky.call::<_, String>(())?, "15");
+
+    // Test inheritance
+    let lua_func2 = lua
+        .load(r#"return function() return (function() return hello end)() end"#)
+        .eval::<Function>()?;
+    assert!(lua_func2.set_environment(env.clone())?);
+    lua.gc_collect()?;
+    assert_eq!(lua_func2.call::<_, String>(())?, "local");
+
+    Ok(())
+}
+
 #[test]
 fn test_function_info() -> Result<()> {
     let lua = Lua::new();
@@ -126,7 +186,7 @@ fn test_function_info() -> Result<()> {
         end
     "#,
     )
-    .set_name("source1")?
+    .set_name("source1")
     .exec()?;
 
     let function1 = globals.get::<_, Function>("function1")?;
@@ -135,35 +195,112 @@ fn test_function_info() -> Result<()> {
 
     let function1_info = function1.info();
     #[cfg(feature = "luau")]
-    assert_eq!(function1_info.name, Some(b"function1".to_vec()));
-    assert_eq!(function1_info.source, Some(b"source1".to_vec()));
+    assert_eq!(function1_info.name.as_deref(), Some("function1"));
+    assert_eq!(function1_info.source.as_deref(), Some(b"source1".as_ref()));
     assert_eq!(function1_info.line_defined, 2);
     #[cfg(not(feature = "luau"))]
     assert_eq!(function1_info.last_line_defined, 4);
-    assert_eq!(function1_info.what, Some(b"Lua".to_vec()));
+    #[cfg(feature = "luau")]
+    assert_eq!(function1_info.last_line_defined, -1);
+    assert_eq!(function1_info.what.as_deref(), Some("Lua"));
 
     let function2_info = function2.info();
     assert_eq!(function2_info.name, None);
-    assert_eq!(function2_info.source, Some(b"source1".to_vec()));
+    assert_eq!(function2_info.source.as_deref(), Some(b"source1".as_ref()));
     assert_eq!(function2_info.line_defined, 3);
     #[cfg(not(feature = "luau"))]
     assert_eq!(function2_info.last_line_defined, 3);
-    assert_eq!(function2_info.what, Some(b"Lua".to_vec()));
+    #[cfg(feature = "luau")]
+    assert_eq!(function2_info.last_line_defined, -1);
+    assert_eq!(function2_info.what.as_deref(), Some("Lua"));
 
     let function3_info = function3.info();
     assert_eq!(function3_info.name, None);
-    assert_eq!(function3_info.source, Some(b"=[C]".to_vec()));
+    assert_eq!(function3_info.source.as_deref(), Some(b"=[C]".as_ref()));
     assert_eq!(function3_info.line_defined, -1);
-    #[cfg(not(feature = "luau"))]
     assert_eq!(function3_info.last_line_defined, -1);
-    assert_eq!(function3_info.what, Some(b"C".to_vec()));
+    assert_eq!(function3_info.what.as_deref(), Some("C"));
 
     let print_info = globals.get::<_, Function>("print")?.info();
     #[cfg(feature = "luau")]
-    assert_eq!(print_info.name, Some(b"print".to_vec()));
-    assert_eq!(print_info.source, Some(b"=[C]".to_vec()));
-    assert_eq!(print_info.what, Some(b"C".to_vec()));
+    assert_eq!(print_info.name.as_deref(), Some("print"));
+    assert_eq!(print_info.source.as_deref(), Some(b"=[C]".as_ref()));
+    assert_eq!(print_info.what.as_deref(), Some("C"));
     assert_eq!(print_info.line_defined, -1);
 
     Ok(())
 }
+
+#[test]
+fn test_function_wrap() -> Result<()> {
+    use mlua::Error;
+
+    let lua = Lua::new();
+
+    lua.globals()
+        .set("f", Function::wrap(|_, s: String| Ok(s)))?;
+    lua.load(r#"assert(f("hello") == "hello")"#).exec().unwrap();
+
+    let mut _i = false;
+    lua.globals().set(
+        "f",
+        Function::wrap_mut(move |lua, ()| {
+            _i = true;
+            lua.globals().get::<_, Function>("f")?.call::<_, ()>(())
+        }),
+    )?;
+    match lua.globals().get::<_, Function>("f")?.call::<_, ()>(()) {
+        Err(Error::CallbackError { ref cause, .. }) => match *cause.as_ref() {
+            Error::CallbackError { ref cause, .. } => match *cause.as_ref() {
+                Error::RecursiveMutCallback { .. } => {}
+                ref other => panic!("incorrect result: {other:?}"),
+            },
+            ref other => panic!("incorrect result: {other:?}"),
+        },
+        other => panic!("incorrect result: {other:?}"),
+    };
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_function() -> Result<()> {
+    let lua = Lua::new();
+
+    let f = lua
+        .create_function(|_, ()| Ok("hello, world!"))?
+        .into_owned();
+    drop(lua);
+
+    // We still should be able to call the function despite Lua is dropped
+    let s = f.call::<_, String>(())?;
+    assert_eq!(s.to_string_lossy(), "hello, world!");
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_function_drop() -> Result<()> {
+    let rc = std::sync::Arc::new(());
+
+    {
+        let lua = Lua::new();
+
+        lua.set_app_data(rc.clone());
+
+        let f1 = lua
+            .create_function(|_, ()| Ok("hello, world!"))?
+            .into_owned();
+        let f2 =
+            lua.create_function(move |_, ()| f1.to_ref().call::<_, std::string::String>(()))?;
+        assert_eq!(f2.call::<_, String>(())?.to_string_lossy(), "hello, world!");
+    }
+
+    // Check that Lua is properly destroyed
+    // It works because we collect garbage when Lua goes out of scope
+    assert_eq!(std::sync::Arc::strong_count(&rc), 1);
+
+    Ok(())
+}

tests/hooks.rs

@@ -9,11 +9,9 @@ use std::sync::{Arc, Mutex};
 use mlua::{DebugEvent, Error, HookTriggers, Lua, Result, Value};
 
 #[test]
-fn test_hook_triggers_bitor() {
-    let trigger = HookTriggers::on_calls()
-        | HookTriggers::on_returns()
-        | HookTriggers::every_line()
-        | HookTriggers::every_nth_instruction(5);
+fn test_hook_triggers() {
+    let trigger = HookTriggers::new().on_calls().on_returns()
+        | HookTriggers::new().every_line().every_nth_instruction(5);
 
     assert!(trigger.on_calls);
     assert!(trigger.on_returns);
@@ -27,7 +25,7 @@ fn test_line_counts() -> Result<()> {
     let hook_output = output.clone();
 
     let lua = Lua::new();
-    lua.set_hook(HookTriggers::every_line(), move |_lua, debug| {
+    lua.set_hook(HookTriggers::EVERY_LINE, move |_lua, debug| {
         assert_eq!(debug.event(), DebugEvent::Line);
         hook_output.lock().unwrap().push(debug.curr_line());
         Ok(())
@@ -59,7 +57,7 @@ fn test_function_calls() -> Result<()> {
     let hook_output = output.clone();
 
     let lua = Lua::new();
-    lua.set_hook(HookTriggers::on_calls(), move |_lua, debug| {
+    lua.set_hook(HookTriggers::ON_CALLS, move |_lua, debug| {
         assert_eq!(debug.event(), DebugEvent::Call);
         let names = debug.names();
         let source = debug.source();
@@ -104,7 +102,7 @@ fn test_function_calls() -> Result<()> {
 fn test_error_within_hook() -> Result<()> {
     let lua = Lua::new();
 
-    lua.set_hook(HookTriggers::every_line(), |_lua, _debug| {
+    lua.set_hook(HookTriggers::EVERY_LINE, |_lua, _debug| {
         Err(Error::RuntimeError(
             "Something happened in there!".to_string(),
         ))
@@ -136,7 +134,7 @@ fn test_limit_execution_instructions() -> Result<()> {
 
     let max_instructions = AtomicI64::new(10000);
     lua.set_hook(
-        HookTriggers::every_nth_instruction(30),
+        HookTriggers::new().every_nth_instruction(30),
         move |_lua, debug| {
             assert_eq!(debug.event(), DebugEvent::Count);
             if max_instructions.fetch_sub(30, Ordering::Relaxed) <= 30 {
@@ -166,11 +164,14 @@ fn test_limit_execution_instructions() -> Result<()> {
 fn test_hook_removal() -> Result<()> {
     let lua = Lua::new();
 
-    lua.set_hook(HookTriggers::every_nth_instruction(1), |_lua, _debug| {
-        Err(Error::RuntimeError(
-            "this hook should've been removed by this time".to_string(),
-        ))
-    })?;
+    lua.set_hook(
+        HookTriggers::new().every_nth_instruction(1),
+        |_lua, _debug| {
+            Err(Error::RuntimeError(
+                "this hook should've been removed by this time".to_string(),
+            ))
+        },
+    )?;
 
     assert!(lua.load("local x = 1").exec().is_err());
     lua.remove_hook();
@@ -193,11 +194,11 @@ fn test_hook_swap_within_hook() -> Result<()> {
         tl.borrow()
             .as_ref()
             .unwrap()
-            .set_hook(HookTriggers::every_line(), move |lua, _debug| {
+            .set_hook(HookTriggers::EVERY_LINE, move |lua, _debug| {
                 lua.globals().set("ok", 1i64)?;
                 TL_LUA.with(|tl| {
                     tl.borrow().as_ref().unwrap().set_hook(
-                        HookTriggers::every_line(),
+                        HookTriggers::EVERY_LINE,
                         move |lua, _debug| {
                             lua.load(
                                 r#"
@@ -233,3 +234,39 @@ fn test_hook_swap_within_hook() -> Result<()> {
         Ok(())
     })
 }
+
+#[test]
+fn test_hook_threads() -> Result<()> {
+    let lua = Lua::new();
+
+    let func = lua
+        .load(
+            r#"
+            local x = 2 + 3
+            local y = x * 63
+            local z = string.len(x..", "..y)
+        "#,
+        )
+        .into_function()?;
+    let co = lua.create_thread(func)?;
+
+    let output = Arc::new(Mutex::new(Vec::new()));
+    let hook_output = output.clone();
+    co.set_hook(HookTriggers::EVERY_LINE, move |_lua, debug| {
+        assert_eq!(debug.event(), DebugEvent::Line);
+        hook_output.lock().unwrap().push(debug.curr_line());
+        Ok(())
+    });
+
+    co.resume(())?;
+    lua.remove_hook();
+
+    let output = output.lock().unwrap();
+    if cfg!(feature = "luajit") && lua.load("jit.version_num").eval::<i64>()? >= 20100 {
+        assert_eq!(*output, vec![2, 3, 4, 0, 4]);
+    } else {
+        assert_eq!(*output, vec![2, 3, 4]);
+    }
+
+    Ok(())
+}

tests/luau.rs

@@ -9,6 +9,16 @@ use std::sync::Arc;
 
 use mlua::{Compiler, CoverageInfo, Error, Lua, Result, Table, ThreadStatus, Value, VmState};
 
+#[test]
+fn test_version() -> Result<()> {
+    let lua = Lua::new();
+    assert!(lua
+        .globals()
+        .get::<_, String>("_VERSION")?
+        .starts_with("Luau 0."));
+    Ok(())
+}
+
 #[test]
 fn test_require() -> Result<()> {
     let lua = Lua::new();
@@ -173,7 +183,7 @@ fn test_interrupts() -> Result<()> {
     let interrupts_count = Arc::new(AtomicU64::new(0));
     let interrupts_count2 = interrupts_count.clone();
 
-    lua.set_interrupt(move || {
+    lua.set_interrupt(move |_| {
         interrupts_count2.fetch_add(1, Ordering::Relaxed);
         Ok(VmState::Continue)
     });
@@ -195,7 +205,7 @@ fn test_interrupts() -> Result<()> {
     //
     let yield_count = Arc::new(AtomicU64::new(0));
     let yield_count2 = yield_count.clone();
-    lua.set_interrupt(move || {
+    lua.set_interrupt(move |_| {
         if yield_count2.fetch_add(1, Ordering::Relaxed) == 1 {
             return Ok(VmState::Yield);
         }
@@ -222,7 +232,7 @@ fn test_interrupts() -> Result<()> {
     //
     // Test errors in interrupts
     //
-    lua.set_interrupt(|| Err(Error::RuntimeError("error from interrupt".into())));
+    lua.set_interrupt(|_| Err(Error::RuntimeError("error from interrupt".into())));
     match f.call::<_, ()>(()) {
         Err(Error::CallbackError { cause, .. }) => match *cause {
             Error::RuntimeError(ref m) if m == "error from interrupt" => {}

tests/memory.rs

@@ -1,11 +1,7 @@
 use std::sync::Arc;
 
-use mlua::{GCMode, Lua, Result, UserData};
+use mlua::{Error, GCMode, Lua, Result, UserData};
 
-#[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
-use mlua::Error;
-
-#[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
 #[test]
 fn test_memory_limit() -> Result<()> {
     let lua = Lua::new();
@@ -21,6 +17,15 @@ fn test_memory_limit() -> Result<()> {
         .into_function()?;
     f.call::<_, ()>(()).expect("should trigger no memory limit");
 
+    if cfg!(feature = "luajit") && cfg!(not(feature = "vendored")) {
+        // we don't support setting memory limit for non-vendored luajit
+        assert!(matches!(
+            lua.set_memory_limit(0),
+            Err(Error::MemoryLimitNotAvailable)
+        ));
+        return Ok(());
+    }
+
     lua.set_memory_limit(initial_memory + 10000)?;
     match f.call::<_, ()>(()) {
         Err(Error::MemoryError(_)) => {}
@@ -33,6 +38,29 @@ fn test_memory_limit() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_memory_limit_thread() -> Result<()> {
+    let lua = Lua::new();
+
+    let f = lua
+        .load("local t = {}; for i = 1,10000 do t[i] = i end")
+        .into_function()?;
+
+    if cfg!(feature = "luajit") && cfg!(not(feature = "vendored")) {
+        // we don't support setting memory limit for non-vendored luajit
+        return Ok(());
+    }
+
+    lua.set_memory_limit(lua.used_memory() + 10000)?;
+    let thread = lua.create_thread(f)?;
+    match thread.resume::<_, ()>(()) {
+        Err(Error::MemoryError(_)) => {}
+        something_else => panic!("did not trigger memory error: {:?}", something_else),
+    };
+
+    Ok(())
+}
+
 #[test]
 fn test_gc_control() -> Result<()> {
     let lua = Lua::new();

tests/module/Cargo.toml

@@ -1,8 +1,8 @@
 [package]
-name = "rust_module"
+name = "test_module"
 version = "0.0.0"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
-edition = "2018"
+edition = "2021"
 
 [lib]
 crate-type = ["cdylib"]

tests/module/loader/Cargo.toml

@@ -2,7 +2,7 @@
 name = "module_loader"
 version = "0.0.0"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
-edition = "2018"
+edition = "2021"
 
 [features]
 lua54 = ["mlua/lua54"]

tests/module/loader/tests/load.rs

@@ -8,7 +8,7 @@ fn test_module() -> Result<()> {
     let lua = make_lua()?;
     lua.load(
         r#"
-        local mod = require("rust_module")
+        local mod = require("test_module")
         assert(mod.sum(2,2) == 4)
     "#,
     )
@@ -20,8 +20,8 @@ fn test_module_multi() -> Result<()> {
     let lua = make_lua()?;
     lua.load(
         r#"
-        local mod = require("rust_module")
-        local mod2 = require("rust_module.second")
+        local mod = require("test_module")
+        local mod2 = require("test_module.second")
         assert(mod.check_userdata(mod2.userdata) == 123)
     "#,
     )
@@ -33,7 +33,7 @@ fn test_module_error() -> Result<()> {
     let lua = make_lua()?;
     lua.load(
         r#"
-        local ok, err = pcall(require, "rust_module.error")
+        local ok, err = pcall(require, "test_module.error")
         assert(not ok)
         assert(string.find(tostring(err), "custom module error"))
     "#,
@@ -55,7 +55,7 @@ fn test_module_from_thread() -> Result<()> {
         local mod
 
         local co = coroutine.create(function(a, b)
-            mod = require("rust_module")
+            mod = require("test_module")
             assert(mod.sum(a, b) == a + b)
         end)
 

tests/module/src/lib.rs

@@ -8,12 +8,12 @@ fn used_memory(lua: &Lua, _: ()) -> LuaResult<usize> {
     Ok(lua.used_memory())
 }
 
-fn check_userdata(_: &Lua, ud: MyUserData) -> LuaResult<i32> {
-    Ok(ud.0)
+fn check_userdata(_: &Lua, ud: LuaAnyUserData) -> LuaResult<i32> {
+    Ok(ud.borrow::<MyUserData>()?.0)
 }
 
 #[mlua::lua_module]
-fn rust_module(lua: &Lua) -> LuaResult<LuaTable> {
+fn test_module(lua: &Lua) -> LuaResult<LuaTable> {
     let exports = lua.create_table()?;
     exports.set("sum", lua.create_function(sum)?)?;
     exports.set("used_memory", lua.create_function(used_memory)?)?;
@@ -26,14 +26,14 @@ struct MyUserData(i32);
 
 impl LuaUserData for MyUserData {}
 
-#[mlua::lua_module]
-fn rust_module_second(lua: &Lua) -> LuaResult<LuaTable> {
+#[mlua::lua_module(name = "test_module_second")]
+fn test_module2(lua: &Lua) -> LuaResult<LuaTable> {
     let exports = lua.create_table()?;
-    exports.set("userdata", lua.create_userdata(MyUserData(123))?)?;
+    exports.set("userdata", MyUserData(123))?;
     Ok(exports)
 }
 
 #[mlua::lua_module]
-fn rust_module_error(_: &Lua) -> LuaResult<LuaTable> {
-    Err("custom module error".to_lua_err())
+fn test_module_error(_: &Lua) -> LuaResult<LuaTable> {
+    Err("custom module error".into_lua_err())
 }

tests/scope.rs

@@ -356,3 +356,107 @@ fn test_scope_nonstatic_userdata_drop() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_scope_userdata_ref() -> Result<()> {
+    let lua = Lua::new();
+
+    struct MyUserData(Cell<i64>);
+
+    impl UserData for MyUserData {
+        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+            methods.add_method("inc", |_, data, ()| {
+                data.0.set(data.0.get() + 1);
+                Ok(())
+            });
+
+            methods.add_method("dec", |_, data, ()| {
+                data.0.set(data.0.get() - 1);
+                Ok(())
+            });
+        }
+    }
+
+    let data = MyUserData(Cell::new(1));
+    lua.scope(|scope| {
+        let ud = scope.create_userdata_ref(&data)?;
+        modify_userdata(&lua, ud)
+    })?;
+    assert_eq!(data.0.get(), 2);
+
+    Ok(())
+}
+
+#[test]
+fn test_scope_userdata_ref_mut() -> Result<()> {
+    let lua = Lua::new();
+
+    struct MyUserData(i64);
+
+    impl UserData for MyUserData {
+        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+            methods.add_method_mut("inc", |_, data, ()| {
+                data.0 += 1;
+                Ok(())
+            });
+
+            methods.add_method_mut("dec", |_, data, ()| {
+                data.0 -= 1;
+                Ok(())
+            });
+        }
+    }
+
+    let mut data = MyUserData(1);
+    lua.scope(|scope| {
+        let ud = scope.create_userdata_ref_mut(&mut data)?;
+        modify_userdata(&lua, ud)
+    })?;
+    assert_eq!(data.0, 2);
+
+    Ok(())
+}
+
+#[test]
+fn test_scope_any_userdata_ref() -> Result<()> {
+    let lua = Lua::new();
+
+    lua.register_userdata_type::<Cell<i64>>(|reg| {
+        reg.add_method("inc", |_, data, ()| {
+            data.set(data.get() + 1);
+            Ok(())
+        });
+
+        reg.add_method("dec", |_, data, ()| {
+            data.set(data.get() - 1);
+            Ok(())
+        });
+    })?;
+
+    let data = Cell::new(1i64);
+    lua.scope(|scope| {
+        let ud = scope.create_any_userdata_ref(&data)?;
+        modify_userdata(&lua, ud)
+    })?;
+    assert_eq!(data.get(), 2);
+
+    Ok(())
+}
+
+fn modify_userdata(lua: &Lua, ud: AnyUserData) -> Result<()> {
+    let f: Function = lua
+        .load(
+            r#"
+    function(u)
+        u:inc()
+        u:dec()
+        u:inc()
+    end
+"#,
+        )
+        .eval()?;
+
+    f.call(ud)?;
+
+    Ok(())
+}

tests/serde.rs

@@ -1,6 +1,7 @@
 #![cfg(feature = "serialize")]
 
 use std::collections::HashMap;
+use std::error::Error as StdError;
 
 use mlua::{
     DeserializeOptions, Error, Lua, LuaSerdeExt, Result as LuaResult, SerializeOptions, UserData,
@@ -9,7 +10,7 @@ use mlua::{
 use serde::{Deserialize, Serialize};
 
 #[test]
-fn test_serialize() -> Result<(), Box<dyn std::error::Error>> {
+fn test_serialize() -> Result<(), Box<dyn StdError>> {
     #[derive(Serialize)]
     struct MyUserData(i64, String);
 
@@ -115,7 +116,7 @@ fn test_serialize_in_scope() -> LuaResult<()> {
 }
 
 #[test]
-fn test_serialize_failure() -> Result<(), Box<dyn std::error::Error>> {
+fn test_serialize_failure() -> Result<(), Box<dyn StdError>> {
     #[derive(Serialize)]
     struct MyUserData(i64);
 
@@ -146,7 +147,7 @@ fn test_serialize_failure() -> Result<(), Box<dyn std::error::Error>> {
 
 #[cfg(feature = "luau")]
 #[test]
-fn test_serialize_vector() -> Result<(), Box<dyn std::error::Error>> {
+fn test_serialize_vector() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
 
     let globals = lua.globals();
@@ -235,7 +236,7 @@ fn test_to_value_enum() -> LuaResult<()> {
 }
 
 #[test]
-fn test_to_value_with_options() -> Result<(), Box<dyn std::error::Error>> {
+fn test_to_value_with_options() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
     let globals = lua.globals();
     globals.set("null", lua.null())?;
@@ -305,7 +306,7 @@ fn test_to_value_with_options() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_from_value_nested_tables() -> Result<(), Box<dyn std::error::Error>> {
+fn test_from_value_nested_tables() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
 
     let value = lua
@@ -335,7 +336,7 @@ fn test_from_value_nested_tables() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_from_value_struct() -> Result<(), Box<dyn std::error::Error>> {
+fn test_from_value_struct() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
 
     #[derive(Deserialize, PartialEq, Debug)]
@@ -376,7 +377,7 @@ fn test_from_value_struct() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_from_value_newtype_struct() -> Result<(), Box<dyn std::error::Error>> {
+fn test_from_value_newtype_struct() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
 
     #[derive(Deserialize, PartialEq, Debug)]
@@ -389,7 +390,7 @@ fn test_from_value_newtype_struct() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_from_value_enum() -> Result<(), Box<dyn std::error::Error>> {
+fn test_from_value_enum() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
     lua.globals().set("null", lua.null())?;
 
@@ -433,7 +434,7 @@ fn test_from_value_enum() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_from_value_enum_untagged() -> Result<(), Box<dyn std::error::Error>> {
+fn test_from_value_enum_untagged() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
     lua.globals().set("null", lua.null())?;
 
@@ -473,7 +474,7 @@ fn test_from_value_enum_untagged() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_from_value_with_options() -> Result<(), Box<dyn std::error::Error>> {
+fn test_from_value_with_options() -> Result<(), Box<dyn StdError>> {
     let lua = Lua::new();
 
     // Deny unsupported types by default
@@ -528,3 +529,62 @@ fn test_from_value_with_options() -> Result<(), Box<dyn std::error::Error>> {
 
     Ok(())
 }
+
+#[test]
+fn test_from_value_userdata() -> Result<(), Box<dyn StdError>> {
+    let lua = Lua::new();
+
+    // Tuple struct
+    #[derive(Serialize, Deserialize)]
+    struct MyUserData(i64, String);
+
+    impl UserData for MyUserData {}
+
+    let ud = lua.create_ser_userdata(MyUserData(123, "test userdata".into()))?;
+
+    match lua.from_value::<MyUserData>(Value::UserData(ud)) {
+        Ok(_) => {}
+        Err(err) => panic!("expected no errors, got {err:?}"),
+    };
+
+    // Newtype struct
+    #[derive(Serialize, Deserialize)]
+    struct NewtypeUserdata(String);
+
+    impl UserData for NewtypeUserdata {}
+
+    let ud = lua.create_ser_userdata(NewtypeUserdata("newtype userdata".into()))?;
+
+    match lua.from_value::<NewtypeUserdata>(Value::UserData(ud)) {
+        Ok(_) => {}
+        Err(err) => panic!("expected no errors, got {err:?}"),
+    };
+
+    // Option
+    #[derive(Serialize, Deserialize)]
+    struct UnitUserdata;
+
+    impl UserData for UnitUserdata {}
+
+    let ud = lua.create_ser_userdata(UnitUserdata)?;
+
+    match lua.from_value::<Option<()>>(Value::UserData(ud)) {
+        Ok(Some(_)) => {}
+        Ok(_) => panic!("expected `Some`, got `None`"),
+        Err(err) => panic!("expected no errors, got {err:?}"),
+    };
+
+    // Destructed userdata with skip option
+    let ud = lua.create_ser_userdata(NewtypeUserdata("newtype userdata".into()))?;
+    let _ = ud.take::<NewtypeUserdata>()?;
+
+    match lua.from_value_with::<()>(
+        Value::UserData(ud),
+        DeserializeOptions::new().deny_unsupported_types(false),
+    ) {
+        Ok(_) => {}
+        Err(err) => panic!("expected no errors, got {err:?}"),
+    };
+
+    Ok(())
+}

tests/string.rs

@@ -83,3 +83,37 @@ fn test_string_hash() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_string_debug() -> Result<()> {
+    let lua = Lua::new();
+
+    // Valid utf8
+    let s = lua.create_string("hello")?;
+    assert_eq!(format!("{s:?}"), r#""hello""#);
+
+    // Invalid utf8
+    let s = lua.create_string(b"hello\0world\r\n\t\xF0\x90\x80")?;
+    assert_eq!(format!("{s:?}"), r#"b"hello\0world\r\n\t\xf0\x90\x80""#);
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_string() -> Result<()> {
+    let lua = Lua::new();
+
+    let s = lua.create_string("hello, world!")?.into_owned();
+    drop(lua);
+
+    // Shortcuts
+    assert_eq!(s.as_bytes(), b"hello, world!");
+    assert_eq!(s.to_str()?, "hello, world!");
+    assert_eq!(format!("{s:?}"), "\"hello, world!\"");
+
+    // Access via reference
+    assert_eq!(s.to_ref().to_string_lossy(), "hello, world!");
+
+    Ok(())
+}

tests/table.rs

@@ -152,6 +152,53 @@ fn test_table_push_pop() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_table_clear() -> Result<()> {
+    let lua = Lua::new();
+
+    // Check readonly error
+    #[cfg(feature = "luau")]
+    {
+        let t = lua.create_table()?;
+        t.set_readonly(true);
+        assert!(matches!(
+            t.clear(),
+            Err(Error::RuntimeError(err)) if err.contains("attempt to modify a readonly table")
+        ));
+    }
+
+    let t = lua.create_table()?;
+    // Set array and hash parts
+    t.push("abc")?;
+    t.push("bcd")?;
+    t.set("a", "1")?;
+    t.set("b", "2")?;
+    t.clear()?;
+    assert_eq!(t.len()?, 0);
+    assert_eq!(t.pairs::<Value, Value>().count(), 0);
+
+    // Test table with metamethods
+    let t2 = lua
+        .load(
+            r#"
+        setmetatable({1, 2, 3, a = "1"}, {
+            __index = function() error("index error") end,
+            __newindex = function() error("newindex error") end,
+            __len = function() error("len error") end,
+            __pairs = function() error("pairs error") end,
+        })
+    "#,
+        )
+        .eval::<Table>()?;
+    assert_eq!(t2.raw_len(), 3);
+    t2.clear()?;
+    assert_eq!(t2.raw_len(), 0);
+    assert_eq!(t2.raw_get::<_, Value>("a")?, Value::Nil);
+    assert_ne!(t2.get_metatable(), None);
+
+    Ok(())
+}
+
 #[test]
 fn test_table_sequence_from() -> Result<()> {
     let lua = Lua::new();
@@ -345,3 +392,17 @@ fn test_table_call() -> Result<()> {
 
     Ok(())
 }
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_table() -> Result<()> {
+    let lua = Lua::new();
+
+    let table = lua.create_table()?.into_owned();
+    drop(lua);
+
+    table.to_ref().set("abc", 123)?;
+    assert_eq!(table.to_ref().get::<_, i64>("abc")?, 123);
+
+    Ok(())
+}

tests/tests.rs

@@ -69,7 +69,7 @@ fn test_safety() -> Result<()> {
 fn test_load() -> Result<()> {
     let lua = Lua::new();
 
-    let func = lua.load("\treturn 1+2").into_function()?;
+    let func = lua.load("return 1+2").into_function()?;
     let result: i32 = func.call(())?;
     assert_eq!(result, 3);
 
@@ -308,7 +308,7 @@ fn test_error() -> Result<()> {
     .exec()?;
 
     let rust_error_function =
-        lua.create_function(|_, ()| -> Result<()> { Err(TestError.to_lua_err()) })?;
+        lua.create_function(|_, ()| -> Result<()> { Err(TestError.into_lua_err()) })?;
     globals.set("rust_error_function", rust_error_function)?;
 
     let no_error = globals.get::<_, Function>("no_error")?;
@@ -506,7 +506,7 @@ fn test_result_conversions() -> Result<()> {
 
     let err = lua.create_function(|_, ()| {
         Ok(Err::<String, _>(
-            "only through failure can we succeed".to_lua_err(),
+            "only through failure can we succeed".into_lua_err(),
         ))
     })?;
     let ok = lua.create_function(|_, ()| Ok(Ok::<_, Error>("!".to_owned())))?;
@@ -730,9 +730,9 @@ fn test_set_metatable_nil() -> Result<()> {
 fn test_named_registry_value() -> Result<()> {
     let lua = Lua::new();
 
-    lua.set_named_registry_value::<_, i32>("test", 42)?;
+    lua.set_named_registry_value::<i32>("test", 42)?;
     let f = lua.create_function(move |lua, ()| {
-        assert_eq!(lua.named_registry_value::<_, i32>("test")?, 42);
+        assert_eq!(lua.named_registry_value::<i32>("test")?, 42);
         Ok(())
     })?;
 
@@ -887,19 +887,47 @@ fn test_application_data() -> Result<()> {
     lua.set_app_data("test1");
     lua.set_app_data(vec!["test2"]);
 
+    // Borrow &str immutably and Vec<&str> mutably
+    let s = lua.app_data_ref::<&str>().unwrap();
+    let mut v = lua.app_data_mut::<Vec<&str>>().unwrap();
+    v.push("test3");
+
+    // Insert of new data or removal should fail now
+    assert!(lua.try_set_app_data::<i32>(123).is_err());
+    match catch_unwind(AssertUnwindSafe(|| lua.set_app_data::<i32>(123))) {
+        Ok(_) => panic!("expected panic"),
+        Err(_) => {}
+    }
+    match catch_unwind(AssertUnwindSafe(|| lua.remove_app_data::<i32>())) {
+        Ok(_) => panic!("expected panic"),
+        Err(_) => {}
+    }
+
+    // Check display and debug impls
+    assert_eq!(format!("{s}"), "test1");
+    assert_eq!(format!("{s:?}"), "\"test1\"");
+
+    // Borrowing immutably and mutably of the same type is not allowed
+    match catch_unwind(AssertUnwindSafe(|| lua.app_data_mut::<&str>().unwrap())) {
+        Ok(_) => panic!("expected panic"),
+        Err(_) => {}
+    }
+    drop((s, v));
+
+    // Test that application data is accessible from anywhere
     let f = lua.create_function(|lua, ()| {
-        {
-            let data1 = lua.app_data_ref::<&str>().unwrap();
-            assert_eq!(*data1, "test1");
-        }
-        let mut data2 = lua.app_data_mut::<Vec<&str>>().unwrap();
-        assert_eq!(*data2, vec!["test2"]);
-        data2.push("test3");
+        let mut data1 = lua.app_data_mut::<&str>().unwrap();
+        assert_eq!(*data1, "test1");
+        *data1 = "test4";
+
+        let data2 = lua.app_data_ref::<Vec<&str>>().unwrap();
+        assert_eq!(*data2, vec!["test2", "test3"]);
+
         Ok(())
     })?;
     f.call(())?;
 
-    assert_eq!(*lua.app_data_ref::<&str>().unwrap(), "test1");
+    assert_eq!(*lua.app_data_ref::<&str>().unwrap(), "test4");
     assert_eq!(
         *lua.app_data_ref::<Vec<&str>>().unwrap(),
         vec!["test2", "test3"]
@@ -1072,7 +1100,7 @@ fn test_chunk_env() -> Result<()> {
         test_var = 1
     "#,
     )
-    .set_environment(env1.clone())?
+    .set_environment(env1.clone())
     .exec()?;
 
     lua.load(
@@ -1081,18 +1109,11 @@ fn test_chunk_env() -> Result<()> {
         test_var = 2
     "#,
     )
-    .set_environment(env2.clone())?
+    .set_environment(env2.clone())
     .exec()?;
 
-    assert_eq!(
-        lua.load("test_var").set_environment(env1)?.eval::<i32>()?,
-        1
-    );
-
-    assert_eq!(
-        lua.load("test_var").set_environment(env2)?.eval::<i32>()?,
-        2
-    );
+    assert_eq!(lua.load("test_var").set_environment(env1).eval::<i32>()?, 1);
+    assert_eq!(lua.load("test_var").set_environment(env2).eval::<i32>()?, 2);
 
     Ok(())
 }
@@ -1227,7 +1248,7 @@ fn test_inspect_stack() -> Result<()> {
         assert(logline("world") == '[string "chunk"]:12 world')
     "#,
     )
-    .set_name("chunk")?
+    .set_name("chunk")
     .exec()?;
 
     Ok(())

tests/userdata.rs

@@ -1,3 +1,5 @@
+use std::collections::HashMap;
+use std::string::String as StdString;
 use std::sync::Arc;
 #[cfg(not(feature = "parking_lot"))]
 use std::sync::{Mutex, RwLock};
@@ -12,12 +14,12 @@ use std::{cell::RefCell, rc::Rc};
 use std::sync::atomic::{AtomicI64, Ordering};
 
 use mlua::{
-    AnyUserData, Error, ExternalError, Function, Lua, MetaMethod, Nil, Result, String, UserData,
-    UserDataFields, UserDataMethods, Value,
+    AnyUserData, AnyUserDataExt, Error, ExternalError, Function, Lua, MetaMethod, Nil, Result,
+    String, UserData, UserDataFields, UserDataMethods, UserDataRef, Value,
 };
 
 #[test]
-fn test_user_data() -> Result<()> {
+fn test_userdata() -> Result<()> {
     struct UserData1(i64);
     struct UserData2(Box<i64>);
 
@@ -100,20 +102,25 @@ fn test_metamethods() -> Result<()> {
             methods.add_method("get", |_, data, ()| Ok(data.0));
             methods.add_meta_function(
                 MetaMethod::Add,
-                |_, (lhs, rhs): (MyUserData, MyUserData)| Ok(MyUserData(lhs.0 + rhs.0)),
+                |_, (lhs, rhs): (UserDataRef<Self>, UserDataRef<Self>)| {
+                    Ok(MyUserData(lhs.0 + rhs.0))
+                },
             );
             methods.add_meta_function(
                 MetaMethod::Sub,
-                |_, (lhs, rhs): (MyUserData, MyUserData)| Ok(MyUserData(lhs.0 - rhs.0)),
+                |_, (lhs, rhs): (UserDataRef<Self>, UserDataRef<Self>)| {
+                    Ok(MyUserData(lhs.0 - rhs.0))
+                },
+            );
+            methods.add_meta_function(
+                MetaMethod::Eq,
+                |_, (lhs, rhs): (UserDataRef<Self>, UserDataRef<Self>)| Ok(lhs.0 == rhs.0),
             );
-            methods.add_meta_function(MetaMethod::Eq, |_, (lhs, rhs): (MyUserData, MyUserData)| {
-                Ok(lhs.0 == rhs.0)
-            });
             methods.add_meta_method(MetaMethod::Index, |_, data, index: String| {
                 if index.to_str()? == "inner" {
                     Ok(data.0)
                 } else {
-                    Err("no such custom index".to_lua_err())
+                    Err("no such custom index".into_lua_err())
                 }
             });
             #[cfg(any(
@@ -124,13 +131,14 @@ fn test_metamethods() -> Result<()> {
             ))]
             methods.add_meta_method(MetaMethod::Pairs, |lua, data, ()| {
                 use std::iter::FromIterator;
-                let stateless_iter = lua.create_function(|_, (data, i): (MyUserData, i64)| {
-                    let i = i + 1;
-                    if i <= data.0 {
-                        return Ok(mlua::Variadic::from_iter(vec![i, i]));
-                    }
-                    return Ok(mlua::Variadic::new());
-                })?;
+                let stateless_iter =
+                    lua.create_function(|_, (data, i): (UserDataRef<Self>, i64)| {
+                        let i = i + 1;
+                        if i <= data.0 {
+                            return Ok(mlua::Variadic::from_iter(vec![i, i]));
+                        }
+                        return Ok(mlua::Variadic::new());
+                    })?;
                 Ok((stateless_iter, data.clone(), 0))
             });
         }
@@ -142,7 +150,9 @@ fn test_metamethods() -> Result<()> {
     globals.set("userdata2", MyUserData(3))?;
     globals.set("userdata3", MyUserData(3))?;
     assert_eq!(
-        lua.load("userdata1 + userdata2").eval::<MyUserData>()?.0,
+        lua.load("userdata1 + userdata2")
+            .eval::<UserDataRef<MyUserData>>()?
+            .0,
         10
     );
 
@@ -166,7 +176,12 @@ fn test_metamethods() -> Result<()> {
         )
         .eval::<Function>()?;
 
-    assert_eq!(lua.load("userdata1 - userdata2").eval::<MyUserData>()?.0, 4);
+    assert_eq!(
+        lua.load("userdata1 - userdata2")
+            .eval::<UserDataRef<MyUserData>>()?
+            .0,
+        4
+    );
     assert_eq!(lua.load("userdata1:get()").eval::<i64>()?, 7);
     assert_eq!(lua.load("userdata2.inner").eval::<i64>()?, 3);
     assert!(lua.load("userdata2.nonexist_field").eval::<()>().is_err());
@@ -305,21 +320,19 @@ fn test_userdata_take() -> Result<()> {
     fn check_userdata_take(lua: &Lua, userdata: AnyUserData, rc: Arc<i64>) -> Result<()> {
         lua.globals().set("userdata", userdata.clone())?;
         assert_eq!(Arc::strong_count(&rc), 3);
-        let userdata_copy = userdata.clone();
         {
             let _value = userdata.borrow::<MyUserdata>()?;
             // We should not be able to take userdata if it's borrowed
-            match userdata_copy.take::<MyUserdata>() {
+            match userdata.take::<MyUserdata>() {
                 Err(Error::UserDataBorrowMutError) => {}
                 r => panic!("expected `UserDataBorrowMutError` error, got {:?}", r),
             }
         }
 
-        let value = userdata_copy.take::<MyUserdata>()?;
+        let value = userdata.take::<MyUserdata>()?;
         assert_eq!(*value.0, 18);
         drop(value);
-        lua.gc_collect()?;
-        assert_eq!(Arc::strong_count(&rc), 1);
+        assert_eq!(Arc::strong_count(&rc), 2);
 
         match userdata.borrow::<MyUserdata>() {
             Err(Error::UserDataDestructed) => {}
@@ -332,6 +345,13 @@ fn test_userdata_take() -> Result<()> {
             },
             r => panic!("improper return for destructed userdata: {:?}", r),
         }
+
+        drop(userdata);
+        lua.globals().raw_remove("userdata")?;
+        lua.gc_collect()?;
+        lua.gc_collect()?;
+        assert_eq!(Arc::strong_count(&rc), 1);
+
         Ok(())
     }
 
@@ -403,9 +423,9 @@ fn test_user_values() -> Result<()> {
     ud.set_named_user_value("name", "alex")?;
     ud.set_named_user_value("age", 10)?;
 
-    assert_eq!(ud.get_named_user_value::<_, String>("name")?, "alex");
-    assert_eq!(ud.get_named_user_value::<_, i32>("age")?, 10);
-    assert_eq!(ud.get_named_user_value::<_, Value>("nonexist")?, Value::Nil);
+    assert_eq!(ud.get_named_user_value::<String>("name")?, "alex");
+    assert_eq!(ud.get_named_user_value::<i32>("age")?, 10);
+    assert_eq!(ud.get_named_user_value::<Value>("nonexist")?, Value::Nil);
 
     Ok(())
 }
@@ -467,6 +487,7 @@ fn test_fields() -> Result<()> {
 
     impl UserData for MyUserData {
         fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
+            fields.add_field("static", "constant");
             fields.add_field_method_get("val", |_, data| Ok(data.0));
             fields.add_field_method_set("val", |_, data, val| {
                 data.0 = val;
@@ -478,11 +499,7 @@ fn test_fields() -> Result<()> {
             fields
                 .add_field_function_set("uval", |_, ud, s| ud.set_user_value::<Option<String>>(s));
 
-            fields.add_meta_field_with(MetaMethod::Index, |lua| {
-                let index = lua.create_table()?;
-                index.set("f", 321)?;
-                Ok(index)
-            });
+            fields.add_meta_field(MetaMethod::Index, HashMap::from([("f", 321)]));
             fields.add_meta_field_with(MetaMethod::NewIndex, |lua| {
                 lua.create_function(|lua, (_, field, val): (AnyUserData, String, Value)| {
                     lua.globals().set(field, val)?;
@@ -497,6 +514,7 @@ fn test_fields() -> Result<()> {
     globals.set("ud", MyUserData(7))?;
     lua.load(
         r#"
+        assert(ud.static == "constant")
         assert(ud.val == 7)
         ud.val = 10
         assert(ud.val == 10)
@@ -519,35 +537,27 @@ fn test_fields() -> Result<()> {
 #[test]
 fn test_metatable() -> Result<()> {
     #[derive(Copy, Clone)]
-    struct MyUserData(i64);
+    struct MyUserData;
 
     impl UserData for MyUserData {
-        fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
-            fields.add_meta_field_with("__type_name", |_| Ok("MyUserData"));
-        }
-
         fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
             methods.add_function("my_type_name", |_, data: AnyUserData| {
                 let metatable = data.get_metatable()?;
-                metatable.get::<_, String>("__type_name")
+                metatable.get::<String>("__name")
             });
         }
     }
 
     let lua = Lua::new();
     let globals = lua.globals();
-    globals.set("ud", MyUserData(7))?;
-    lua.load(
-        r#"
-        assert(ud:my_type_name() == "MyUserData")
-    "#,
-    )
-    .exec()?;
+    globals.set("ud", MyUserData)?;
+    lua.load(r#"assert(ud:my_type_name() == "MyUserData")"#)
+        .exec()?;
 
     let ud: AnyUserData = globals.get("ud")?;
     let metatable = ud.get_metatable()?;
 
-    match metatable.get::<_, Value>("__gc") {
+    match metatable.get::<Value>("__gc") {
         Ok(_) => panic!("expected MetaMethodRestricted, got no error"),
         Err(Error::MetaMethodRestricted(_)) => {}
         Err(e) => panic!("expected MetaMethodRestricted, got {:?}", e),
@@ -561,14 +571,13 @@ fn test_metatable() -> Result<()> {
 
     let mut methods = metatable
         .pairs()
-        .into_iter()
         .map(|kv: Result<(_, Value)>| Ok(kv?.0))
         .collect::<Result<Vec<_>>>()?;
-    methods.sort_by_cached_key(|k| k.name().to_owned());
-    assert_eq!(methods, vec![MetaMethod::Index, "__type_name".into()]);
+    methods.sort();
+    assert_eq!(methods, vec!["__index", "__name"]);
 
     #[derive(Copy, Clone)]
-    struct MyUserData2(i64);
+    struct MyUserData2;
 
     impl UserData for MyUserData2 {
         fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
@@ -576,12 +585,25 @@ fn test_metatable() -> Result<()> {
         }
     }
 
-    match lua.create_userdata(MyUserData2(1)) {
+    match lua.create_userdata(MyUserData2) {
         Ok(_) => panic!("expected MetaMethodTypeError, got no error"),
         Err(Error::MetaMethodTypeError { .. }) => {}
         Err(e) => panic!("expected MetaMethodTypeError, got {:?}", e),
     }
 
+    #[derive(Copy, Clone)]
+    struct MyUserData3;
+
+    impl UserData for MyUserData3 {
+        fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
+            fields.add_meta_field_with("__name", |_| Ok("CustomName"));
+        }
+    }
+
+    let ud = lua.create_userdata(MyUserData3)?;
+    let metatable = ud.get_metatable()?;
+    assert_eq!(metatable.get::<String>("__name")?.to_str()?, "CustomName");
+
     Ok(())
 }
 
@@ -591,6 +613,7 @@ fn test_userdata_wrapped() -> Result<()> {
 
     impl UserData for MyUserData {
         fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
+            fields.add_field("static", "constant");
             fields.add_field_method_get("data", |_, this| Ok(this.0));
             fields.add_field_method_set("data", |_, this, val| {
                 this.0 = val;
@@ -608,6 +631,7 @@ fn test_userdata_wrapped() -> Result<()> {
         globals.set("rc_refcell_ud", ud1.clone())?;
         lua.load(
             r#"
+            assert(rc_refcell_ud.static == "constant")
             rc_refcell_ud.data = rc_refcell_ud.data + 1
             assert(rc_refcell_ud.data == 2)
         "#,
@@ -623,6 +647,7 @@ fn test_userdata_wrapped() -> Result<()> {
     globals.set("arc_mutex_ud", ud2.clone())?;
     lua.load(
         r#"
+        assert(arc_mutex_ud.static == "constant")
         arc_mutex_ud.data = arc_mutex_ud.data + 1
         assert(arc_mutex_ud.data == 3)
     "#,
@@ -637,6 +662,7 @@ fn test_userdata_wrapped() -> Result<()> {
     globals.set("arc_rwlock_ud", ud3.clone())?;
     lua.load(
         r#"
+        assert(arc_rwlock_ud.static == "constant")
         arc_rwlock_ud.data = arc_rwlock_ud.data + 1
         assert(arc_rwlock_ud.data == 4)
     "#,
@@ -663,7 +689,7 @@ fn test_userdata_proxy() -> Result<()> {
 
     impl UserData for MyUserData {
         fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
-            fields.add_field_function_get("static_field", |_, _| Ok(123));
+            fields.add_field("static_field", 123);
             fields.add_field_method_get("n", |_, this| Ok(this.0));
         }
 
@@ -697,3 +723,124 @@ fn test_userdata_proxy() -> Result<()> {
     )
     .exec()
 }
+
+#[test]
+fn test_any_userdata() -> Result<()> {
+    let lua = Lua::new();
+
+    lua.register_userdata_type::<StdString>(|reg| {
+        reg.add_method("get", |_, this, ()| Ok(this.clone()));
+        reg.add_method_mut("concat", |_, this, s: String| {
+            this.push_str(&s.to_string_lossy());
+            Ok(())
+        });
+    })?;
+
+    let ud = lua.create_any_userdata("hello".to_string())?;
+    assert_eq!(&*ud.borrow::<StdString>()?, "hello");
+
+    lua.globals().set("ud", ud)?;
+    lua.load(
+        r#"
+        assert(ud:get() == "hello")
+        ud:concat(", world")
+        assert(ud:get() == "hello, world")
+    "#,
+    )
+    .exec()
+    .unwrap();
+
+    Ok(())
+}
+
+#[test]
+fn test_userdata_ext() -> Result<()> {
+    let lua = Lua::new();
+
+    #[derive(Clone, Copy)]
+    struct MyUserData(u32);
+
+    impl UserData for MyUserData {
+        fn add_fields<'lua, F: UserDataFields<'lua, Self>>(fields: &mut F) {
+            fields.add_field_method_get("n", |_, this| Ok(this.0));
+            fields.add_field_method_set("n", |_, this, val| {
+                this.0 = val;
+                Ok(())
+            });
+        }
+
+        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+            methods.add_meta_method(MetaMethod::Call, |_, _this, ()| Ok("called"));
+            methods.add_method_mut("add", |_, this, x: u32| {
+                this.0 += x;
+                Ok(())
+            });
+        }
+    }
+
+    let ud = lua.create_userdata(MyUserData(123))?;
+
+    assert_eq!(ud.get::<_, u32>("n")?, 123);
+    ud.set("n", 321)?;
+    assert_eq!(ud.get::<_, u32>("n")?, 321);
+    assert_eq!(ud.get::<_, Option<u32>>("non-existent")?, None);
+    match ud.set::<_, u32>("non-existent", 123) {
+        Err(Error::RuntimeError(_)) => {}
+        r => panic!("expected RuntimeError, got {r:?}"),
+    }
+
+    assert_eq!(ud.call::<_, String>(())?, "called");
+
+    ud.call_method("add", 2)?;
+    assert_eq!(ud.get::<_, u32>("n")?, 323);
+
+    Ok(())
+}
+
+#[test]
+fn test_userdata_method_errors() -> Result<()> {
+    struct MyUserData(i64);
+
+    impl UserData for MyUserData {
+        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+            methods.add_method("get_value", |_, data, ()| Ok(data.0));
+        }
+    }
+
+    let lua = Lua::new();
+
+    let ud = lua.create_userdata(MyUserData(123))?;
+    let res = ud.call_function::<_, ()>("get_value", ());
+    let Err(Error::CallbackError { cause, .. }) = res else {
+        panic!("expected CallbackError, got {res:?}");
+    };
+    assert!(matches!(
+        &*cause,
+        Error::BadArgument {
+            to,
+            name,
+            ..
+        } if to.as_deref() == Some("MyUserData.get_value") && name.as_deref() == Some("self")
+    ));
+
+    Ok(())
+}
+
+#[cfg(all(feature = "unstable", not(feature = "send")))]
+#[test]
+fn test_owned_userdata() -> Result<()> {
+    let lua = Lua::new();
+
+    let ud = lua.create_any_userdata("abc")?.into_owned();
+    drop(lua);
+
+    assert_eq!(*ud.borrow::<&str>()?, "abc");
+    *ud.borrow_mut()? = "cba";
+    assert!(matches!(
+        ud.borrow::<i64>(),
+        Err(Error::UserDataTypeMismatch)
+    ));
+    assert_eq!(ud.take::<&str>()?, "cba");
+
+    Ok(())
+}