v0.5.0

Fix f32-to-f64 conversion tests

.github/workflows/main.yml

@@ -27,7 +27,7 @@ jobs:
     - name: Build ${{ matrix.lua }} vendored
       run: |
         cargo build --release --features "${{ matrix.lua }} vendored"
-        cargo build --release --features "${{ matrix.lua }} vendored async send"
+        cargo build --release --features "${{ matrix.lua }} vendored async send serialize"
       shell: bash
     - name: Build ${{ matrix.lua }} pkg-config
       if: ${{ matrix.os == 'ubuntu-18.04' && matrix.lua != 'lua54' }}
@@ -63,13 +63,13 @@ jobs:
       if: ${{ matrix.os != 'macos-latest' || matrix.lua != 'luajit' }}
       run: |
         cargo test --release --features "${{ matrix.lua }} vendored"
-        cargo test --release --features "${{ matrix.lua }} vendored async send"
+        cargo test --release --features "${{ matrix.lua }} vendored async send serialize"
       shell: bash
-    - name: Run compile tests
-      if: ${{ matrix.os == 'ubuntu-18.04' && matrix.lua == 'lua53' }}
+    - name: Run compile tests (macos lua53)
+      if: ${{ matrix.os == 'macos-latest' && matrix.lua == 'lua53' }}
       run: |
-        cargo test --release --features "${{ matrix.lua }} vendored" -- --ignored
-        cargo test --release --features "${{ matrix.lua }} vendored async send" -- --ignored
+        TRYBUILD=overwrite cargo test --release --features "${{ matrix.lua }} vendored" -- --ignored
+        TRYBUILD=overwrite cargo test --release --features "${{ matrix.lua }} vendored async send serialize" -- --ignored
       shell: bash
 
   test_luajit_macos:
@@ -85,12 +85,12 @@ jobs:
         override: true
     - name: Run LuaJIT 2.0.5 tests
       run: |
-        brew install luajit pkg-config
-        cargo test --tests --release --features "luajit async send" -- --test-threads=1
+        brew install luajit
+        cargo test --tests --release --features "luajit async send serialize" -- --test-threads=1
       shell: bash
     - name: Run LuaJIT vendored tests
       run: |
-        cargo test --release --features "luajit vendored async send"
+        cargo test --release --features "luajit vendored async send serialize"
       shell: bash
 
   test_modules:
@@ -126,21 +126,16 @@ jobs:
     needs: build
     strategy:
       matrix:
-        lua: [lua53, lua51, luajit]
+        lua: [lua53, luajit]
     defaults:
       run:
-        shell: bash.exe --login -eo pipefail "{0}"
-    env:
-      MSYSTEM: MINGW64
-      CHERE_INVOKING: 1
+        shell: msys2 {0}
     steps:
+    - uses: msys2/setup-msys2@v2
     - uses: actions/checkout@v2
-    - name: Set up shell
-      run: echo ::add-path::C:\msys64\usr\bin\
-      shell: pwsh
     - name: Install Rust & Lua
       run: |
-        pacman -S --noconfirm mingw-w64-x86_64-rust mingw-w64-x86_64-lua mingw-w64-x86_64-lua51 mingw-w64-x86_64-luajit
+        pacman -S --noconfirm mingw-w64-x86_64-rust mingw-w64-x86_64-lua mingw-w64-x86_64-luajit mingw-w64-x86_64-pkg-config
     - name: Run ${{ matrix.lua }} module tests
       run: |
         (cd examples/module && cargo build --release --features "${{ matrix.lua }}")
@@ -174,4 +169,4 @@ jobs:
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          args: --features "${{ matrix.lua }},async,send,vendored
+          args: --features "${{ matrix.lua }},vendored,async,send,serialize

CHANGELOG.md

@@ -1,3 +1,14 @@
+## v0.5.0
+
+- Serde support under `serialize` feature flag.
+- Re-export `mlua_derive`.
+
+## v0.4.2
+
+- Added `Function::dump()` to dump lua function to a binary chunk
+- Added `ChunkMode` enum to mark chunks as text or binary
+- Updated `set_memory_limit` doc
+
 ## v0.4.0
 
 - Lua 5.4 support with `MetaMethod::Close`.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua"
-version = "0.4.0"
+version = "0.5.0" # remember to update html_root_url and mlua_derive
 authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@chucklefish.org>"]
 edition = "2018"
 repository = "https://github.com/khvzak/mlua"
@@ -12,16 +12,13 @@ license = "MIT"
 links = "lua"
 build = "build/main.rs"
 description = """
-High level bindings to Lua 5.1/5.2/5.3/5.4 (including LuaJIT)
+High level bindings to Lua 5.4/5.3/5.2/5.1 (including LuaJIT)
 with async/await features and support of writing native lua modules in Rust.
 """
 
-[badges]
-# github-actions = { repository = "khvzak/mlua", workflow = "CI" }
-maintenance = { status = "actively-developed" }
-
 [package.metadata.docs.rs]
-features = ["async"]
+features = ["lua53", "async", "send", "serialize"]
+rustdoc-args = ["--cfg", "docsrs"]
 
 [workspace]
 members = [
@@ -37,32 +34,38 @@ lua52 = []
 lua51 = []
 luajit = []
 vendored = ["lua-src", "luajit-src"]
-module = []
+module = ["mlua_derive"]
 async = ["futures-core", "futures-task", "futures-util"]
 send = []
+serialize = ["serde", "erased-serde"]
 
 [dependencies]
+mlua_derive = { version = "0.5", optional = true, path = "mlua_derive" }
 bstr = { version = "0.2", features = ["std"], default_features = false }
 lazy_static = { version = "1.4" }
-num-traits = { version = "0.2.11" }
+num-traits = { version = "0.2.14" }
 futures-core = { version = "0.3.5", optional = true }
 futures-task = { version = "0.3.5", optional = true }
 futures-util = { version = "0.3.5", optional = true }
+serde = { version = "1.0", optional = true }
+erased-serde = { version = "0.3", optional = true }
 
 [build-dependencies]
 cc = { version = "1.0" }
 pkg-config = { version = "0.3.17" }
-lua-src = { version = "535.0.4", optional = true }
-luajit-src = { version = "210.1.0", optional = true }
+lua-src = { version = ">= 540.0.0, < 550.0.0", optional = true }
+luajit-src = { version = ">= 210.1.0, < 220.0.0", optional = true }
 
 [dev-dependencies]
-rustyline = "6.0"
+rustyline = "7.0"
 criterion = "0.3"
 trybuild = "1.0"
 futures = "0.3.5"
 hyper = "0.13"
+reqwest = { version = "0.10", features = ["json"] }
 tokio = { version = "0.2", features = ["full"] }
 futures-timer = "3.0"
+serde_json = "1.0"
 
 [[bench]]
 name = "benchmark"
@@ -72,6 +75,10 @@ harness = false
 name = "async_http_client"
 required-features = ["async"]
 
+[[example]]
+name = "async_http_reqwest"
+required-features = ["async", "serialize"]
+
 [[example]]
 name = "async_http_server"
 required-features = ["async", "send"]
@@ -79,3 +86,7 @@ required-features = ["async", "send"]
 [[example]]
 name = "async_tcp_server"
 required-features = ["async"]
+
+[[example]]
+name = "serialize"
+required-features = ["serialize"]

README.md

@@ -33,9 +33,20 @@ Starting from v0.3, `mlua` supports async/await for all Lua versions. This works
 
 **Examples**:
 - [HTTP Client](examples/async_http_client.rs)
+- [HTTP Client (json)](examples/async_http_reqwest.rs)
 - [HTTP Server](examples/async_http_server.rs)
 - [TCP Server](examples/async_tcp_server.rs)
 
+### Serialization (serde) support
+
+With `serialize` feature flag enabled, `mlua` allows you to serialize/deserialize any type that implements [`serde::Serialize`] and [`serde::Deserialize`] into/from [`mlua::Value`]. In addition `mlua` provides [`serde::Serialize`] trait implementation for it (including user data support).
+
+[Example](examples/serialize.rs)
+
+[`serde::Serialize`]: https://docs.serde.rs/serde/ser/trait.Serialize.html
+[`serde::Deserialize`]: https://docs.serde.rs/serde/de/trait.Deserialize.html
+[`mlua::Value`]: https://docs.rs/mlua/latest/mlua/enum.Value.html
+
 ### Compiling
 
 You have to enable one of the features `lua54`, `lua53`, `lua52`, `lua51` or `luajit`, according to the choosen Lua version.
@@ -59,7 +70,7 @@ Add to `Cargo.toml` :
 
 ``` toml
 [dependencies]
-mlua = { version = "0.4", features = ["lua53"] }
+mlua = { version = "0.5", features = ["lua53"] }
 ```
 
 `main.rs`
@@ -93,15 +104,12 @@ Add to `Cargo.toml` :
 crate-type = ["cdylib"]
 
 [dependencies]
-mlua = { version = "0.4", features = ["lua53", "module"] }
-mlua_derive = "0.4"
+mlua = { version = "0.5", features = ["lua53", "module"] }
 ```
 
 `lib.rs` :
 
 ``` rust
-#[macro_use]
-extern crate mlua_derive;
 use mlua::prelude::*;
 
 fn hello(_: &Lua, name: String) -> LuaResult<()> {
@@ -109,7 +117,7 @@ fn hello(_: &Lua, name: String) -> LuaResult<()> {
     Ok(())
 }
 
-#[lua_module]
+#[mlua::lua_module]
 fn my_module(lua: &Lua) -> LuaResult<LuaTable> {
     let exports = lua.create_table()?;
     exports.set("hello", lua.create_function(hello)?)?;

benches/benchmark.rs

@@ -5,7 +5,8 @@
 
 #[cfg_attr(
     all(feature = "luajit", target_os = "macos", target_arch = "x86_64"),
-    link_args = "-pagezero_size 10000 -image_base 100000000"
+    link_args = "-pagezero_size 10000 -image_base 100000000",
+    allow(unused_attributes)
 )]
 extern "system" {}
 

examples/async_http_client.rs

@@ -61,7 +61,7 @@ async fn main() -> Result<()> {
     let f = lua
         .load(
             r#"
-            local res = fetch_url(...);
+            local res = fetch_url(...)
             print(res.status)
             for key, vals in pairs(res.headers) do
                 for _, val in ipairs(vals) do

examples/async_http_reqwest.rs

@@ -0,0 +1,41 @@
+use mlua::{Error, Lua, LuaSerdeExt, Result};
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    let lua = Lua::new();
+    let globals = lua.globals();
+    globals.set("null", lua.null()?)?;
+
+    let fetch_json = lua.create_async_function(|lua, uri: String| async move {
+        let resp = reqwest::get(&uri)
+            .await
+            .and_then(|resp| resp.error_for_status())
+            .map_err(Error::external)?;
+        let json = resp
+            .json::<serde_json::Value>()
+            .await
+            .map_err(Error::external)?;
+        lua.to_value(&json)
+    })?;
+    globals.set("fetch_json", fetch_json)?;
+
+    let f = lua
+        .load(
+            r#"
+            function print_r(t, indent)
+                local indent = indent or ''
+                for k, v in pairs(t) do
+                    io.write(indent, tostring(k))
+                    if type(v) == "table" then io.write(':\n') print_r(v, indent..'  ')
+                    else io.write(': ', v == null and "null" or tostring(v), '\n') end
+                end
+            end
+
+            local res = fetch_json(...)
+            print_r(res)
+        "#,
+        )
+        .into_function()?;
+
+    f.call_async("https://httpbin.org/anything?arg0=val0").await
+}

examples/async_tcp_server.rs

@@ -2,8 +2,8 @@ use std::net::Shutdown;
 use std::sync::Arc;
 
 use bstr::BString;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::net::{TcpListener, TcpStream};
-use tokio::prelude::*;
 use tokio::sync::Mutex;
 use tokio::task;
 
@@ -63,7 +63,7 @@ impl UserData for LuaTcpStream {
 
 async fn run_server(lua: &'static Lua) -> Result<()> {
     let spawn = lua.create_function(move |_, func: Function| {
-        task::spawn_local(async move { func.call_async::<_, ()>(()).await.unwrap() });
+        task::spawn_local(async move { func.call_async::<_, ()>(()).await });
         Ok(())
     })?;
 

examples/guided_tour.rs

@@ -164,6 +164,33 @@ fn main() -> Result<()> {
             < f32::EPSILON
     );
 
+    // Normally, Rust types passed to `Lua` must be `'static`, because there is no way to be
+    // sure of their lifetime inside the Lua state. There is, however, a limited way to lift this
+    // requirement. You can call `Lua::scope` to create userdata and callbacks types that only live
+    // for as long as the call to scope, but do not have to be `'static` (and `Send`).
+
+    {
+        let mut rust_val = 0;
+
+        lua.scope(|scope| {
+            // We create a 'sketchy' Lua callback that holds a mutable reference to the variable
+            // `rust_val`.  Outside of a `Lua::scope` call, this would not be allowed
+            // because it could be unsafe.
+
+            lua.globals().set(
+                "sketchy",
+                scope.create_function_mut(|_, ()| {
+                    rust_val = 42;
+                    Ok(())
+                })?,
+            )?;
+
+            lua.load("sketchy()").exec()
+        })?;
+
+        assert_eq!(rust_val, 42);
+    }
+
     // We were able to run our 'sketchy' function inside the scope just fine.  However, if we
     // try to run our 'sketchy' function outside of the scope, the function we created will have
     // been invalidated and we will generate an error.  If our function wasn't invalidated, we

examples/module/Cargo.toml

@@ -17,4 +17,3 @@ vendored = ["mlua/vendored"]
 
 [dependencies]
 mlua = { path = "../..", features = ["module"] }
-mlua_derive = { path = "../../mlua_derive" }

examples/module/src/lib.rs

@@ -8,7 +8,7 @@ fn used_memory(lua: &Lua, _: ()) -> LuaResult<usize> {
     Ok(lua.used_memory())
 }
 
-#[mlua_derive::lua_module]
+#[mlua::lua_module]
 fn rust_module(lua: &Lua) -> LuaResult<LuaTable> {
     let exports = lua.create_table()?;
     exports.set("sum", lua.create_function(sum)?)?;

examples/serialize.rs

@@ -0,0 +1,66 @@
+use mlua::{Error, Lua, LuaSerdeExt, Result, UserData, Value};
+use serde::{Deserialize, Serialize};
+
+#[derive(Serialize, Deserialize)]
+enum Transmission {
+    Manual,
+    Automatic,
+}
+
+#[derive(Serialize, Deserialize)]
+struct Engine {
+    v: u32,
+    kw: u32,
+}
+
+#[derive(Serialize, Deserialize)]
+struct Car {
+    active: bool,
+    model: String,
+    transmission: Transmission,
+    engine: Engine,
+}
+
+impl UserData for Car {}
+
+fn main() -> Result<()> {
+    let lua = Lua::new();
+    let globals = lua.globals();
+
+    // Create Car struct from a Lua table
+    let car: Car = lua.from_value(lua.load(r#"
+        {active = true, model = "Volkswagen Golf", transmission = "Automatic", engine = {v = 1499, kw = 90}}
+    "#).eval()?)?;
+
+    // Set it as (serializable) userdata
+    globals.set("null", lua.null()?)?;
+    globals.set("array_mt", lua.array_metatable()?)?;
+    globals.set("car", lua.create_ser_userdata(car)?)?;
+
+    // Create a Lua table with multiple data types
+    let val: Value = lua
+        .load(r#"{driver = "Boris", car = car, price = null, points = setmetatable({}, array_mt)}"#)
+        .eval()?;
+
+    // Serialize the table above to JSON
+    let json_str = serde_json::to_string(&val).map_err(Error::external)?;
+    println!("{}", json_str);
+
+    // Create Lua Value from JSON (or any serializable type)
+    let json = serde_json::json!({
+        "key": "value",
+        "null": null,
+        "array": [],
+    });
+    globals.set("json_value", lua.to_value(&json)?)?;
+    lua.load(
+        r#"
+        assert(json_value["key"] == "value")
+        assert(json_value["null"] == null)
+        assert(#(json_value["array"]) == 0)
+    "#,
+    )
+    .exec()?;
+
+    Ok(())
+}

mlua_derive/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua_derive"
-version = "0.4.0"
+version = "0.5.0"
 authors = ["Aleksandr Orlenko <zxteam@pm.me>"]
 edition = "2018"
 description = "Procedural macros for the mlua crate."

src/conversion.rs

@@ -1,4 +1,4 @@
-use std::collections::{BTreeMap, HashMap};
+use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::ffi::{CStr, CString};
 use std::hash::{BuildHasher, Hash};
 use std::string::String as StdString;
@@ -481,6 +481,56 @@ 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> {
+    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Table(lua.create_table_from(
+            self.into_iter().map(|val| (val, true)),
+        )?))
+    }
+}
+
+impl<'lua, T: Eq + Hash + FromLua<'lua>, S: BuildHasher + Default> FromLua<'lua> for HashSet<T, S> {
+    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
+        if let Value::Table(table) = value {
+            table
+                .pairs::<T, Value<'lua>>()
+                .map(|res| res.map(|(k, _)| k))
+                .collect()
+        } else {
+            Err(Error::FromLuaConversionError {
+                from: value.type_name(),
+                to: "HashSet",
+                message: Some("expected table".to_string()),
+            })
+        }
+    }
+}
+
+impl<'lua, T: Ord + ToLua<'lua>> ToLua<'lua> for BTreeSet<T> {
+    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Table(lua.create_table_from(
+            self.into_iter().map(|val| (val, true)),
+        )?))
+    }
+}
+
+impl<'lua, T: Ord + FromLua<'lua>> FromLua<'lua> for BTreeSet<T> {
+    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
+        if let Value::Table(table) = value {
+            table
+                .pairs::<T, Value<'lua>>()
+                .map(|res| res.map(|(k, _)| k))
+                .collect()
+        } else {
+            Err(Error::FromLuaConversionError {
+                from: value.type_name(),
+                to: "BTreeSet",
+                message: Some("expected table".to_string()),
+            })
+        }
+    }
+}
+
 impl<'lua, T: ToLua<'lua>> ToLua<'lua> for Option<T> {
     fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
         match self {

src/error.rs

@@ -105,6 +105,13 @@ pub enum Error {
     /// [`AnyUserData`]: struct.AnyUserData.html
     /// [`UserDataMethods`]: trait.UserDataMethods.html
     UserDataTypeMismatch,
+    /// An [`AnyUserData`] borrow failed because it has been destructed.
+    ///
+    /// This error can happen either due to to being destructed in a previous __gc, or due to being
+    /// destructed from exiting a `Lua::scope` call.
+    ///
+    /// [`AnyUserData`]: struct.AnyUserData.html
+    UserDataDestructed,
     /// An [`AnyUserData`] immutable borrow failed because it is already borrowed mutably.
     ///
     /// This error can occur when a method on a [`UserData`] type calls back into Lua, which then
@@ -132,6 +139,14 @@ pub enum Error {
         /// Original error returned by the Rust code.
         cause: Arc<Error>,
     },
+    /// Serialization error.
+    #[cfg(feature = "serialize")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
+    SerializeError(StdString),
+    /// Deserialization error.
+    #[cfg(feature = "serialize")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
+    DeserializeError(StdString),
     /// A custom error.
     ///
     /// This can be used for returning user-defined errors from callbacks.
@@ -206,6 +221,7 @@ impl fmt::Display for Error {
             }
             Error::CoroutineInactive => write!(fmt, "cannot resume inactive coroutine"),
             Error::UserDataTypeMismatch => write!(fmt, "userdata is not expected type"),
+            Error::UserDataDestructed => write!(fmt, "userdata has been destructed"),
             Error::UserDataBorrowError => write!(fmt, "userdata already mutably borrowed"),
             Error::UserDataBorrowMutError => write!(fmt, "userdata already borrowed"),
             Error::MismatchedRegistryKey => {
@@ -214,6 +230,14 @@ impl fmt::Display for Error {
             Error::CallbackError { ref traceback, .. } => {
                 write!(fmt, "callback error: {}", traceback)
             }
+            #[cfg(feature = "serialize")]
+            Error::SerializeError(ref err) => {
+                write!(fmt, "serialize error: {}", err)
+            },
+            #[cfg(feature = "serialize")]
+            Error::DeserializeError(ref err) => {
+                write!(fmt, "deserialize error: {}", err)
+            },
             Error::ExternalError(ref err) => write!(fmt, "{}", err),
         }
     }
@@ -289,3 +313,17 @@ impl std::convert::From<Utf8Error> for Error {
         Error::external(err)
     }
 }
+
+#[cfg(feature = "serialize")]
+impl serde::ser::Error for Error {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        Self::SerializeError(msg.to_string())
+    }
+}
+
+#[cfg(feature = "serialize")]
+impl serde::de::Error for Error {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        Self::DeserializeError(msg.to_string())
+    }
+}

src/ffi/lua.rs

@@ -38,7 +38,10 @@ pub use super::glue::LUA_REGISTRYINDEX;
 #[cfg(any(feature = "lua51", feature = "luajit"))]
 pub use super::glue::{LUA_ENVIRONINDEX, LUA_GLOBALSINDEX};
 
+#[cfg(not(feature = "luajit"))]
 pub const LUA_SIGNATURE: &[u8] = b"\x1bLua";
+#[cfg(feature = "luajit")]
+pub const LUA_SIGNATURE: &[u8] = b"\x1bLJ";
 
 // option for multiple returns in 'lua_pcall' and 'lua_call'
 pub const LUA_MULTRET: c_int = -1;

src/ffi/mod.rs

@@ -211,8 +211,8 @@ pub use self::lua::{
     LUA_HOOKCOUNT, LUA_HOOKLINE, LUA_HOOKRET, LUA_HOOKTAILCALL, LUA_MASKCALL, LUA_MASKCOUNT,
     LUA_MASKLINE, LUA_MASKRET, LUA_MINSTACK, LUA_MULTRET, LUA_OK, LUA_OPADD, LUA_OPDIV, LUA_OPEQ,
     LUA_OPLE, LUA_OPLT, LUA_OPMOD, LUA_OPMUL, LUA_OPPOW, LUA_OPSUB, LUA_OPUNM, LUA_REGISTRYINDEX,
-    LUA_TBOOLEAN, LUA_TFUNCTION, LUA_TLIGHTUSERDATA, LUA_TNIL, LUA_TNONE, LUA_TNUMBER, LUA_TSTRING,
-    LUA_TTABLE, LUA_TTHREAD, LUA_TUSERDATA, LUA_YIELD,
+    LUA_SIGNATURE, LUA_TBOOLEAN, LUA_TFUNCTION, LUA_TLIGHTUSERDATA, LUA_TNIL, LUA_TNONE,
+    LUA_TNUMBER, LUA_TSTRING, LUA_TTABLE, LUA_TTHREAD, LUA_TUSERDATA, LUA_YIELD,
 };
 
 #[cfg(any(feature = "lua54", feature = "lua53"))]

src/function.rs

@@ -1,5 +1,5 @@
-use std::os::raw::c_int;
-use std::ptr;
+use std::os::raw::{c_int, c_void};
+use std::{ptr, slice};
 
 use crate::error::{Error, Result};
 use crate::ffi;
@@ -119,6 +119,7 @@ impl<'lua> Function<'lua> {
     ///
     /// [`AsyncThread`]: struct.AsyncThread.html
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn call_async<'fut, A, R>(&self, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
@@ -205,6 +206,42 @@ impl<'lua> Function<'lua> {
             Ok(Function(lua.pop_ref()))
         }
     }
+
+    /// Dumps the function as a binary chunk.
+    ///
+    /// If `strip` is true, the binary representation may not include all debug information
+    /// about the function, to save space.
+    pub fn dump(&self, strip: bool) -> Result<Vec<u8>> {
+        unsafe extern "C" fn writer(
+            _state: *mut ffi::lua_State,
+            buf: *const c_void,
+            buf_len: usize,
+            data: *mut c_void,
+        ) -> c_int {
+            let data = &mut *(data as *mut Vec<u8>);
+            let buf = slice::from_raw_parts(buf as *const u8, buf_len);
+            data.extend_from_slice(buf);
+            0
+        }
+
+        let lua = self.0.lua;
+        let mut data: Vec<u8> = Vec::new();
+        unsafe {
+            let _sg = StackGuard::new(lua.state);
+            assert_stack(lua.state, 1);
+            lua.push_ref(&self.0);
+            let strip = if strip { 1 } else { 0 };
+            ffi::lua_dump(
+                lua.state,
+                writer,
+                &mut data as *mut Vec<u8> as *mut c_void,
+                strip,
+            );
+            ffi::lua_pop(lua.state, 1);
+        }
+
+        Ok(data)
+    }
 }
 
 impl<'lua> PartialEq for Function<'lua> {

src/hook.rs

@@ -37,7 +37,7 @@ impl<'a> Debug<'a> {
         }
     }
 
-    /// Corresponds to the `n` what mask.
+    /// Corresponds to the `S` what mask.
     pub fn source(&self) -> DebugSource<'a> {
         unsafe {
             mlua_assert!(

src/lib.rs

@@ -24,6 +24,18 @@
 //! The [`UserData`] trait can be implemented by user-defined types to make them available to Lua.
 //! Methods and operators to be used from Lua can be added using the [`UserDataMethods`] API.
 //!
+//! # Serde support
+//!
+//! The [`LuaSerdeExt`] trait implemented for [`Lua`] allows conversion from Rust types to Lua values
+//! and vice versa using serde. Any user defined data type that implements [`serde::Serialize`] or
+//! [`serde::Deserialize`] can be converted.
+//! For convenience, additional functionality to handle `NULL` values and arrays is provided.
+//!
+//! The [`Value`] enum implements [`serde::Serialize`] trait to support serializing Lua values
+//! (including [`UserData`]) into Rust values.
+//!
+//! Requires `feature = "serialize"`.
+//!
 //! # Async/await support
 //!
 //! The [`create_async_function`] allows creating non-blocking functions that returns [`Future`].
@@ -34,7 +46,7 @@
 //!
 //! # `Send` requirement
 //! By default `mlua` is `!Send`. This can be changed by enabling `feature = "send"` that adds `Send` requirement
-//! to `Function`s and [`UserData`].
+//! to [`Function`]s and [`UserData`].
 //!
 //! [Lua programming language]: https://www.lua.org/
 //! [`Lua`]: struct.Lua.html
@@ -45,16 +57,24 @@
 //! [`FromLua`]: trait.FromLua.html
 //! [`ToLuaMulti`]: trait.ToLuaMulti.html
 //! [`FromLuaMulti`]: trait.FromLuaMulti.html
+//! [`Function`]: struct.Function.html
 //! [`UserData`]: trait.UserData.html
 //! [`UserDataMethods`]: trait.UserDataMethods.html
+//! [`LuaSerdeExt`]: serde/trait.LuaSerdeExt.html
+//! [`Value`]: enum.Value.html
 //! [`create_async_function`]: struct.Lua.html#method.create_async_function
 //! [`call_async`]: struct.Function.html#method.call_async
 //! [`AsyncThread`]: struct.AsyncThread.html
 //! [`Future`]: ../futures_core/future/trait.Future.html
+//! [`serde::Serialize`]: https://docs.serde.rs/serde/ser/trait.Serialize.html
+//! [`serde::Deserialize`]: https://docs.serde.rs/serde/de/trait.Deserialize.html
 
+// mlua types in rustdoc of other crates get linked to here.
+#![doc(html_root_url = "https://docs.rs/mlua/0.5.0")]
 // Deny warnings inside doc tests / examples. When this isn't present, rustdoc doesn't show *any*
 // warnings at all.
 #![doc(test(attr(deny(warnings))))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[macro_use]
 mod macros;
@@ -81,7 +101,7 @@ pub use crate::ffi::lua_State;
 pub use crate::error::{Error, ExternalError, ExternalResult, Result};
 pub use crate::function::Function;
 pub use crate::hook::{Debug, DebugNames, DebugSource, DebugStack, HookTriggers};
-pub use crate::lua::{Chunk, GCMode, Lua};
+pub use crate::lua::{Chunk, ChunkMode, GCMode, Lua};
 pub use crate::multi::Variadic;
 pub use crate::scope::Scope;
 pub use crate::stdlib::StdLib;
@@ -95,4 +115,19 @@ pub use crate::value::{FromLua, FromLuaMulti, MultiValue, Nil, ToLua, ToLuaMulti
 #[cfg(feature = "async")]
 pub use crate::thread::AsyncThread;
 
+#[cfg(feature = "serialize")]
+pub use crate::serde::LuaSerdeExt;
+
 pub mod prelude;
+#[cfg(feature = "serialize")]
+#[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
+pub mod serde;
+
+// Re-export #[mlua_derive::lua_module].
+#[cfg(feature = "mlua_derive")]
+#[allow(unused_imports)]
+#[macro_use]
+extern crate mlua_derive;
+#[cfg(feature = "mlua_derive")]
+#[doc(hidden)]
+pub use mlua_derive::*;

src/lua.rs

@@ -1,6 +1,6 @@
 use std::any::TypeId;
 use std::cell::{RefCell, UnsafeCell};
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::ffi::CString;
 use std::marker::PhantomData;
 use std::os::raw::{c_char, c_int, c_void};
@@ -18,8 +18,9 @@ use crate::table::Table;
 use crate::thread::Thread;
 use crate::types::{
     Callback, HookCallback, Integer, LightUserData, LuaRef, MaybeSend, Number, RegistryKey,
+    UserDataCell,
 };
-use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods};
+use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods, UserDataWrapped};
 use crate::util::{
     assert_stack, callback_error, check_stack, get_gc_userdata, get_main_state,
     get_meta_gc_userdata, get_wrapped_error, init_error_registry, init_gc_metatable_for,
@@ -39,6 +40,9 @@ use {
     futures_util::future::{self, TryFutureExt},
 };
 
+#[cfg(feature = "serialize")]
+use {crate::util::get_destructed_userdata_metatable, serde::Serialize};
+
 /// Top level Lua struct which holds the Lua state itself.
 pub struct Lua {
     pub(crate) state: *mut ffi::lua_State,
@@ -53,8 +57,10 @@ pub struct Lua {
 // Data associated with the lua_State.
 struct ExtraData {
     registered_userdata: HashMap<TypeId, c_int>,
+    registered_userdata_mt: HashSet<isize>,
     registry_unref_list: Arc<Mutex<Option<Vec<c_int>>>>,
 
+    libs: StdLib,
     mem_info: *mut MemoryInfo,
 
     ref_thread: *mut ffi::lua_State,
@@ -94,19 +100,22 @@ pub(crate) static EXTRA_REGISTRY_KEY: u8 = 0;
 
 /// Requires `feature = "send"`
 #[cfg(feature = "send")]
+#[cfg_attr(docsrs, doc(cfg(feature = "send")))]
 unsafe impl Send for Lua {}
 
 impl Drop for Lua {
     fn drop(&mut self) {
         unsafe {
             if !self.ephemeral {
-                let mut extra = mlua_expect!(self.extra.lock(), "extra is poisoned");
+                let extra = mlua_expect!(self.extra.lock(), "extra is poisoned");
                 mlua_debug_assert!(
                     ffi::lua_gettop(extra.ref_thread) == extra.ref_stack_max
                         && extra.ref_stack_max as usize == extra.ref_free.len(),
                     "reference leak detected"
                 );
-                *mlua_expect!(extra.registry_unref_list.lock(), "unref list poisoned") = None;
+                let mut unref_list =
+                    mlua_expect!(extra.registry_unref_list.lock(), "unref list poisoned");
+                *unref_list = None;
                 ffi::lua_close(self.main_state.expect("main_state is null"));
                 if !extra.mem_info.is_null() {
                     Box::from_raw(extra.mem_info);
@@ -164,7 +173,9 @@ impl Lua {
 
         let mut lua = unsafe { Self::unsafe_new_with(libs) };
 
-        mlua_expect!(lua.disable_c_modules(), "Error during disabling C modules");
+        if libs.contains(StdLib::PACKAGE) {
+            mlua_expect!(lua.disable_c_modules(), "Error during disabling C modules");
+        }
         lua.safe = true;
 
         Ok(lua)
@@ -254,7 +265,7 @@ impl Lua {
         lua.ephemeral = false;
         #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
         {
-            lua.extra.lock().unwrap().mem_info = mem_info;
+            mlua_expect!(lua.extra.lock(), "extra is poisoned").mem_info = mem_info;
         }
 
         mlua_expect!(
@@ -263,6 +274,7 @@ impl Lua {
             }),
             "Error during loading standard libraries"
         );
+        mlua_expect!(lua.extra.lock(), "extra is poisoned").libs |= libs;
 
         lua
     }
@@ -292,6 +304,10 @@ impl Lua {
                     init_gc_metatable_for::<Waker>(state, None);
                 }
 
+                // Init serde metatables
+                #[cfg(feature = "serialize")]
+                crate::serde::init_metatables(state);
+
                 // Create ref stack thread and place it in the registry to prevent it from being garbage
                 // collected.
 
@@ -306,8 +322,10 @@ impl Lua {
 
         let extra = Arc::new(Mutex::new(ExtraData {
             registered_userdata: HashMap::new(),
+            registered_userdata_mt: HashSet::new(),
             registry_unref_list: Arc::new(Mutex::new(Some(Vec::new()))),
             ref_thread,
+            libs: StdLib::NONE,
             mem_info: ptr::null_mut(),
             // We need 1 extra stack space to move values in and out of the ref stack.
             ref_stack_size: ffi::LUA_MINSTACK - 1,
@@ -368,11 +386,20 @@ impl Lua {
         }
 
         let state = self.main_state.unwrap_or(self.state);
-        unsafe {
+        let res = unsafe {
             protect_lua_closure(state, 0, 0, |state| {
                 load_from_std_lib(state, libs);
             })
+        };
+
+        // If `package` library loaded into a safe lua state then disable C modules
+        let curr_libs = mlua_expect!(self.extra.lock(), "extra is poisoned").libs;
+        if self.safe && (curr_libs ^ (curr_libs | libs)).contains(StdLib::PACKAGE) {
+            mlua_expect!(self.disable_c_modules(), "Error during disabling C modules");
         }
+        mlua_expect!(self.extra.lock(), "extra is poisoned").libs |= libs;
+
+        res
     }
 
     /// Consumes and leaks `Lua` object, returning a static reference `&'static Lua`.
@@ -490,7 +517,7 @@ impl Lua {
         unsafe { (*extra.mem_info).used_memory as usize }
     }
 
-    /// Sets a memory limit on this Lua state.
+    /// Sets a memory limit (in bytes) on this Lua state.
     ///
     /// Once an allocation occurs that would pass this memory limit,
     /// a `Error::MemoryError` is generated instead.
@@ -658,6 +685,9 @@ impl Lua {
     /// similar on the returned builder.  Code is not even parsed until one of these methods is
     /// called.
     ///
+    /// If this `Lua` was created with `unsafe_new`, `load` will automatically detect and load
+    /// chunks of either text or binary type, as if passing `bt` mode to `luaL_loadbufferx`.
+    ///
     /// [`Chunk::exec`]: struct.Chunk.html#method.exec
     pub fn load<'lua, 'a, S>(&'lua self, source: &'a S) -> Chunk<'lua, 'a>
     where
@@ -668,6 +698,7 @@ impl Lua {
             source: source.as_ref(),
             name: None,
             env: None,
+            mode: None,
         }
     }
 
@@ -676,28 +707,35 @@ impl Lua {
         source: &[u8],
         name: Option<&CString>,
         env: Option<Value<'lua>>,
+        mode: Option<ChunkMode>,
     ) -> Result<Function<'lua>> {
         unsafe {
             let _sg = StackGuard::new(self.state);
             assert_stack(self.state, 1);
 
-            match if let Some(name) = name {
-                ffi::luaL_loadbufferx(
-                    self.state,
-                    source.as_ptr() as *const c_char,
-                    source.len(),
-                    name.as_ptr() as *const c_char,
-                    cstr!("t"),
-                )
-            } else {
-                ffi::luaL_loadbufferx(
-                    self.state,
-                    source.as_ptr() as *const c_char,
-                    source.len(),
-                    ptr::null(),
-                    cstr!("t"),
-                )
-            } {
+            let mode_str = match mode {
+                Some(ChunkMode::Binary) if self.safe => {
+                    return Err(Error::SafetyError(
+                        "binary chunks are disabled in safe mode".to_string(),
+                    ))
+                }
+                Some(ChunkMode::Binary) => cstr!("b"),
+                Some(ChunkMode::Text) => cstr!("t"),
+                None if source.starts_with(ffi::LUA_SIGNATURE) && self.safe => {
+                    return Err(Error::SafetyError(
+                        "binary chunks are disabled in safe mode".to_string(),
+                    ))
+                }
+                None => cstr!("bt"),
+            };
+
+            match ffi::luaL_loadbufferx(
+                self.state,
+                source.as_ptr() as *const c_char,
+                source.len(),
+                name.map(|n| n.as_ptr()).unwrap_or_else(ptr::null),
+                mode_str,
+            ) {
                 ffi::LUA_OK => {
                     if let Some(env) = env {
                         self.push_value(env)?;
@@ -728,7 +766,7 @@ impl Lua {
         }
     }
 
-    /// Creates and returns a new table.
+    /// Creates and returns a new empty table.
     pub fn create_table(&self) -> Result<Table> {
         unsafe {
             let _sg = StackGuard::new(self.state);
@@ -742,6 +780,21 @@ impl Lua {
         }
     }
 
+    /// Creates and returns a new empty table, with the specified capacity.
+    /// `narr` is a hint for how many elements the table will have as a sequence;
+    /// `nrec` is a hint for how many other elements the table will have.
+    /// Lua may use these hints to preallocate memory for the new table.
+    pub fn create_table_with_capacity(&self, narr: c_int, nrec: c_int) -> Result<Table> {
+        unsafe {
+            let _sg = StackGuard::new(self.state);
+            assert_stack(self.state, 4);
+            protect_lua_closure(self.state, 0, 1, |state| {
+                ffi::lua_createtable(state, narr, nrec)
+            })?;
+            Ok(Table(self.pop_ref()))
+        }
+    }
+
     /// Creates a table and fills it with values from an iterator.
     pub fn create_table_from<'lua, K, V, I>(&'lua self, cont: I) -> Result<Table<'lua>>
     where
@@ -903,8 +956,9 @@ impl Lua {
     /// ```
     ///
     /// [`Thread`]: struct.Thread.html
-    /// [`ThreadStream`]: struct.ThreadStream.html
+    /// [`AsyncThread`]: struct.AsyncThread.html
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn create_async_function<'lua, 'callback, A, R, F, FR>(
         &'lua self,
         func: F,
@@ -947,7 +1001,19 @@ impl Lua {
     where
         T: 'static + MaybeSend + UserData,
     {
-        unsafe { self.make_userdata(data) }
+        unsafe { self.make_userdata(UserDataWrapped::new(data)) }
+    }
+
+    /// Create a Lua userdata object from a custom serializable userdata type.
+    ///
+    /// Requires `feature = "serialize"`
+    #[cfg(feature = "serialize")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
+    pub fn create_ser_userdata<T>(&self, data: T) -> Result<AnyUserData>
+    where
+        T: 'static + MaybeSend + UserData + Serialize,
+    {
+        unsafe { self.make_userdata(UserDataWrapped::new_ser(data)) }
     }
 
     /// Returns a handle to the global environment.
@@ -1008,6 +1074,7 @@ impl Lua {
     ///
     /// [`scope`]: #method.scope
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn async_scope<'lua, 'scope, R, F, FR>(
         &'lua self,
         f: F,
@@ -1274,11 +1341,10 @@ impl Lua {
     /// by `Lua::remove_registry_value`.
     pub fn expire_registry_values(&self) {
         unsafe {
-            let mut extra = mlua_expect!(self.extra.lock(), "extra is poisoned");
-            let unref_list = mem::replace(
-                &mut *mlua_expect!(extra.registry_unref_list.lock(), "unref list poisoned"),
-                Some(Vec::new()),
-            );
+            let extra = mlua_expect!(self.extra.lock(), "extra is poisoned");
+            let mut unref_list =
+                mlua_expect!(extra.registry_unref_list.lock(), "unref list poisoned");
+            let unref_list = mem::replace(&mut *unref_list, Some(Vec::new()));
             for id in mlua_expect!(unref_list, "unref list not set") {
                 ffi::luaL_unref(self.state, ffi::LUA_REGISTRYINDEX, id);
             }
@@ -1469,7 +1535,7 @@ impl Lua {
         let no_methods = methods.methods.is_empty();
 
         if no_methods {
-            init_userdata_metatable::<RefCell<T>>(self.state, -1, None)?;
+            init_userdata_metatable::<UserDataCell<T>>(self.state, -1, None)?;
         } else {
             protect_lua_closure(self.state, 0, 1, |state| {
                 ffi::lua_newtable(state);
@@ -1490,21 +1556,49 @@ impl Lua {
                 })?;
             }
 
-            init_userdata_metatable::<RefCell<T>>(self.state, -2, Some(-1))?;
+            init_userdata_metatable::<UserDataCell<T>>(self.state, -2, Some(-1))?;
             ffi::lua_pop(self.state, 1);
         }
 
-        let id = protect_lua_closure(self.state, 1, 0, |state| {
-            ffi::luaL_ref(state, ffi::LUA_REGISTRYINDEX)
+        let (ptr, id) = protect_lua_closure(self.state, 1, 0, |state| {
+            let ptr = ffi::lua_topointer(state, -1) as isize;
+            let id = ffi::luaL_ref(state, ffi::LUA_REGISTRYINDEX);
+            (ptr, id)
         })?;
 
-        mlua_expect!(self.extra.lock(), "extra is poisoned")
-            .registered_userdata
-            .insert(TypeId::of::<T>(), id);
+        let mut extra = mlua_expect!(self.extra.lock(), "extra is poisoned");
+        extra.registered_userdata.insert(TypeId::of::<T>(), id);
+        extra.registered_userdata_mt.insert(ptr);
 
         Ok(id)
     }
 
+    // Pushes a LuaRef value onto the stack, checking that it's any registered userdata
+    // Uses 2 stack spaces, does not call checkstack
+    #[cfg(feature = "serialize")]
+    pub(crate) unsafe fn push_userdata_ref(&self, lref: &LuaRef) -> Result<()> {
+        self.push_ref(lref);
+        if ffi::lua_getmetatable(self.state, -1) == 0 {
+            Err(Error::UserDataTypeMismatch)
+        } else {
+            // Check that this is our metatable
+            let ptr = ffi::lua_topointer(self.state, -1) as isize;
+            let extra = mlua_expect!(self.extra.lock(), "extra is poisoned");
+            if !extra.registered_userdata_mt.contains(&ptr) {
+                // Maybe UserData destructed?
+                get_destructed_userdata_metatable(self.state);
+                if ffi::lua_rawequal(self.state, -1, -2) == 1 {
+                    Err(Error::UserDataDestructed)
+                } else {
+                    Err(Error::UserDataTypeMismatch)
+                }
+            } else {
+                ffi::lua_pop(self.state, 1);
+                Ok(())
+            }
+        }
+    }
+
     // Creates a Function out of a Callback containing a 'static Fn.  This is safe ONLY because the
     // Fn is 'static, otherwise it could capture 'callback arguments improperly.  Without ATCs, we
     // cannot easily deal with the "correct" callback type of:
@@ -1578,7 +1672,12 @@ impl Lua {
         'lua: 'callback,
     {
         #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
-        self.load_from_std_lib(StdLib::COROUTINE)?;
+        {
+            let libs = mlua_expect!(self.extra.lock(), "extra is poisoned").libs;
+            if !libs.contains(StdLib::COROUTINE) {
+                self.load_from_std_lib(StdLib::COROUTINE)?;
+            }
+        }
 
         unsafe extern "C" fn call_callback(state: *mut ffi::lua_State) -> c_int {
             callback_error(state, |nargs| {
@@ -1705,7 +1804,7 @@ impl Lua {
         .into_function()
     }
 
-    pub(crate) unsafe fn make_userdata<T>(&self, data: T) -> Result<AnyUserData>
+    pub(crate) unsafe fn make_userdata<T>(&self, data: UserDataWrapped<T>) -> Result<AnyUserData>
     where
         T: 'static + UserData,
     {
@@ -1713,7 +1812,7 @@ impl Lua {
         assert_stack(self.state, 4);
 
         let ud_index = self.userdata_metatable::<T>()?;
-        push_userdata::<RefCell<T>>(self.state, RefCell::new(data))?;
+        push_userdata::<UserDataCell<T>>(self.state, RefCell::new(data))?;
 
         ffi::lua_rawgeti(
             self.state,
@@ -1802,6 +1901,14 @@ pub struct Chunk<'lua, 'a> {
     source: &'a [u8],
     name: Option<CString>,
     env: Option<Value<'lua>>,
+    mode: Option<ChunkMode>,
+}
+
+/// Represents chunk mode (text or binary).
+#[derive(Clone, Copy)]
+pub enum ChunkMode {
+    Text,
+    Binary,
 }
 
 impl<'lua, 'a> Chunk<'lua, 'a> {
@@ -1833,6 +1940,17 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
         Ok(self)
     }
 
+    /// Sets whether the chunk is text or binary (autodetected by default).
+    ///
+    /// Lua does not check the consistency of binary chunks, therefore this mode is allowed only
+    /// for instances created with [`Lua::unsafe_new`].
+    ///
+    /// [`Lua::unsafe_new`]: struct.Lua.html#method.unsafe_new
+    pub fn set_mode(mut self, mode: ChunkMode) -> Chunk<'lua, 'a> {
+        self.mode = Some(mode);
+        self
+    }
+
     /// Execute this chunk of code.
     ///
     /// This is equivalent to calling the chunk function with no arguments and no return values.
@@ -1849,6 +1967,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     ///
     /// [`Chunk::exec`]: struct.Chunk.html#method.exec
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn exec_async<'fut>(self) -> LocalBoxFuture<'fut, Result<()>>
     where
         'lua: 'fut,
@@ -1862,13 +1981,17 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     /// the value that it evaluates to.  Otherwise, the chunk is interpreted as a block as normal,
     /// and this is equivalent to calling `exec`.
     pub fn eval<R: FromLuaMulti<'lua>>(self) -> Result<R> {
-        // First, try interpreting the lua as an expression by adding
+        // Bytecode is always interpreted as a statement.
+        // For source code, first try interpreting the lua as an expression by adding
         // "return", then as a statement.  This is the same thing the
         // actual lua repl does.
-        if let Ok(function) = self.lua.load_chunk(
+        if self.source.starts_with(ffi::LUA_SIGNATURE) {
+            self.call(())
+        } else if let Ok(function) = self.lua.load_chunk(
             &self.expression_source(),
             self.name.as_ref(),
             self.env.clone(),
+            self.mode,
         ) {
             function.call(())
         } else {
@@ -1884,15 +2007,19 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     ///
     /// [`Chunk::eval`]: struct.Chunk.html#method.eval
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn eval_async<'fut, R>(self) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
         R: FromLuaMulti<'lua> + 'fut,
     {
-        if let Ok(function) = self.lua.load_chunk(
+        if self.source.starts_with(ffi::LUA_SIGNATURE) {
+            self.call_async(())
+        } else if let Ok(function) = self.lua.load_chunk(
             &self.expression_source(),
             self.name.as_ref(),
             self.env.clone(),
+            self.mode,
         ) {
             function.call_async(())
         } else {
@@ -1915,6 +2042,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     ///
     /// [`Chunk::call`]: struct.Chunk.html#method.call
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn call_async<'fut, A, R>(self, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
@@ -1932,7 +2060,7 @@ impl<'lua, 'a> Chunk<'lua, 'a> {
     /// This simply compiles the chunk without actually executing it.
     pub fn into_function(self) -> Result<Function<'lua>> {
         self.lua
-            .load_chunk(self.source, self.name.as_ref(), self.env)
+            .load_chunk(self.source, self.name.as_ref(), self.env, self.mode)
     }
 
     fn expression_source(&self) -> Vec<u8> {

src/scope.rs

@@ -1,16 +1,19 @@
 use std::any::Any;
-use std::cell::{Cell, RefCell};
+use std::cell::{Cell, Ref, RefCell, RefMut};
 use std::marker::PhantomData;
 use std::mem;
 use std::os::raw::c_void;
 use std::rc::Rc;
 
+#[cfg(feature = "serialize")]
+use serde::Serialize;
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
 use crate::lua::Lua;
-use crate::types::{Callback, LuaRef, MaybeSend};
-use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods};
+use crate::types::{Callback, LuaRef, MaybeSend, UserDataCell};
+use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataMethods, UserDataWrapped};
 use crate::util::{
     assert_stack, init_userdata_metatable, protect_lua_closure, push_string, push_userdata,
     take_userdata, StackGuard,
@@ -112,6 +115,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
     /// [`Lua::scope`]: struct.Lua.html#method.scope
     /// [`Lua::async_scope`]: struct.Lua.html#method.async_scope
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn create_async_function<'callback, A, R, F, FR>(
         &'callback self,
         func: F,
@@ -143,6 +147,33 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
     /// [`Lua::create_userdata`]: struct.Lua.html#method.create_userdata
     /// [`Lua::scope`]: struct.Lua.html#method.scope
     pub fn create_userdata<T>(&self, data: T) -> Result<AnyUserData<'lua>>
+    where
+        T: 'static + UserData,
+    {
+        self.create_userdata_inner(UserDataWrapped::new(data))
+    }
+
+    /// Create a Lua userdata object from a custom serializable userdata type.
+    ///
+    /// This is a version of [`Lua::create_ser_userdata`] that creates a userdata which expires on
+    /// scope drop, and does not require that the userdata type be Send (but still requires that the
+    /// UserData be 'static).
+    /// See [`Lua::scope`] for more details.
+    ///
+    /// Requires `feature = "serialize"`
+    ///
+    /// [`Lua::create_ser_userdata`]: struct.Lua.html#method.create_ser_userdata
+    /// [`Lua::scope`]: struct.Lua.html#method.scope
+    #[cfg(feature = "serialize")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
+    pub fn create_ser_userdata<T>(&self, data: T) -> Result<AnyUserData<'lua>>
+    where
+        T: 'static + UserData + Serialize,
+    {
+        self.create_userdata_inner(UserDataWrapped::new_ser(data))
+    }
+
+    fn create_userdata_inner<T>(&self, data: UserDataWrapped<T>) -> Result<AnyUserData<'lua>>
     where
         T: 'static + UserData,
     {
@@ -156,7 +187,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
                 u.lua.push_ref(&u);
                 // We know the destructor has not run yet because we hold a reference to the
                 // userdata.
-                vec![Box::new(take_userdata::<RefCell<T>>(state))]
+                vec![Box::new(take_userdata::<UserDataCell<T>>(state))]
             }));
             Ok(u)
         }
@@ -189,7 +220,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
     where
         T: 'scope + UserData,
     {
-        let data = Rc::new(RefCell::new(data));
+        let data = Rc::new(RefCell::new(UserDataWrapped::new(data)));
 
         // 'callback outliving 'scope is a lie to make the types work out, required due to the
         // inability to work with the more correct callback type that is universally quantified over
@@ -198,7 +229,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
         // parameters.
         fn wrap_method<'scope, 'lua, 'callback: 'scope, T: 'scope>(
             scope: &Scope<'lua, 'scope>,
-            data: Rc<RefCell<T>>,
+            data: Rc<UserDataCell<T>>,
             method: NonStaticMethod<'callback, T>,
         ) -> Result<Function<'lua>> {
             // On methods that actually receive the userdata, we fake a type check on the passed in
@@ -210,20 +241,18 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             // first argument).
             let check_data = data.clone();
             let check_ud_type = move |lua: &'callback Lua, value| {
-                if let Some(value) = value {
-                    if let Value::UserData(u) = value {
-                        unsafe {
-                            assert_stack(lua.state, 1);
-                            lua.push_ref(&u.0);
-                            ffi::lua_getuservalue(lua.state, -1);
-                            #[cfg(any(feature = "lua52", feature = "lua51", feature = "luajit"))]
-                            {
-                                ffi::lua_rawgeti(lua.state, -1, 1);
-                                ffi::lua_remove(lua.state, -2);
-                            }
-                            return ffi::lua_touserdata(lua.state, -1)
-                                == check_data.as_ptr() as *mut c_void;
+                if let Some(Value::UserData(ud)) = value {
+                    unsafe {
+                        assert_stack(lua.state, 1);
+                        lua.push_ref(&ud.0);
+                        ffi::lua_getuservalue(lua.state, -1);
+                        #[cfg(any(feature = "lua52", feature = "lua51", feature = "luajit"))]
+                        {
+                            ffi::lua_rawgeti(lua.state, -1, 1);
+                            ffi::lua_remove(lua.state, -2);
                         }
+                        return ffi::lua_touserdata(lua.state, -1)
+                            == check_data.as_ptr() as *mut c_void;
                     }
                 }
 
@@ -236,7 +265,10 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
                         if !check_ud_type(lua, args.pop_front()) {
                             return Err(Error::UserDataTypeMismatch);
                         }
-                        let data = data.try_borrow().map_err(|_| Error::UserDataBorrowError)?;
+                        let data = data
+                            .try_borrow()
+                            .map(|cell| Ref::map(cell, AsRef::as_ref))
+                            .map_err(|_| Error::UserDataBorrowError)?;
                         method(lua, &*data, args)
                     });
                     unsafe { scope.create_callback(f) }
@@ -252,6 +284,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
                             .map_err(|_| Error::RecursiveMutCallback)?;
                         let mut data = data
                             .try_borrow_mut()
+                            .map(|cell| RefMut::map(cell, AsMut::as_mut))
                             .map_err(|_| Error::UserDataBorrowMutError)?;
                         (&mut *method)(lua, &mut *data, args)
                     });

src/serde/de.rs

@@ -0,0 +1,327 @@
+use std::string::String as StdString;
+
+use serde::de::{self, IntoDeserializer};
+
+use crate::error::{Error, Result};
+use crate::table::{TablePairs, TableSequence};
+use crate::value::Value;
+
+/// A struct for deserializing Lua values into Rust values.
+pub struct Deserializer<'lua>(pub Value<'lua>);
+
+impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
+    type Error = Error;
+
+    #[inline]
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.0 {
+            Value::Nil => visitor.visit_unit(),
+            Value::Boolean(b) => visitor.visit_bool(b),
+            Value::Integer(i) => visitor.visit_i64(i),
+            Value::Number(n) => visitor.visit_f64(n),
+            Value::String(s) => match s.to_str() {
+                Ok(s) => visitor.visit_str(s),
+                Err(_) => visitor.visit_bytes(s.as_bytes()),
+            },
+            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::Function(_)
+            | Value::Thread(_)
+            | Value::UserData(_)
+            | Value::LightUserData(_)
+            | Value::Error(_) => Err(de::Error::custom("invalid value type")),
+        }
+    }
+
+    #[inline]
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.0 {
+            Value::Nil => visitor.visit_none(),
+            Value::LightUserData(ud) if ud.0.is_null() => visitor.visit_none(),
+            _ => visitor.visit_some(self),
+        }
+    }
+
+    #[inline]
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let (variant, value) = match self.0 {
+            Value::Table(value) => {
+                let mut iter = value.pairs::<StdString, Value>();
+                let (variant, value) = match iter.next() {
+                    Some(v) => v?,
+                    None => {
+                        return Err(de::Error::invalid_value(
+                            de::Unexpected::Map,
+                            &"map with a single key",
+                        ))
+                    }
+                };
+
+                if iter.next().is_some() {
+                    return Err(de::Error::invalid_value(
+                        de::Unexpected::Map,
+                        &"map with a single key",
+                    ));
+                }
+                (variant, Some(value))
+            }
+            Value::String(variant) => (variant.to_str()?.to_owned(), None),
+            _ => return Err(de::Error::custom("bad enum value")),
+        };
+
+        visitor.visit_enum(EnumDeserializer { variant, value })
+    }
+
+    #[inline]
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.0 {
+            Value::Table(t) => {
+                let len = t.raw_len() as usize;
+                let mut deserializer = SeqDeserializer(t.raw_sequence_values());
+                let seq = visitor.visit_seq(&mut deserializer)?;
+                if deserializer.0.count() == 0 {
+                    Ok(seq)
+                } else {
+                    Err(de::Error::invalid_length(
+                        len,
+                        &"fewer elements in the table",
+                    ))
+                }
+            }
+            _ => Err(de::Error::custom("invalid value type")),
+        }
+    }
+
+    #[inline]
+    fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    #[inline]
+    fn deserialize_tuple_struct<V>(
+        self,
+        _name: &'static str,
+        _len: usize,
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    #[inline]
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.0 {
+            Value::Table(t) => {
+                let mut deserializer = MapDeserializer::new(t.pairs());
+                let map = visitor.visit_map(&mut deserializer)?;
+                let count = deserializer.pairs.count();
+                if count == 0 {
+                    Ok(map)
+                } else {
+                    Err(de::Error::invalid_length(
+                        deserializer.processed + count,
+                        &"fewer elements in the table",
+                    ))
+                }
+            }
+            _ => Err(de::Error::custom("invalid value type")),
+        }
+    }
+
+    #[inline]
+    fn deserialize_struct<V>(
+        self,
+        _name: &'static str,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_map(visitor)
+    }
+
+    serde::forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 u8 u16 u32 u64 f32 f64 char str string bytes
+        byte_buf unit unit_struct newtype_struct
+        identifier ignored_any
+    }
+}
+
+struct SeqDeserializer<'lua>(TableSequence<'lua, Value<'lua>>);
+
+impl<'lua, 'de> de::SeqAccess<'de> for SeqDeserializer<'lua> {
+    type Error = Error;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.0.next() {
+            Some(value) => seed.deserialize(Deserializer(value?)).map(Some),
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.0.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+struct MapDeserializer<'lua> {
+    pairs: TablePairs<'lua, Value<'lua>, Value<'lua>>,
+    value: Option<Value<'lua>>,
+    processed: usize,
+}
+
+impl<'lua> MapDeserializer<'lua> {
+    fn new(pairs: TablePairs<'lua, Value<'lua>, Value<'lua>>) -> Self {
+        MapDeserializer {
+            pairs,
+            value: None,
+            processed: 0,
+        }
+    }
+}
+
+impl<'lua, 'de> de::MapAccess<'de> for MapDeserializer<'lua> {
+    type Error = Error;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.pairs.next() {
+            Some(item) => {
+                let (key, value) = item?;
+                self.processed += 1;
+                self.value = Some(value);
+                let key_de = Deserializer(key);
+                seed.deserialize(key_de).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.value.take() {
+            Some(value) => seed.deserialize(Deserializer(value)),
+            None => Err(de::Error::custom("value is missing")),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.pairs.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+struct EnumDeserializer<'lua> {
+    variant: StdString,
+    value: Option<Value<'lua>>,
+}
+
+impl<'lua, 'de> de::EnumAccess<'de> for EnumDeserializer<'lua> {
+    type Error = Error;
+    type Variant = VariantDeserializer<'lua>;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant)>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        let variant = self.variant.into_deserializer();
+        let variant_access = VariantDeserializer { value: self.value };
+        seed.deserialize(variant).map(|v| (v, variant_access))
+    }
+}
+
+struct VariantDeserializer<'lua> {
+    value: Option<Value<'lua>>,
+}
+
+impl<'lua, 'de> de::VariantAccess<'de> for VariantDeserializer<'lua> {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<()> {
+        match self.value {
+            Some(_) => Err(de::Error::invalid_type(
+                de::Unexpected::NewtypeVariant,
+                &"unit variant",
+            )),
+            None => Ok(()),
+        }
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.value {
+            Some(value) => seed.deserialize(Deserializer(value)),
+            None => Err(de::Error::invalid_type(
+                de::Unexpected::UnitVariant,
+                &"newtype variant",
+            )),
+        }
+    }
+
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Some(value) => serde::Deserializer::deserialize_seq(Deserializer(value), visitor),
+            None => Err(de::Error::invalid_type(
+                de::Unexpected::UnitVariant,
+                &"tuple variant",
+            )),
+        }
+    }
+
+    fn struct_variant<V>(self, _fields: &'static [&'static str], visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Some(value) => serde::Deserializer::deserialize_map(Deserializer(value), visitor),
+            None => Err(de::Error::invalid_type(
+                de::Unexpected::UnitVariant,
+                &"struct variant",
+            )),
+        }
+    }
+}

src/serde/mod.rs

@@ -0,0 +1,200 @@
+//! (De)Serialization support using serde.
+
+use std::os::raw::{c_int, c_void};
+use std::ptr;
+
+use serde::{Deserialize, Serialize};
+
+use crate::error::Result;
+use crate::ffi;
+use crate::lua::Lua;
+use crate::table::Table;
+use crate::util::{assert_stack, protect_lua, StackGuard};
+use crate::value::Value;
+
+pub trait LuaSerdeExt<'lua> {
+    /// A special value (lightuserdata) to encode/decode optional (none) values.
+    ///
+    /// Requires `feature = "serialize"`
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use std::collections::HashMap;
+    /// use mlua::{Lua, Result, LuaSerdeExt};
+    ///
+    /// fn main() -> Result<()> {
+    ///     let lua = Lua::new();
+    ///     lua.globals().set("null", lua.null()?)?;
+    ///
+    ///     let val = lua.load(r#"{a = null}"#).eval()?;
+    ///     let map: HashMap<String, Option<String>> = lua.from_value(val)?;
+    ///     assert_eq!(map["a"], None);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    fn null(&'lua self) -> Result<Value<'lua>>;
+
+    /// 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
+    /// as the `#` operator on that table.
+    ///
+    /// Requires `feature = "serialize"`
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use mlua::{Lua, Result, LuaSerdeExt};
+    /// use serde_json::Value as JsonValue;
+    ///
+    /// fn main() -> Result<()> {
+    ///     let lua = Lua::new();
+    ///     lua.globals().set("array_mt", lua.array_metatable()?)?;
+    ///
+    ///     // Encode as an empty array (no sequence part in the lua table)
+    ///     let val = lua.load("setmetatable({a = 5}, array_mt)").eval()?;
+    ///     let j: JsonValue = lua.from_value(val)?;
+    ///     assert_eq!(j.to_string(), "[]");
+    ///
+    ///     // Encode as object
+    ///     let val = lua.load("{a = 5}").eval()?;
+    ///     let j: JsonValue = lua.from_value(val)?;
+    ///     assert_eq!(j.to_string(), r#"{"a":5}"#);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    fn array_metatable(&'lua self) -> Result<Table<'lua>>;
+
+    /// Converts `T` into a `Value` instance.
+    ///
+    /// Requires `feature = "serialize"`
+    ///
+    /// [`Value`]: enum.Value.html
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use mlua::{Lua, Result, LuaSerdeExt};
+    /// use serde::Serialize;
+    ///
+    /// #[derive(Serialize)]
+    /// struct User {
+    ///     name: String,
+    ///     age: u8,
+    /// }
+    ///
+    /// fn main() -> Result<()> {
+    ///     let lua = Lua::new();
+    ///     let u = User {
+    ///         name: "John Smith".into(),
+    ///         age: 20,
+    ///     };
+    ///     lua.globals().set("user", lua.to_value(&u)?)?;
+    ///     lua.load(r#"
+    ///         assert(user["name"] == "John Smith")
+    ///         assert(user["age"] == 20)
+    ///     "#).exec()
+    /// }
+    /// ```
+    fn to_value<T: Serialize + ?Sized>(&'lua self, t: &T) -> Result<Value<'lua>>;
+
+    /// Deserializes a `Value` into any serde deserializable object.
+    ///
+    /// Requires `feature = "serialize"`
+    ///
+    /// [`Value`]: enum.Value.html
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use mlua::{Lua, Result, LuaSerdeExt};
+    /// use serde::Deserialize;
+    ///
+    /// #[derive(Deserialize, Debug, PartialEq)]
+    /// struct User {
+    ///     name: String,
+    ///     age: u8,
+    /// }
+    ///
+    /// fn main() -> Result<()> {
+    ///     let lua = Lua::new();
+    ///     let val = lua.load(r#"{name = "John Smith", age = 20}"#).eval()?;
+    ///     let u: User = lua.from_value(val)?;
+    ///
+    ///     assert_eq!(u, User { name: "John Smith".into(), age: 20 });
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    fn from_value<T: Deserialize<'lua>>(&'lua self, value: Value<'lua>) -> Result<T>;
+}
+
+impl<'lua> LuaSerdeExt<'lua> for Lua {
+    fn null(&'lua self) -> Result<Value<'lua>> {
+        unsafe {
+            let _sg = StackGuard::new(self.state);
+            assert_stack(self.state, 3);
+
+            unsafe extern "C" fn push_null(state: *mut ffi::lua_State) -> c_int {
+                ffi::lua_pushlightuserdata(state, ptr::null_mut());
+                1
+            }
+            protect_lua(self.state, 0, push_null)?;
+            Ok(self.pop_value())
+        }
+    }
+
+    fn array_metatable(&'lua self) -> Result<Table<'lua>> {
+        unsafe {
+            let _sg = StackGuard::new(self.state);
+            assert_stack(self.state, 3);
+
+            unsafe extern "C" fn get_array_mt(state: *mut ffi::lua_State) -> c_int {
+                push_array_metatable(state);
+                1
+            }
+            protect_lua(self.state, 0, get_array_mt)?;
+            Ok(Table(self.pop_ref()))
+        }
+    }
+
+    fn to_value<T>(&'lua self, t: &T) -> Result<Value<'lua>>
+    where
+        T: Serialize + ?Sized,
+    {
+        t.serialize(ser::Serializer(self))
+    }
+
+    fn from_value<T>(&'lua self, value: Value<'lua>) -> Result<T>
+    where
+        T: Deserialize<'lua>,
+    {
+        T::deserialize(de::Deserializer(value))
+    }
+}
+
+pub(crate) unsafe fn init_metatables(state: *mut ffi::lua_State) {
+    ffi::lua_pushlightuserdata(
+        state,
+        &ARRAY_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void,
+    );
+    ffi::lua_newtable(state);
+
+    ffi::lua_pushstring(state, cstr!("__metatable"));
+    ffi::lua_pushboolean(state, 0);
+    ffi::lua_rawset(state, -3);
+
+    ffi::lua_rawset(state, ffi::LUA_REGISTRYINDEX);
+}
+
+pub(crate) unsafe fn push_array_metatable(state: *mut ffi::lua_State) {
+    let key = &ARRAY_METATABLE_REGISTRY_KEY as *const u8 as *mut c_void;
+    ffi::lua_rawgetp(state, ffi::LUA_REGISTRYINDEX, key);
+}
+
+static ARRAY_METATABLE_REGISTRY_KEY: u8 = 0;
+
+pub mod de;
+pub mod ser;

src/serde/ser.rs

@@ -0,0 +1,377 @@
+use std::os::raw::c_int;
+
+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, Number};
+use crate::util::{assert_stack, protect_lua, StackGuard};
+use crate::value::Value;
+
+/// A struct for serializing Rust values into Lua values.
+pub struct Serializer<'lua>(pub &'lua Lua);
+
+macro_rules! lua_serialize_integer {
+    ($name:ident, $t:ty) => {
+        #[inline]
+        fn $name(self, value: $t) -> Result<Value<'lua>> {
+            Ok(Value::Integer(value as Integer))
+        }
+    };
+}
+
+impl<'lua> ser::Serializer for Serializer<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    // Associated types for keeping track of additional state while serializing
+    // compound data structures like sequences and maps.
+    type SerializeSeq = SerializeVec<'lua>;
+    type SerializeTuple = SerializeVec<'lua>;
+    type SerializeTupleStruct = SerializeVec<'lua>;
+    type SerializeTupleVariant = SerializeTupleVariant<'lua>;
+    type SerializeMap = SerializeMap<'lua>;
+    type SerializeStruct = SerializeMap<'lua>;
+    type SerializeStructVariant = SerializeStructVariant<'lua>;
+
+    #[inline]
+    fn serialize_bool(self, value: bool) -> Result<Value<'lua>> {
+        Ok(Value::Boolean(value))
+    }
+
+    lua_serialize_integer!(serialize_i8, i8);
+    lua_serialize_integer!(serialize_u8, u8);
+    lua_serialize_integer!(serialize_i16, i16);
+    lua_serialize_integer!(serialize_u16, u16);
+    lua_serialize_integer!(serialize_i32, i32);
+    lua_serialize_integer!(serialize_u32, u32);
+    lua_serialize_integer!(serialize_u64, u64);
+
+    #[inline]
+    fn serialize_i64(self, value: i64) -> Result<Value<'lua>> {
+        Ok(Value::Integer(value))
+    }
+
+    #[inline]
+    fn serialize_f32(self, value: f32) -> Result<Value<'lua>> {
+        Ok(Value::Number(value as Number))
+    }
+
+    #[inline]
+    fn serialize_f64(self, value: f64) -> Result<Value<'lua>> {
+        Ok(Value::Number(value))
+    }
+
+    #[inline]
+    fn serialize_char(self, value: char) -> Result<Value<'lua>> {
+        self.serialize_str(&value.to_string())
+    }
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<Value<'lua>> {
+        self.0.create_string(value).map(Value::String)
+    }
+
+    #[inline]
+    fn serialize_bytes(self, value: &[u8]) -> Result<Value<'lua>> {
+        self.0.create_string(value).map(Value::String)
+    }
+
+    #[inline]
+    fn serialize_none(self) -> Result<Value<'lua>> {
+        self.0.null()
+    }
+
+    #[inline]
+    fn serialize_some<T>(self, value: &T) -> Result<Value<'lua>>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    #[inline]
+    fn serialize_unit(self) -> Result<Value<'lua>> {
+        self.0.null()
+    }
+
+    #[inline]
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Value<'lua>> {
+        self.0.null()
+    }
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<Value<'lua>> {
+        self.serialize_str(variant)
+    }
+
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<Value<'lua>>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    #[inline]
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        value: &T,
+    ) -> Result<Value<'lua>>
+    where
+        T: ?Sized + Serialize,
+    {
+        let table = self.0.create_table()?;
+        let variant = self.0.create_string(variant)?;
+        let value = self.0.to_value(value)?;
+        table.raw_set(variant, value)?;
+        Ok(Value::Table(table))
+    }
+
+    #[inline]
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
+        let len = len.unwrap_or(0) as c_int;
+        let table = self.0.create_table_with_capacity(len, 0)?;
+        table.set_metatable(Some(self.0.array_metatable()?));
+        Ok(SerializeVec { table })
+    }
+
+    #[inline]
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {
+        self.serialize_seq(Some(len))
+    }
+
+    #[inline]
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        self.serialize_seq(Some(len))
+    }
+
+    #[inline]
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        let name = self.0.create_string(variant)?;
+        let table = self.0.create_table()?;
+        Ok(SerializeTupleVariant { name, table })
+    }
+
+    #[inline]
+    fn serialize_map(self, len: Option<usize>) -> Result<Self::SerializeMap> {
+        let len = len.unwrap_or(0) as c_int;
+        Ok(SerializeMap {
+            key: None,
+            table: self.0.create_table_with_capacity(0, len)?,
+        })
+    }
+
+    #[inline]
+    fn serialize_struct(self, _name: &'static str, len: usize) -> Result<Self::SerializeStruct> {
+        self.serialize_map(Some(len))
+    }
+
+    #[inline]
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        let name = self.0.create_string(variant)?;
+        let table = self.0.create_table_with_capacity(0, len as c_int)?;
+        Ok(SerializeStructVariant { name, table })
+    }
+}
+
+pub struct SerializeVec<'lua> {
+    table: Table<'lua>,
+}
+
+impl<'lua> ser::SerializeSeq for SerializeVec<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        let lua = self.table.0.lua;
+        let value = lua.to_value(value)?;
+        unsafe {
+            let _sg = StackGuard::new(lua.state);
+            assert_stack(lua.state, 4);
+
+            lua.push_ref(&self.table.0);
+            lua.push_value(value)?;
+
+            unsafe extern "C" fn push_to_table(state: *mut ffi::lua_State) -> c_int {
+                let len = ffi::lua_rawlen(state, -2) as Integer;
+                ffi::lua_rawseti(state, -2, len + 1);
+                1
+            }
+
+            protect_lua(lua.state, 2, push_to_table)
+        }
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        Ok(Value::Table(self.table))
+    }
+}
+
+impl<'lua> ser::SerializeTuple for SerializeVec<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl<'lua> ser::SerializeTupleStruct for SerializeVec<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+pub struct SerializeTupleVariant<'lua> {
+    name: String<'lua>,
+    table: Table<'lua>,
+}
+
+impl<'lua> ser::SerializeTupleVariant for SerializeTupleVariant<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        let lua = self.table.0.lua;
+        let idx = self.table.raw_len() + 1;
+        self.table.raw_insert(idx, lua.to_value(value)?)
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        let lua = self.table.0.lua;
+        let table = lua.create_table()?;
+        table.raw_set(self.name, self.table)?;
+        Ok(Value::Table(table))
+    }
+}
+
+pub struct SerializeMap<'lua> {
+    table: Table<'lua>,
+    key: Option<Value<'lua>>,
+}
+
+impl<'lua> ser::SerializeMap for SerializeMap<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        let lua = self.table.0.lua;
+        self.key = Some(lua.to_value(key)?);
+        Ok(())
+    }
+
+    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        let lua = self.table.0.lua;
+        let key = mlua_expect!(
+            self.key.take(),
+            "serialize_value called before serialize_key"
+        );
+        let value = lua.to_value(value)?;
+        self.table.raw_set(key, value)
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        Ok(Value::Table(self.table))
+    }
+}
+
+impl<'lua> ser::SerializeStruct for SerializeMap<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        ser::SerializeMap::serialize_key(self, key)?;
+        ser::SerializeMap::serialize_value(self, value)
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        ser::SerializeMap::end(self)
+    }
+}
+
+pub struct SerializeStructVariant<'lua> {
+    name: String<'lua>,
+    table: Table<'lua>,
+}
+
+impl<'lua> ser::SerializeStructVariant for SerializeStructVariant<'lua> {
+    type Ok = Value<'lua>;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        let lua = self.table.0.lua;
+        self.table.raw_set(key, lua.to_value(value)?)?;
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value<'lua>> {
+        let lua = self.table.0.lua;
+        let table = lua.create_table()?;
+        table.raw_set(self.name, self.table)?;
+        Ok(Value::Table(table))
+    }
+}

src/stdlib.rs

@@ -47,6 +47,8 @@ impl StdLib {
     /// (unsafe) [`debug`](https://www.lua.org/manual/5.3/manual.html#6.10) library
     pub const DEBUG: StdLib = StdLib(1 << 31);
 
+    /// No libraries
+    pub const NONE: StdLib = StdLib(0);
     /// (unsafe) All standard libraries
     pub const ALL: StdLib = StdLib(u32::MAX);
     /// The safe subset of the standard libraries

src/string.rs

@@ -1,5 +1,11 @@
 use std::{slice, str};
 
+#[cfg(feature = "serialize")]
+use {
+    serde::ser::{Serialize, Serializer},
+    std::result::Result as StdResult,
+};
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::types::LuaRef;
@@ -105,3 +111,16 @@ where
         self.as_bytes() == other.as_ref()
     }
 }
+
+#[cfg(feature = "serialize")]
+impl<'lua> Serialize for String<'lua> {
+    fn serialize<S>(&self, serializer: S) -> StdResult<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self.to_str() {
+            Ok(s) => serializer.serialize_str(s),
+            Err(_) => serializer.serialize_bytes(self.as_bytes()),
+        }
+    }
+}

src/table.rs

@@ -1,6 +1,12 @@
 use std::marker::PhantomData;
 use std::os::raw::c_int;
 
+#[cfg(feature = "serialize")]
+use {
+    serde::ser::{Serialize, SerializeMap, SerializeSeq, Serializer},
+    std::result::Result as StdResult,
+};
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
@@ -447,9 +453,53 @@ impl<'lua> Table<'lua> {
         TableSequence {
             table: self.0,
             index: Some(1),
+            len: None,
+            raw: false,
             _phantom: PhantomData,
         }
     }
+
+    /// Consume this table and return an iterator over all values in the sequence part of the table.
+    ///
+    /// Unlike the `sequence_values`, does not invoke `__index` metamethod when iterating.
+    ///
+    /// [`sequence_values`]: #method.sequence_values
+    pub fn raw_sequence_values<V: FromLua<'lua>>(self) -> TableSequence<'lua, V> {
+        TableSequence {
+            table: self.0,
+            index: Some(1),
+            len: None,
+            raw: true,
+            _phantom: PhantomData,
+        }
+    }
+
+    #[cfg(feature = "serialize")]
+    pub(crate) fn raw_sequence_values_by_len<V: FromLua<'lua>>(self) -> TableSequence<'lua, V> {
+        let len = self.raw_len();
+        TableSequence {
+            table: self.0,
+            index: Some(1),
+            len: Some(len),
+            raw: true,
+            _phantom: PhantomData,
+        }
+    }
+
+    #[cfg(feature = "serialize")]
+    pub(crate) fn is_array(&self) -> bool {
+        let lua = self.0.lua;
+        unsafe {
+            let _sg = StackGuard::new(lua.state);
+            assert_stack(lua.state, 3);
+            lua.push_ref(&self.0);
+            if ffi::lua_getmetatable(lua.state, -1) == 0 {
+                return false;
+            }
+            crate::serde::push_array_metatable(lua.state);
+            ffi::lua_rawequal(lua.state, -1, -2) != 0
+        }
+    }
 }
 
 impl<'lua> PartialEq for Table<'lua> {
@@ -500,6 +550,7 @@ pub trait TableExt<'lua> {
     ///
     /// This might invoke the `__index` metamethod.
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     fn call_async_method<'fut, K, A, R>(&self, key: K, args: A) -> LocalBoxFuture<'fut, Result<R>>
     where
         'lua: 'fut,
@@ -514,6 +565,7 @@ pub trait TableExt<'lua> {
     ///
     /// This might invoke the `__index` metamethod.
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     fn call_async_function<'fut, K, A, R>(
         &self,
         key: K,
@@ -580,6 +632,31 @@ impl<'lua> TableExt<'lua> for Table<'lua> {
     }
 }
 
+#[cfg(feature = "serialize")]
+impl<'lua> Serialize for Table<'lua> {
+    fn serialize<S>(&self, serializer: S) -> StdResult<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let len = self.raw_len() as usize;
+        if len > 0 || self.is_array() {
+            let mut seq = serializer.serialize_seq(Some(len))?;
+            for v in self.clone().raw_sequence_values_by_len::<Value>() {
+                let v = v.map_err(serde::ser::Error::custom)?;
+                seq.serialize_element(&v)?;
+            }
+            return seq.end();
+        }
+
+        let mut map = serializer.serialize_map(None)?;
+        for kv in self.clone().pairs::<Value, Value>() {
+            let (k, v) = kv.map_err(serde::ser::Error::custom)?;
+            map.serialize_entry(&k, &v)?;
+        }
+        map.end()
+    }
+}
+
 /// An iterator over the pairs of a Lua table.
 ///
 /// This struct is created by the [`Table::pairs`] method.
@@ -651,6 +728,8 @@ where
 pub struct TableSequence<'lua, V> {
     table: LuaRef<'lua>,
     index: Option<Integer>,
+    len: Option<Integer>,
+    raw: bool,
     _phantom: PhantomData<V>,
 }
 
@@ -669,9 +748,13 @@ where
                 assert_stack(lua.state, 5);
 
                 lua.push_ref(&self.table);
-                match protect_lua_closure(lua.state, 1, 1, |state| ffi::lua_geti(state, -1, index))
-                {
-                    Ok(ffi::LUA_TNIL) => None,
+                let lua_geti = if self.raw {
+                    ffi::lua_rawgeti
+                } else {
+                    ffi::lua_geti
+                };
+                match protect_lua_closure(lua.state, 1, 1, |state| lua_geti(state, -1, index)) {
+                    Ok(ffi::LUA_TNIL) if index > self.len.unwrap_or(0) => None,
                     Ok(_) => {
                         let value = lua.pop_value();
                         self.index = Some(index + 1);

src/thread.rs

@@ -52,6 +52,7 @@ pub struct Thread<'lua>(pub(crate) LuaRef<'lua>);
 /// [`Future`]: ../futures_core/future/trait.Future.html
 /// [`Stream`]: ../futures_core/stream/trait.Stream.html
 #[cfg(feature = "async")]
+#[cfg_attr(docsrs, doc(cfg(feature = "async")))]
 #[derive(Debug)]
 pub struct AsyncThread<'lua, R> {
     thread: Thread<'lua>,
@@ -218,6 +219,7 @@ impl<'lua> Thread<'lua> {
     /// # }
     /// ```
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     pub fn into_async<A, R>(self, args: A) -> AsyncThread<'lua, R>
     where
         A: ToLuaMulti<'lua>,

src/types.rs

@@ -10,6 +10,7 @@ use crate::error::Result;
 use crate::ffi;
 use crate::hook::Debug;
 use crate::lua::Lua;
+use crate::userdata::UserDataWrapped;
 use crate::util::{assert_stack, StackGuard};
 use crate::value::MultiValue;
 
@@ -31,6 +32,8 @@ pub(crate) type AsyncCallback<'lua, 'a> =
 
 pub(crate) type HookCallback = Arc<RefCell<dyn FnMut(&Lua, Debug) -> Result<()>>>;
 
+pub(crate) type UserDataCell<T> = RefCell<UserDataWrapped<T>>;
+
 #[cfg(feature = "send")]
 pub trait MaybeSend: Send {}
 #[cfg(feature = "send")]

src/userdata.rs

@@ -1,15 +1,21 @@
-use std::cell::{Ref, RefCell, RefMut};
+use std::cell::{Ref, RefMut};
 
 #[cfg(feature = "async")]
 use std::future::Future;
 
+#[cfg(feature = "serialize")]
+use {
+    serde::ser::{self, Serialize, Serializer},
+    std::result::Result as StdResult,
+};
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
 use crate::lua::Lua;
 use crate::table::Table;
-use crate::types::{LuaRef, MaybeSend};
-use crate::util::{assert_stack, get_userdata, StackGuard};
+use crate::types::{LuaRef, MaybeSend, UserDataCell};
+use crate::util::{assert_stack, get_destructed_userdata_metatable, get_userdata, StackGuard};
 use crate::value::{FromLua, FromLuaMulti, ToLua, ToLuaMulti, Value};
 
 /// Kinds of metamethods that can be overridden.
@@ -185,6 +191,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
     ///
     /// [`add_method`]: #method.add_method
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     fn add_async_method<S, A, R, M, MR>(&mut self, name: &S, method: M)
     where
         T: Clone,
@@ -231,6 +238,7 @@ pub trait UserDataMethods<'lua, T: UserData> {
     ///
     /// [`add_function`]: #method.add_function
     #[cfg(feature = "async")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
     fn add_async_function<S, A, R, F, FR>(&mut self, name: &S, function: F)
     where
         T: Clone,
@@ -360,6 +368,71 @@ pub trait UserData: Sized {
     fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(_methods: &mut M) {}
 }
 
+pub(crate) struct UserDataWrapped<T> {
+    pub(crate) data: *mut T,
+    #[cfg(feature = "serialize")]
+    ser: *mut dyn erased_serde::Serialize,
+}
+
+impl<T> Drop for UserDataWrapped<T> {
+    fn drop(&mut self) {
+        unsafe {
+            drop(Box::from_raw(self.data));
+            #[cfg(feature = "serialize")]
+            if self.data as *mut () != self.ser as *mut () {
+                drop(Box::from_raw(self.ser));
+            }
+        }
+    }
+}
+
+impl<T> UserDataWrapped<T> {
+    pub(crate) fn new(data: T) -> Self {
+        UserDataWrapped {
+            data: Box::into_raw(Box::new(data)),
+            #[cfg(feature = "serialize")]
+            ser: Box::into_raw(Box::new(UserDataSerializeError)),
+        }
+    }
+
+    #[cfg(feature = "serialize")]
+    pub(crate) fn new_ser(data: T) -> Self
+    where
+        T: 'static + Serialize,
+    {
+        let data_raw = Box::into_raw(Box::new(data));
+        UserDataWrapped {
+            data: data_raw,
+            ser: data_raw,
+        }
+    }
+}
+
+impl<T> AsRef<T> for UserDataWrapped<T> {
+    fn as_ref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T> AsMut<T> for UserDataWrapped<T> {
+    fn as_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data }
+    }
+}
+
+#[cfg(feature = "serialize")]
+pub(crate) struct UserDataSerializeError;
+
+#[cfg(feature = "serialize")]
+impl Serialize for UserDataSerializeError {
+    fn serialize<S>(&self, _serializer: S) -> StdResult<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        Err(ser::Error::custom("cannot serialize <userdata>"))
+    }
+}
+
 /// Handle to an internal Lua userdata for any type that implements [`UserData`].
 ///
 /// Similar to `std::any::Any`, this provides an interface for dynamic type checking via the [`is`]
@@ -382,7 +455,7 @@ pub struct AnyUserData<'lua>(pub(crate) LuaRef<'lua>);
 impl<'lua> AnyUserData<'lua> {
     /// Checks whether the type of this userdata is `T`.
     pub fn is<T: 'static + UserData>(&self) -> bool {
-        match self.inspect(|_: &RefCell<T>| Ok(())) {
+        match self.inspect(|_: &UserDataCell<T>| Ok(())) {
             Ok(()) => true,
             Err(Error::UserDataTypeMismatch) => false,
             Err(_) => unreachable!(),
@@ -396,7 +469,10 @@ impl<'lua> AnyUserData<'lua> {
     /// Returns a `UserDataBorrowError` if the userdata is already mutably borrowed. Returns a
     /// `UserDataTypeMismatch` if the userdata is not of type `T`.
     pub fn borrow<T: 'static + UserData>(&self) -> Result<Ref<T>> {
-        self.inspect(|cell| Ok(cell.try_borrow().map_err(|_| Error::UserDataBorrowError)?))
+        self.inspect(|cell| {
+            let cell_ref = cell.try_borrow().map_err(|_| Error::UserDataBorrowError)?;
+            Ok(Ref::map(cell_ref, |x| unsafe { &*x.data }))
+        })
     }
 
     /// Borrow this userdata mutably if it is of type `T`.
@@ -407,9 +483,10 @@ impl<'lua> AnyUserData<'lua> {
     /// `UserDataTypeMismatch` if the userdata is not of type `T`.
     pub fn borrow_mut<T: 'static + UserData>(&self) -> Result<RefMut<T>> {
         self.inspect(|cell| {
-            Ok(cell
+            let cell_ref = cell
                 .try_borrow_mut()
-                .map_err(|_| Error::UserDataBorrowMutError)?)
+                .map_err(|_| Error::UserDataBorrowMutError)?;
+            Ok(RefMut::map(cell_ref, |x| unsafe { &mut *x.data }))
         })
     }
 
@@ -515,7 +592,7 @@ impl<'lua> AnyUserData<'lua> {
     fn inspect<'a, T, R, F>(&'a self, func: F) -> Result<R>
     where
         T: 'static + UserData,
-        F: FnOnce(&'a RefCell<T>) -> Result<R>,
+        F: FnOnce(&'a UserDataCell<T>) -> Result<R>,
     {
         unsafe {
             let lua = self.0.lua;
@@ -534,9 +611,16 @@ impl<'lua> AnyUserData<'lua> {
                 );
 
                 if ffi::lua_rawequal(lua.state, -1, -2) == 0 {
-                    Err(Error::UserDataTypeMismatch)
+                    // Maybe UserData destructed?
+                    ffi::lua_pop(lua.state, 1);
+                    get_destructed_userdata_metatable(lua.state);
+                    if ffi::lua_rawequal(lua.state, -1, -2) == 1 {
+                        Err(Error::UserDataDestructed)
+                    } else {
+                        Err(Error::UserDataTypeMismatch)
+                    }
                 } else {
-                    func(&*get_userdata::<RefCell<T>>(lua.state, -3))
+                    func(&*get_userdata::<UserDataCell<T>>(lua.state, -3))
                 }
             }
         }
@@ -555,3 +639,24 @@ impl<'lua> AsRef<AnyUserData<'lua>> for AnyUserData<'lua> {
         self
     }
 }
+
+#[cfg(feature = "serialize")]
+impl<'lua> Serialize for AnyUserData<'lua> {
+    fn serialize<S>(&self, serializer: S) -> StdResult<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let f = || unsafe {
+            let lua = self.0.lua;
+            let _sg = StackGuard::new(lua.state);
+            assert_stack(lua.state, 2);
+
+            lua.push_userdata_ref(&self.0)?;
+            let ud = &*get_userdata::<UserDataCell<()>>(lua.state, -1);
+            (*ud.try_borrow().map_err(|_| Error::UserDataBorrowError)?.ser)
+                .serialize(serializer)
+                .map_err(|err| Error::SerializeError(err.to_string()))
+        };
+        f().map_err(ser::Error::custom)
+    }
+}

src/util.rs

@@ -759,7 +759,7 @@ unsafe fn to_string<'a>(state: *mut ffi::lua_State, index: c_int) -> Cow<'a, str
     }
 }
 
-unsafe fn get_destructed_userdata_metatable(state: *mut ffi::lua_State) {
+pub(crate) unsafe fn get_destructed_userdata_metatable(state: *mut ffi::lua_State) {
     ffi::lua_pushlightuserdata(
         state,
         &DESTRUCTED_USERDATA_METATABLE as *const u8 as *mut c_void,

src/value.rs

@@ -1,6 +1,12 @@
 use std::iter::{self, FromIterator};
 use std::{slice, str, vec};
 
+#[cfg(feature = "serialize")]
+use {
+    serde::ser::{self, Serialize, Serializer},
+    std::result::Result as StdResult,
+};
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
@@ -110,6 +116,29 @@ impl<'lua> AsRef<Value<'lua>> for Value<'lua> {
     }
 }
 
+#[cfg(feature = "serialize")]
+impl<'lua> Serialize for Value<'lua> {
+    fn serialize<S>(&self, serializer: S) -> StdResult<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self {
+            Value::Nil => serializer.serialize_unit(),
+            Value::Boolean(b) => serializer.serialize_bool(*b),
+            Value::Integer(i) => serializer.serialize_i64(*i),
+            Value::Number(n) => serializer.serialize_f64(*n),
+            Value::String(s) => s.serialize(serializer),
+            Value::Table(t) => t.serialize(serializer),
+            Value::UserData(ud) => ud.serialize(serializer),
+            Value::LightUserData(ud) if ud.0.is_null() => serializer.serialize_none(),
+            Value::Error(_) | Value::LightUserData(_) | Value::Function(_) | Value::Thread(_) => {
+                let msg = format!("cannot serialize <{}>", self.type_name());
+                Err(ser::Error::custom(msg))
+            }
+        }
+    }
+}
+
 /// Trait for types convertible to `Value`.
 pub trait ToLua<'lua> {
     /// Performs the conversion.

tests/compile/async_nonstatic_userdata.stderr

@@ -22,14 +22,14 @@ note: ...so that the types are compatible
 13 | |                 Ok(())
 14 | |             });
    | |_____________^
-   = note: expected  `main::MyUserData<'_>`
-              found  `main::MyUserData<'a>`
+   = note: expected `(MyUserData<'_>,)`
+              found `(MyUserData<'a>,)`
 note: but, the lifetime must be valid for the lifetime `'lua` as defined on the method body at 10:24...
   --> $DIR/async_nonstatic_userdata.rs:10:24
    |
 10 |         fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
    |                        ^^^^
-note: ...so that the type `impl std::future::Future` will meet its required lifetime bounds
+note: ...so that the type `impl Future` will meet its required lifetime bounds
   --> $DIR/async_nonstatic_userdata.rs:11:21
    |
 11 |             methods.add_async_method("print", |_, data, ()| async move {

tests/compile/lua_norefunwindsafe.stderr

@@ -1,11 +1,16 @@
-error[E0277]: the type `std::cell::UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+error[E0277]: the type `UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
    --> $DIR/lua_norefunwindsafe.rs:7:5
     |
 7   |     catch_unwind(|| lua.create_table().unwrap());
-    |     ^^^^^^^^^^^^ `std::cell::UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+    |     ^^^^^^^^^^^^ `UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
     |
-    = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<()>`
-    = note: required because it appears within the type `std::marker::PhantomData<std::cell::UnsafeCell<()>>`
-    = note: required because it appears within the type `mlua::lua::Lua`
-    = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
-    = note: required because it appears within the type `[closure@$DIR/tests/compile/lua_norefunwindsafe.rs:7:18: 7:48 lua:&mlua::lua::Lua]`
+   ::: $RUST/std/src/panic.rs
+    |
+    | pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
+    |                                        ---------- required by this bound in `catch_unwind`
+    |
+    = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<()>`
+    = note: required because it appears within the type `PhantomData<UnsafeCell<()>>`
+    = note: required because it appears within the type `Lua`
+    = note: required because of the requirements on the impl of `UnwindSafe` for `&Lua`
+    = note: required because it appears within the type `[closure@$DIR/tests/compile/lua_norefunwindsafe.rs:7:18: 7:48]`

tests/compile/non_send.stderr

@@ -1,14 +1,14 @@
-error[E0277]: `std::rc::Rc<std::cell::Cell<i32>>` cannot be sent between threads safely
+error[E0277]: `Rc<Cell<i32>>` cannot be sent between threads safely
   --> $DIR/non_send.rs:11:9
    |
 11 |       lua.create_function(move |_, ()| {
    |  _________^^^^^^^^^^^^^^^_-
    | |         |
-   | |         `std::rc::Rc<std::cell::Cell<i32>>` cannot be sent between threads safely
+   | |         `Rc<Cell<i32>>` cannot be sent between threads safely
 12 | |         Ok(data.get())
 13 | |     })?
-   | |_____- within this `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6 data:std::rc::Rc<std::cell::Cell<i32>>]`
+   | |_____- 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 data:std::rc::Rc<std::cell::Cell<i32>>]`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<std::cell::Cell<i32>>`
-   = note: required because it appears within the type `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6 data:std::rc::Rc<std::cell::Cell<i32>>]`
-   = note: required because of the requirements on the impl of `mlua::types::MaybeSend` for `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6 data:std::rc::Rc<std::cell::Cell<i32>>]`
+   = help: within `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`, the trait `Send` is not implemented for `Rc<Cell<i32>>`
+   = note: required because it appears within the type `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`
+   = 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/ref_nounwindsafe.stderr

@@ -1,13 +1,18 @@
-error[E0277]: the type `std::cell::UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+error[E0277]: the type `UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
    --> $DIR/ref_nounwindsafe.rs:8:5
     |
 8   |     catch_unwind(move || table.set("a", "b").unwrap());
-    |     ^^^^^^^^^^^^ `std::cell::UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
+    |     ^^^^^^^^^^^^ `UnsafeCell<()>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
     |
-    = help: within `mlua::lua::Lua`, the trait `std::panic::RefUnwindSafe` is not implemented for `std::cell::UnsafeCell<()>`
-    = note: required because it appears within the type `std::marker::PhantomData<std::cell::UnsafeCell<()>>`
-    = note: required because it appears within the type `mlua::lua::Lua`
-    = note: required because of the requirements on the impl of `std::panic::UnwindSafe` for `&mlua::lua::Lua`
+   ::: $RUST/std/src/panic.rs
+    |
+    | pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
+    |                                        ---------- required by this bound in `catch_unwind`
+    |
+    = help: within `Lua`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<()>`
+    = note: required because it appears within the type `PhantomData<UnsafeCell<()>>`
+    = note: required because it appears within the type `Lua`
+    = note: required because of the requirements on the impl of `UnwindSafe` for `&Lua`
     = note: required because it appears within the type `mlua::types::LuaRef<'_>`
-    = note: required because it appears within the type `mlua::table::Table<'_>`
-    = note: required because it appears within the type `[closure@$DIR/tests/compile/ref_nounwindsafe.rs:8:18: 8:54 table:mlua::table::Table<'_>]`
+    = note: required because it appears within the type `LuaTable<'_>`
+    = note: required because it appears within the type `[closure@$DIR/tests/compile/ref_nounwindsafe.rs:8:18: 8:54]`

tests/compile/scope_callback_capture.stderr

@@ -1,45 +1,26 @@
-error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
-  --> $DIR/scope_callback_capture.rs:8:14
-   |
-8  |             .create_function_mut(move |_, t: Table| {
-   |              ^^^^^^^^^^^^^^^^^^^
-   |
-note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the body at 5:15...
-  --> $DIR/scope_callback_capture.rs:5:15
-   |
-5  |       lua.scope(|scope| {
-   |  _______________^
-6  | |         let mut inner: Option<Table> = None;
-7  | |         let f = scope
-8  | |             .create_function_mut(move |_, t: Table| {
-...  |
-16 | |         Ok(())
-17 | |     });
-   | |_____^
-note: ...so that reference does not outlive borrowed content
+warning: unused variable: `old`
+ --> $DIR/scope_callback_capture.rs:9:29
+  |
+9 |                 if let Some(old) = inner.take() {
+  |                             ^^^ help: if this is intentional, prefix it with an underscore: `_old`
+  |
+  = note: `#[warn(unused_variables)]` on by default
+
+error[E0521]: borrowed data escapes outside of closure
   --> $DIR/scope_callback_capture.rs:7:17
    |
-7  |         let f = scope
-   |                 ^^^^^
-note: but, the lifetime must be valid for the method call at 5:5...
-  --> $DIR/scope_callback_capture.rs:5:5
-   |
-5  | /     lua.scope(|scope| {
-6  | |         let mut inner: Option<Table> = None;
-7  | |         let f = scope
+5  |       lua.scope(|scope| {
+   |                  -----
+   |                  |
+   |                  `scope` declared here, outside of the closure body
+   |                  `scope` is a reference that is only valid in the closure body
+6  |           let mut inner: Option<Table> = None;
+7  |           let f = scope
+   |  _________________^
 8  | |             .create_function_mut(move |_, t: Table| {
+9  | |                 if let Some(old) = inner.take() {
+10 | |                     // Access old callback `Lua`.
 ...  |
-16 | |         Ok(())
-17 | |     });
-   | |______^
-note: ...so that a type/lifetime parameter is in scope here
-  --> $DIR/scope_callback_capture.rs:5:5
-   |
-5  | /     lua.scope(|scope| {
-6  | |         let mut inner: Option<Table> = None;
-7  | |         let f = scope
-8  | |             .create_function_mut(move |_, t: Table| {
-...  |
-16 | |         Ok(())
-17 | |     });
-   | |______^
+13 | |                 Ok(())
+14 | |             })?;
+   | |______________^ `scope` escapes the closure body here

tests/compile/scope_callback_inner.stderr

@@ -1,45 +1,42 @@
-error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
-  --> $DIR/scope_callback_inner.rs:8:14
-   |
-8  |             .create_function_mut(|_, t: Table| {
-   |              ^^^^^^^^^^^^^^^^^^^
-   |
-note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the body at 5:15...
-  --> $DIR/scope_callback_inner.rs:5:15
-   |
-5  |       lua.scope(|scope| {
-   |  _______________^
-6  | |         let mut inner: Option<Table> = None;
-7  | |         let f = scope
-8  | |             .create_function_mut(|_, t: Table| {
-...  |
-13 | |         Ok(())
-14 | |     });
-   | |_____^
-note: ...so that reference does not outlive borrowed content
+error[E0521]: borrowed data escapes outside of closure
   --> $DIR/scope_callback_inner.rs:7:17
    |
-7  |         let f = scope
-   |                 ^^^^^
-note: but, the lifetime must be valid for the method call at 5:5...
-  --> $DIR/scope_callback_inner.rs:5:5
-   |
-5  | /     lua.scope(|scope| {
-6  | |         let mut inner: Option<Table> = None;
-7  | |         let f = scope
+5  |       lua.scope(|scope| {
+   |                  -----
+   |                  |
+   |                  `scope` declared here, outside of the closure body
+   |                  `scope` is a reference that is only valid in the closure body
+6  |           let mut inner: Option<Table> = None;
+7  |           let f = scope
+   |  _________________^
 8  | |             .create_function_mut(|_, t: Table| {
-...  |
-13 | |         Ok(())
-14 | |     });
-   | |______^
-note: ...so that a type/lifetime parameter is in scope here
-  --> $DIR/scope_callback_inner.rs:5:5
+9  | |                 inner = Some(t);
+10 | |                 Ok(())
+11 | |             })?;
+   | |______________^ `scope` escapes the closure body here
+
+error[E0373]: closure may outlive the current function, but it borrows `inner`, which is owned by the current function
+  --> $DIR/scope_callback_inner.rs:8:34
    |
-5  | /     lua.scope(|scope| {
-6  | |         let mut inner: Option<Table> = None;
-7  | |         let f = scope
+5  |     lua.scope(|scope| {
+   |                ----- has type `&Scope<'_, '2>`
+...
+8  |             .create_function_mut(|_, t: Table| {
+   |                                  ^^^^^^^^^^^^^ may outlive borrowed value `inner`
+9  |                 inner = Some(t);
+   |                 ----- `inner` is borrowed here
+   |
+note: function requires argument type to outlive `'2`
+  --> $DIR/scope_callback_inner.rs:7:17
+   |
+7  |           let f = scope
+   |  _________________^
 8  | |             .create_function_mut(|_, t: Table| {
-...  |
-13 | |         Ok(())
-14 | |     });
-   | |______^
+9  | |                 inner = Some(t);
+10 | |                 Ok(())
+11 | |             })?;
+   | |______________^
+help: to force the closure to take ownership of `inner` (and any other referenced variables), use the `move` keyword
+   |
+8  |             .create_function_mut(move |_, t: Table| {
+   |                                  ^^^^^^^^^^^^^^^^^^

tests/compile/scope_callback_outer.stderr

@@ -1,11 +1,30 @@
-error: borrowed data cannot be stored outside of its closure
- --> $DIR/scope_callback_outer.rs:7:17
-  |
-5 |     let mut outer: Option<Table> = None;
-  |         --------- ...so that variable is valid at time of its declaration
-6 |     lua.scope(|scope| {
-  |               ------- borrowed data cannot outlive this closure
-7 |         let f = scope
-  |                 ^^^^^ cannot be stored outside of its closure
-8 |             .create_function_mut(|_, t: Table| {
-  |              ------------------- cannot infer an appropriate lifetime...
+error[E0521]: borrowed data escapes outside of closure
+  --> $DIR/scope_callback_outer.rs:7:17
+   |
+6  |       lua.scope(|scope| {
+   |                  -----
+   |                  |
+   |                  `scope` declared here, outside of the closure body
+   |                  `scope` is a reference that is only valid in the closure body
+7  |           let f = scope
+   |  _________________^
+8  | |             .create_function_mut(|_, t: Table| {
+9  | |                 outer = Some(t);
+10 | |                 Ok(())
+11 | |             })?;
+   | |______________^ `scope` escapes the closure body here
+
+error[E0597]: `outer` does not live long enough
+  --> $DIR/scope_callback_outer.rs:9:17
+   |
+6  |     lua.scope(|scope| {
+   |               ------- value captured here
+...
+9  |                 outer = Some(t);
+   |                 ^^^^^ borrowed value does not live long enough
+...
+15 | }
+   | -
+   | |
+   | `outer` dropped here while still borrowed
+   | borrow might be used here, when `outer` is dropped and runs the destructor for type `Option<LuaTable<'_>>`

tests/compile/scope_invariance.stderr

@@ -2,7 +2,7 @@ error[E0373]: closure may outlive the current function, but it borrows `test`, w
   --> $DIR/scope_invariance.rs:14:38
    |
 9  |     lua.scope(|scope| {
-   |                ----- has type `&mlua::scope::Scope<'_, '1>`
+   |                ----- has type `&Scope<'_, '1>`
 ...
 14 |                 .create_function_mut(|_, ()| {
    |                                      ^^^^^^^ may outlive borrowed value `test`

tests/compile/scope_userdata_borrow.stderr

@@ -2,7 +2,7 @@ error[E0597]: `ibad` does not live long enough
   --> $DIR/scope_userdata_borrow.rs:15:56
    |
 11 |     lua.scope(|scope| {
-   |                ----- has type `&mlua::scope::Scope<'_, '1>`
+   |                ----- has type `&Scope<'_, '1>`
 ...
 15 |             scope.create_nonstatic_userdata(MyUserData(&ibad)).unwrap();
    |             -------------------------------------------^^^^^--

tests/function.rs

@@ -87,3 +87,17 @@ fn test_rust_function() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_dump() -> Result<()> {
+    let lua = unsafe { Lua::unsafe_new() };
+
+    let concat_lua = lua
+        .load(r#"function(arg1, arg2) return arg1 .. arg2 end"#)
+        .eval::<Function>()?;
+    let concat = lua.load(&concat_lua.dump(false)?).into_function()?;
+
+    assert_eq!(concat.call::<_, String>(("foo", "bar"))?, "foobar");
+
+    Ok(())
+}

tests/serde.rs

@@ -0,0 +1,341 @@
+#![cfg(feature = "serialize")]
+#![cfg_attr(
+    all(feature = "luajit", target_os = "macos", target_arch = "x86_64"),
+    feature(link_args)
+)]
+
+#[cfg_attr(
+    all(feature = "luajit", target_os = "macos", target_arch = "x86_64"),
+    link_args = "-pagezero_size 10000 -image_base 100000000",
+    allow(unused_attributes)
+)]
+extern "system" {}
+
+use mlua::{Error, Lua, LuaSerdeExt, Result as LuaResult, UserData, Value};
+use serde::{Deserialize, Serialize};
+
+#[test]
+fn test_serialize() -> Result<(), Box<dyn std::error::Error>> {
+    #[derive(Serialize)]
+    struct MyUserData(i64, String);
+
+    impl UserData for MyUserData {};
+
+    let lua = Lua::new();
+    let globals = lua.globals();
+
+    let ud = lua.create_ser_userdata(MyUserData(123, "test userdata".into()))?;
+    globals.set("ud", ud)?;
+    globals.set("null", lua.null()?)?;
+
+    let empty_array = lua.create_table()?;
+    empty_array.set_metatable(Some(lua.array_metatable()?));
+    globals.set("empty_array", empty_array)?;
+
+    let val = lua
+        .load(
+            r#"
+        {
+            _bool = true,
+            _integer = 123,
+            _number = 321.99,
+            _string = "test string serialization",
+            _table_arr = {nil, "value 1", nil, "value 2", {}},
+            _table_map = {["table"] = "map", ["null"] = null},
+            _bytes = "\240\040\140\040",
+            _userdata = ud,
+            _null = null,
+            _empty_map = {},
+            _empty_array = empty_array,
+        }
+    "#,
+        )
+        .eval::<Value>()?;
+
+    let json = serde_json::json!({
+        "_bool": true,
+        "_integer": 123,
+        "_number": 321.99,
+        "_string": "test string serialization",
+        "_table_arr": [null, "value 1", null, "value 2", {}],
+        "_table_map": {"table": "map", "null": null},
+        "_bytes": [240, 40, 140, 40],
+        "_userdata": [123, "test userdata"],
+        "_null": null,
+        "_empty_map": {},
+        "_empty_array": [],
+    });
+
+    assert_eq!(serde_json::to_value(&val)?, json);
+
+    // Test to-from loop
+    let val = lua.to_value(&json)?;
+    let expected_json = lua.from_value::<serde_json::Value>(val)?;
+    assert_eq!(expected_json, json);
+
+    Ok(())
+}
+
+#[test]
+fn test_serialize_in_scope() -> LuaResult<()> {
+    #[derive(Serialize, Clone)]
+    struct MyUserData(i64, String);
+
+    impl UserData for MyUserData {};
+
+    let lua = Lua::new();
+    lua.scope(|scope| {
+        let ud = scope.create_ser_userdata(MyUserData(-5, "test userdata".into()))?;
+        assert_eq!(
+            serde_json::to_value(&ud).unwrap(),
+            serde_json::json!((-5, "test userdata"))
+        );
+        Ok(())
+    })?;
+
+    lua.scope(|scope| {
+        let ud = scope.create_ser_userdata(MyUserData(-5, "test userdata".into()))?;
+        lua.globals().set("ud", ud)
+    })?;
+    let val = lua.load("ud").eval::<Value>()?;
+    match serde_json::to_value(&val) {
+        Ok(v) => panic!("expected destructed error, got {}", v),
+        Err(e) if e.to_string().contains("destructed") => {}
+        Err(e) => panic!("expected destructed error, got {}", e),
+    }
+
+    Ok(())
+}
+
+#[test]
+fn test_serialize_failure() -> Result<(), Box<dyn std::error::Error>> {
+    #[derive(Serialize)]
+    struct MyUserData(i64);
+
+    impl UserData for MyUserData {};
+
+    let lua = Lua::new();
+
+    let ud = Value::UserData(lua.create_userdata(MyUserData(123))?);
+    match serde_json::to_value(&ud) {
+        Ok(v) => panic!("expected serialization error, got {}", v),
+        Err(serde_json::Error { .. }) => {}
+    }
+
+    let func = lua.create_function(|_, _: ()| Ok(()))?;
+    match serde_json::to_value(&Value::Function(func.clone())) {
+        Ok(v) => panic!("expected serialization error, got {}", v),
+        Err(serde_json::Error { .. }) => {}
+    }
+
+    let thr = lua.create_thread(func)?;
+    match serde_json::to_value(&Value::Thread(thr)) {
+        Ok(v) => panic!("expected serialization error, got {}", v),
+        Err(serde_json::Error { .. }) => {}
+    }
+
+    Ok(())
+}
+
+#[test]
+fn test_to_value_struct() -> LuaResult<()> {
+    let lua = Lua::new();
+    let globals = lua.globals();
+    globals.set("null", lua.null()?)?;
+
+    #[derive(Serialize)]
+    struct Test {
+        name: String,
+        key: i64,
+        data: Option<bool>,
+    };
+
+    let test = Test {
+        name: "alex".to_string(),
+        key: -16,
+        data: None,
+    };
+
+    globals.set("value", lua.to_value(&test)?)?;
+    lua.load(
+        r#"
+            assert(value["name"] == "alex")
+            assert(value["key"] == -16)
+            assert(value["data"] == null)
+        "#,
+    )
+    .exec()
+}
+
+#[test]
+fn test_to_value_enum() -> LuaResult<()> {
+    let lua = Lua::new();
+    let globals = lua.globals();
+    globals.set("null", lua.null()?)?;
+
+    #[derive(Serialize)]
+    struct Test {
+        name: String,
+        key: i64,
+        data: Option<bool>,
+    };
+
+    let test = Test {
+        name: "alex".to_string(),
+        key: -16,
+        data: None,
+    };
+
+    globals.set("value", lua.to_value(&test)?)?;
+    lua.load(
+        r#"
+            assert(value["name"] == "alex")
+            assert(value["key"] == -16)
+            assert(value["data"] == null)
+        "#,
+    )
+    .exec()?;
+
+    #[derive(Serialize)]
+    enum E {
+        Unit,
+        Integer(u32),
+        Tuple(u32, u32),
+        Struct { a: u32 },
+    }
+
+    let u = E::Unit;
+    globals.set("value", lua.to_value(&u)?)?;
+    lua.load(r#"assert(value == "Unit")"#).exec()?;
+
+    let n = E::Integer(1);
+    globals.set("value", lua.to_value(&n)?)?;
+    lua.load(r#"assert(value["Integer"] == 1)"#).exec()?;
+
+    let t = E::Tuple(1, 2);
+    globals.set("value", lua.to_value(&t)?)?;
+    lua.load(
+        r#"
+            assert(value["Tuple"][1] == 1)
+            assert(value["Tuple"][2] == 2)
+        "#,
+    )
+    .exec()?;
+
+    let s = E::Struct { a: 1 };
+    globals.set("value", lua.to_value(&s)?)?;
+    lua.load(r#"assert(value["Struct"]["a"] == 1)"#).exec()?;
+    Ok(())
+}
+
+#[test]
+fn test_from_value_struct() -> Result<(), Box<dyn std::error::Error>> {
+    let lua = Lua::new();
+
+    #[derive(Deserialize, PartialEq, Debug)]
+    struct Test {
+        int: u32,
+        seq: Vec<String>,
+        map: std::collections::HashMap<i32, i32>,
+        empty: Vec<()>,
+        tuple: (u8, u8, u8),
+    }
+
+    let value = lua
+        .load(
+            r#"
+            {
+                int = 1,
+                seq = {"a", "b"},
+                map = {2, [4] = 1},
+                empty = {},
+                tuple = {10, 20, 30},
+            }
+        "#,
+        )
+        .eval::<Value>()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(
+        Test {
+            int: 1,
+            seq: vec!["a".into(), "b".into()],
+            map: vec![(1, 2), (4, 1)].into_iter().collect(),
+            empty: vec![],
+            tuple: (10, 20, 30),
+        },
+        got
+    );
+
+    Ok(())
+}
+
+#[test]
+fn test_from_value_enum() -> Result<(), Box<dyn std::error::Error>> {
+    let lua = Lua::new();
+
+    #[derive(Deserialize, PartialEq, Debug)]
+    enum E {
+        Unit,
+        Integer(u32),
+        Tuple(u32, u32),
+        Struct { a: u32 },
+    }
+
+    let value = lua.load(r#""Unit""#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(E::Unit, got);
+
+    let value = lua.load(r#"{Integer = 1}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(E::Integer(1), got);
+
+    let value = lua.load(r#"{Tuple = {1, 2}}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(E::Tuple(1, 2), got);
+
+    let value = lua.load(r#"{Struct = {a = 3}}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(E::Struct { a: 3 }, got);
+
+    Ok(())
+}
+
+#[test]
+fn test_from_value_enum_untagged() -> Result<(), Box<dyn std::error::Error>> {
+    let lua = Lua::new();
+    lua.globals().set("null", lua.null()?)?;
+
+    #[derive(Deserialize, PartialEq, Debug)]
+    #[serde(untagged)]
+    enum Eut {
+        Unit,
+        Integer(u64),
+        Tuple(u32, u32),
+        Struct { a: u32 },
+    }
+
+    let value = lua.load(r#"null"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(Eut::Unit, got);
+
+    let value = lua.load(r#"1"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(Eut::Integer(1), got);
+
+    let value = lua.load(r#"{3, 1}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(Eut::Tuple(3, 1), got);
+
+    let value = lua.load(r#"{a = 10}"#).eval()?;
+    let got = lua.from_value(value)?;
+    assert_eq!(Eut::Struct { a: 10 }, got);
+
+    let value = lua.load(r#"{b = 12}"#).eval()?;
+    match lua.from_value::<Eut>(value) {
+        Ok(v) => panic!("expected Error::DeserializeError, got {:?}", v),
+        Err(Error::DeserializeError(_)) => {}
+        Err(e) => panic!("expected Error::DeserializeError, got {}", e),
+    }
+
+    Ok(())
+}

tests/tests.rs

@@ -16,8 +16,8 @@ use std::sync::Arc;
 use std::{error, f32, f64, fmt};
 
 use mlua::{
-    Error, ExternalError, Function, Lua, Nil, Result, StdLib, String, Table, UserData, Value,
-    Variadic,
+    ChunkMode, Error, ExternalError, Function, Lua, Nil, Result, StdLib, String, Table, UserData,
+    Value, Variadic,
 };
 
 #[test]
@@ -56,6 +56,37 @@ fn test_safety() -> Result<()> {
         Ok(_) => panic!("expected RuntimeError, got no error"),
     }
 
+    match lua.load("1 + 1").set_mode(ChunkMode::Binary).exec() {
+        Err(Error::SafetyError(msg)) => {
+            assert!(msg.contains("binary chunks are disabled in safe mode"))
+        }
+        Err(e) => panic!("expected SafetyError, got {:?}", e),
+        Ok(_) => panic!("expected SafetyError, got no error"),
+    }
+
+    let bytecode = lua.load("return 1 + 1").into_function()?.dump(true)?;
+    match lua.load(&bytecode).exec() {
+        Err(Error::SafetyError(msg)) => {
+            assert!(msg.contains("binary chunks are disabled in safe mode"))
+        }
+        Err(e) => panic!("expected SafetyError, got {:?}", e),
+        Ok(_) => panic!("expected SafetyError, got no error"),
+    }
+    drop(lua);
+
+    // Test safety rules after dynamically loading `package` library
+    let lua = Lua::new_with(StdLib::NONE)?;
+    assert!(lua.globals().get::<_, Option<Value>>("require")?.is_none());
+    lua.load_from_std_lib(StdLib::PACKAGE)?;
+    match lua.load(r#"package.loadlib()"#).exec() {
+        Err(Error::CallbackError { ref cause, .. }) => match cause.as_ref() {
+            Error::SafetyError(_) => {}
+            e => panic!("expected SafetyError cause, got {:?}", e),
+        },
+        Err(e) => panic!("expected CallbackError, got {:?}", e),
+        Ok(_) => panic!("expected CallbackError, got no error"),
+    };
+
     Ok(())
 }
 
@@ -127,6 +158,41 @@ fn test_eval() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_load_mode() -> Result<()> {
+    let lua = unsafe { Lua::unsafe_new() };
+
+    assert_eq!(
+        lua.load("1 + 1").set_mode(ChunkMode::Text).eval::<i32>()?,
+        2
+    );
+    match lua.load("1 + 1").set_mode(ChunkMode::Binary).exec() {
+        Ok(_) => panic!("expected SyntaxError, got no error"),
+        Err(Error::SyntaxError { message: msg, .. }) => {
+            assert!(msg.contains("attempt to load a text chunk"))
+        }
+        Err(e) => panic!("expected SyntaxError, got {:?}", e),
+    };
+
+    let bytecode = lua.load("return 1 + 1").into_function()?.dump(true)?;
+    assert_eq!(lua.load(&bytecode).eval::<i32>()?, 2);
+    assert_eq!(
+        lua.load(&bytecode)
+            .set_mode(ChunkMode::Binary)
+            .eval::<i32>()?,
+        2
+    );
+    match lua.load(&bytecode).set_mode(ChunkMode::Text).exec() {
+        Ok(_) => panic!("expected SyntaxError, got no error"),
+        Err(Error::SyntaxError { message: msg, .. }) => {
+            assert!(msg.contains("attempt to load a binary chunk"))
+        }
+        Err(e) => panic!("expected SyntaxError, got {:?}", e),
+    };
+
+    Ok(())
+}
+
 #[test]
 fn test_lua_multi() -> Result<()> {
     let lua = Lua::new();
@@ -457,7 +523,9 @@ fn test_num_conversion() -> Result<()> {
     assert!(lua.load("math.huge").eval::<i64>().is_err());
 
     assert_eq!(lua.unpack::<f64>(lua.pack(f32::MAX)?)?, f32::MAX as f64);
-    assert!(lua.unpack::<f32>(lua.pack(f64::MAX)?).is_err());
+    assert_eq!(lua.unpack::<f64>(lua.pack(f32::MIN)?)?, f32::MIN as f64);
+    assert_eq!(lua.unpack::<f32>(lua.pack(f64::MAX)?)?, f32::INFINITY);
+    assert_eq!(lua.unpack::<f32>(lua.pack(f64::MIN)?)?, f32::NEG_INFINITY);
 
     assert_eq!(lua.unpack::<i128>(lua.pack(1i128 << 64)?)?, 1i128 << 64);