From a7c5a24a7b725b8eb395aa28b0e3838c64ff2dbb Mon Sep 17 00:00:00 2001
From: Alex Orlenko <zxteam@protonmail.com>
Date: Sat, 30 May 2026 22:23:03 +0100
Subject: [PATCH] mlua_derive: Deny `#[lua = "..."]` syntax

---
 mlua_derive/src/userdata/mod.rs           | 18 ++++++++++++++----
 mlua_derive/src/userdata/userdata_impl.rs | 18 ++++++++++++++----
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/mlua_derive/src/userdata/mod.rs b/mlua_derive/src/userdata/mod.rs
index 83d91e3..4cbfd4e 100644
--- a/mlua_derive/src/userdata/mod.rs
+++ b/mlua_derive/src/userdata/mod.rs
@@ -25,10 +25,20 @@ pub(crate) fn with_cfg(tokens: proc_macro2::TokenStream, attrs: &[Attribute]) ->
 fn parse_field_lua_attr(attrs: &[Attribute]) -> syn::Result<LuaAttr> {
     let mut lua_attr = LuaAttr::default();
     for attr in attrs {
-        if attr.path().is_ident("lua")
-            && let Meta::List(_) = &attr.meta
-        {
-            attr.parse_nested_meta(|meta| lua_attr.parse_inner(meta))?;
+        if !attr.path().is_ident("lua") {
+            continue;
+        }
+        match &attr.meta {
+            Meta::List(_) => {
+                attr.parse_nested_meta(|meta| lua_attr.parse_inner(meta))?;
+            }
+            Meta::Path(_) => {}
+            Meta::NameValue(_) => {
+                return Err(syn::Error::new_spanned(
+                    attr,
+                    "`#[lua = \"...\"]` is not supported: use `#[lua(attr = \"...\")]`",
+                ));
+            }
         }
     }
     Ok(lua_attr)
diff --git a/mlua_derive/src/userdata/userdata_impl.rs b/mlua_derive/src/userdata/userdata_impl.rs
index a63eede..d082bb4 100644
--- a/mlua_derive/src/userdata/userdata_impl.rs
+++ b/mlua_derive/src/userdata/userdata_impl.rs
@@ -177,10 +177,20 @@ fn strip_item_attrs(attrs: &[Attribute]) -> Vec<Attribute> {
 fn parse_lua_attr(attrs: &[Attribute]) -> syn::Result<LuaAttr> {
     let mut lua_attr = LuaAttr::default();
     for attr in attrs {
-        if attr.path().is_ident("lua")
-            && let Meta::List(_) = &attr.meta
-        {
-            attr.parse_nested_meta(|meta| lua_attr.parse_inner(meta))?;
+        if !attr.path().is_ident("lua") {
+            continue;
+        }
+        match &attr.meta {
+            Meta::List(_) => {
+                attr.parse_nested_meta(|meta| lua_attr.parse_inner(meta))?;
+            }
+            Meta::Path(_) => {}
+            Meta::NameValue(_) => {
+                return Err(syn::Error::new_spanned(
+                    attr,
+                    "`#[lua = \"...\"]` is not supported: use `#[lua(attr = \"...\")]`",
+                ));
+            }
         }
     }
     Ok(lua_attr)