mlua_derive: Switch from #[userdata] to [derive(UserData)]

Author: khvzak

examples/userdata.rs

@@ -1,7 +1,6 @@
-use mlua::{Lua, Result, chunk};
+use mlua::{Lua, Result, UserData, chunk};
 
-#[derive(Default)]
-#[mlua::userdata]
+#[derive(Default, UserData)]
 struct Rectangle {
     length: u32,
     width: u32,

mlua_derive/src/lib.rs

@@ -33,11 +33,11 @@ pub fn from_lua(input: TokenStream) -> TokenStream {
     from_lua::from_lua(input)
 }
 
-/// Attribute macro for exposing a Rust type as a Lua userdata.
+/// Derive macro for implementing `UserData` for a Rust type.
 #[cfg(feature = "macros")]
-#[proc_macro_attribute]
-pub fn userdata(attr: TokenStream, item: TokenStream) -> TokenStream {
-    userdata::userdata_type(attr, item)
+#[proc_macro_derive(UserData, attributes(lua))]
+pub fn userdata(item: TokenStream) -> TokenStream {
+    userdata::userdata_type(item)
 }
 
 /// Attribute macro for exposing impl block methods to Lua userdata.

mlua_derive/src/userdata/mod.rs

@@ -34,35 +34,18 @@ fn parse_field_lua_attr(attrs: &[Attribute]) -> syn::Result<LuaAttr> {
     Ok(lua_attr)
 }
 
-/// Strip `#[lua(...)]` attributes from a field, keeping all others.
-fn strip_lua_attrs(attrs: &[Attribute]) -> Vec<Attribute> {
-    (attrs.iter())
-        .filter(|attr| !attr.path().is_ident("lua"))
-        .cloned()
-        .collect()
-}
-
-pub fn userdata_type(attr: TokenStream, item: TokenStream) -> TokenStream {
-    if !attr.is_empty() {
-        return Error::new_spanned(
-            proc_macro2::TokenStream::from(attr),
-            "`#[userdata]` does not accept arguments",
-        )
-        .to_compile_error()
-        .into();
-    }
-
-    let mut input = parse_macro_input!(item as DeriveInput);
+pub fn userdata_type(item: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(item as DeriveInput);
     let type_name = &input.ident;
 
-    let mut named_fields: Option<&mut FieldsNamed> = match &mut input.data {
-        Data::Struct(data) => match &mut data.fields {
+    let named_fields: Option<&FieldsNamed> = match &input.data {
+        Data::Struct(data) => match &data.fields {
             Fields::Named(fields) => Some(fields),
             Fields::Unnamed(_) | Fields::Unit => None,
         },
         Data::Enum(_) => None,
         Data::Union(_) => {
-            return Error::new_spanned(&input, "`#[userdata]` cannot be applied to unions")
+            return Error::new_spanned(&input, "`#[derive(UserData)]` cannot be applied to unions")
                 .to_compile_error()
                 .into();
         }
@@ -73,14 +56,14 @@ pub fn userdata_type(attr: TokenStream, item: TokenStream) -> TokenStream {
     if has_type_params {
         return Error::new_spanned(
             &input.generics,
-            "`#[userdata]` does not support generic type parameters. Wrap the generic type in a concrete newtype instead."
+            "`#[derive(UserData)]` does not support generic type parameters. Wrap the generic type in a concrete newtype instead."
         )
         .to_compile_error()
         .into();
     }
 
     let mut field_registrations = Vec::new();
-    if let Some(fields) = &mut named_fields {
+    if let Some(fields) = &named_fields {
         for field in &fields.named {
             let field_name = field.ident.as_ref().unwrap();
 
@@ -114,19 +97,12 @@ pub fn userdata_type(attr: TokenStream, item: TokenStream) -> TokenStream {
                 field_registrations.push(with_cfg(tokens, &field.attrs));
             }
         }
-
-        // Strip mlua-specific attributes from fields before re-emitting
-        for field in &mut fields.named {
-            field.attrs = strip_lua_attrs(&field.attrs);
-        }
     }
 
     let registration_type_name = format_ident!("__MluaUserDataRegistration_{type_name}");
     let register_fields_fn_name = format_ident!("__mlua_register_{type_name}_fields");
 
     let output = quote! {
-        #input
-
         #[doc(hidden)]
         #[allow(non_camel_case_types)]
         struct #registration_type_name {

src/lib.rs

@@ -233,16 +233,14 @@ pub use mlua_derive::chunk;
 #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
 pub use mlua_derive::FromLua;
 
-/// Attribute macro for exposing a struct as Lua userdata.
+/// Derive macro for implementing [`UserData`] for a Rust type.
 ///
-/// All fields are auto-exposed as get/set.
+/// Named fields are auto-exposed as get/set.
 ///
 /// Use `#[lua(...)]` to customize.
-///
-/// This generates a [`UserData`] trait implementation.
 #[cfg(feature = "macros")]
 #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
-pub use mlua_derive::userdata;
+pub use mlua_derive::UserData;
 
 /// Attribute macro for exposing impl block methods to Lua userdata.
 ///

tests/compile/userdata_const_getter.rs

@@ -1,5 +1,4 @@
-#[derive(Default)]
-#[mlua::userdata]
+#[derive(Default, mlua::UserData)]
 struct Foo;
 
 #[mlua::userdata_impl]

tests/compile/userdata_const_getter.stderr

@@ -1,5 +1,5 @@
 error: const items do not support `getter` or `setter`
- --> tests/compile/userdata_const_getter.rs:8:11
+ --> tests/compile/userdata_const_getter.rs:7:11
   |
-8 |     const X: u32 = 42;
+7 |     const X: u32 = 42;
   |           ^

tests/compile/userdata_field_async.rs

@@ -1,7 +1,6 @@
 use mlua::Result;
 
-#[derive(Clone, Debug)]
-#[mlua::userdata]
+#[derive(Clone, Debug, mlua::UserData)]
 struct Foo;
 
 #[mlua::userdata_impl]

tests/compile/userdata_field_async.stderr

@@ -1,8 +1,8 @@
 error: async field function is not supported
-  --> tests/compile/userdata_field_async.rs:10:5
-   |
-10 |     async fn description() -> Result<String> {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ --> tests/compile/userdata_field_async.rs:9:5
+  |
+9 |     async fn description() -> Result<String> {
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused import: `mlua::Result`
  --> tests/compile/userdata_field_async.rs:1:5

tests/compile/userdata_field_with_args.rs

@@ -1,5 +1,4 @@
-#[derive(Default)]
-#[mlua::userdata]
+#[derive(Default, mlua::UserData)]
 struct Foo {
     x: u32,
 }

tests/compile/userdata_field_with_args.stderr

@@ -1,5 +1,5 @@
 error: field function must not take arguments
-  --> tests/compile/userdata_field_with_args.rs:10:5
-   |
-10 |     fn as_name(name: &str) -> String {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ --> tests/compile/userdata_field_with_args.rs:9:5
+  |
+9 |     fn as_name(name: &str) -> String {
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^