mlua_derive: Fix hygiene of callback bindings in userdata_impl

Author: khvzak

mlua_derive/src/userdata/userdata_impl.rs

@@ -1,7 +1,7 @@
 use std::sync::atomic::{AtomicUsize, Ordering};
 
 use proc_macro::TokenStream;
-use proc_macro2::TokenStream as TokenStream2;
+use proc_macro2::{Span as Span2, TokenStream as TokenStream2};
 use quote::{format_ident, quote};
 use syn::spanned::Spanned;
 use syn::{
@@ -535,14 +535,16 @@ fn gen_arg_token(arg: &ArgInfo) -> TokenStream2 {
 /// Generate call arguments for invoking the original method.
 fn gen_call_args(info: &MethodInfo) -> TokenStream2 {
     let mut call_args: Vec<TokenStream2> = Vec::new();
+    let this = Ident::new("this", Span2::mixed_site());
+    let lua = Ident::new("lua", Span2::mixed_site());
 
     match info.self_kind {
         SelfKind::None => {}
-        _ => call_args.push(quote! { this }),
+        _ => call_args.push(quote! { #this }),
     }
 
     if info.lua.is_some() {
-        call_args.push(quote! { lua });
+        call_args.push(quote! { #lua });
     }
 
     for arg in &info.args {
@@ -555,17 +557,19 @@ fn gen_call_args(info: &MethodInfo) -> TokenStream2 {
 /// Generate call arguments for invoking the original async method.
 fn gen_async_call_args(info: &MethodInfo) -> TokenStream2 {
     let mut call_args: Vec<TokenStream2> = Vec::new();
+    let this = Ident::new("this", Span2::mixed_site());
+    let lua = Ident::new("lua", Span2::mixed_site());
 
     match info.self_kind {
         SelfKind::None => {}
-        SelfKind::Ref(RefKind::Mut | RefKind::OptionMut) => call_args.push(quote! { &mut this }),
-        SelfKind::Ref(_) => call_args.push(quote! { &this }),
-        SelfKind::Owned => call_args.push(quote! { this }),
+        SelfKind::Ref(RefKind::Mut | RefKind::OptionMut) => call_args.push(quote! { &mut #this }),
+        SelfKind::Ref(_) => call_args.push(quote! { &#this }),
+        SelfKind::Owned => call_args.push(quote! { #this }),
     }
 
     match info.lua {
-        Some(LuaArg::Ref) => call_args.push(quote! { &lua }),
-        Some(LuaArg::Owned) => call_args.push(quote! { lua }),
+        Some(LuaArg::Ref) => call_args.push(quote! { &#lua }),
+        Some(LuaArg::Owned) => call_args.push(quote! { #lua }),
         None => {}
     }
 
@@ -579,19 +583,25 @@ fn gen_async_call_args(info: &MethodInfo) -> TokenStream2 {
 /// Generate the closure params for the registration callback.
 fn gen_closure_params(info: &MethodInfo) -> TokenStream2 {
     let destructure = gen_closure_destructure(info);
+    let this = Ident::new("this", Span2::mixed_site());
+    let lua = Ident::new("lua", Span2::mixed_site());
+
     match info.self_kind {
-        SelfKind::None => quote! { |lua, #destructure| },
-        _ => quote! { |lua, this, #destructure| },
+        SelfKind::None => quote! { |#lua, #destructure| },
+        _ => quote! { |#lua, #this, #destructure| },
     }
 }
 
 /// Generate the closure params for an async registration callback.
 fn gen_async_closure_params(info: &MethodInfo) -> TokenStream2 {
     let destructure = gen_closure_destructure(info);
+    let this = Ident::new("this", Span2::mixed_site());
+    let lua = Ident::new("lua", Span2::mixed_site());
+
     match info.self_kind {
-        SelfKind::None => quote! { |lua, #destructure| },
-        SelfKind::Ref(RefKind::Mut) => quote! { |lua, mut this, #destructure| },
-        _ => quote! { |lua, this, #destructure| },
+        SelfKind::None => quote! { |#lua, #destructure| },
+        SelfKind::Ref(RefKind::Mut) => quote! { |#lua, mut #this, #destructure| },
+        _ => quote! { |#lua, #this, #destructure| },
     }
 }
 
@@ -603,19 +613,21 @@ fn gen_field_getter(
 ) -> TokenStream2 {
     let lua_name = lua_attr.name(fn_name);
     let call_args = gen_call_args(info);
+    let this = Ident::new("this", Span2::mixed_site());
+    let lua = Ident::new("lua", Span2::mixed_site());
 
     if lua_attr.infallible {
         return quote! {
-            registry.add_field_method_get(#lua_name, |lua, this| {
-                let _ = lua; // silence unused variable warning
+            registry.add_field_method_get(#lua_name, |#lua, #this| {
+                let _ = #lua; // silence unused variable warning
                 Ok(#type_path::#fn_name(#call_args))
             });
         };
     }
 
     quote! {
-        registry.add_field_method_get(#lua_name, |lua, this| {
-            let _ = lua; // silence unused variable warning
+        registry.add_field_method_get(#lua_name, |#lua, #this| {
+            let _ = #lua; // silence unused variable warning
             #type_path::#fn_name(#call_args)
         });
     }
@@ -629,21 +641,23 @@ fn gen_field_setter(
 ) -> TokenStream2 {
     let lua_name = lua_attr.name(fn_name);
     let call_args = gen_call_args(info);
+    let this = Ident::new("this", Span2::mixed_site());
+    let lua = Ident::new("lua", Span2::mixed_site());
 
     if lua_attr.infallible {
         let val_ident = info.args.first().map(|a| &a.ident);
         return quote! {
-            registry.add_field_method_set(#lua_name, |lua, this, #val_ident| {
-                let _ = lua; // silence unused variable warning
+            registry.add_field_method_set(#lua_name, |#lua, #this, #val_ident| {
+                let _ = #lua; // silence unused variable warning
                 Ok(#type_path::#fn_name(#call_args))
             });
         };
     }
 
     let val_ident = info.args.first().map(|a| &a.ident);
     quote! {
-        registry.add_field_method_set(#lua_name, |lua, this, #val_ident| {
-            let _ = lua; // silence unused variable warning
+        registry.add_field_method_set(#lua_name, |#lua, #this, #val_ident| {
+            let _ = #lua; // silence unused variable warning
             #type_path::#fn_name(#call_args)
         });
     }

tests/userdata_macro.rs

@@ -471,6 +471,48 @@ fn test_static_metamethods() {
     .unwrap();
 }
 
+#[derive(Clone, Debug, UserData)]
+struct Hygiene {
+    value: i32,
+}
+
+#[mlua::userdata_impl]
+impl Hygiene {
+    #[lua(infallible)]
+    fn new(value: i32) -> Self {
+        Hygiene { value }
+    }
+
+    // `this` must not clash with the generated receiver binding.
+    #[lua(infallible)]
+    fn add_this(&self, this: i32) -> i32 {
+        self.value + this
+    }
+
+    // `lua` must not clash either.
+    #[lua(infallible)]
+    fn add_lua(&self, lua: i32) -> i32 {
+        self.value + lua
+    }
+}
+
+#[test]
+fn test_param_name_hygiene() {
+    let lua = Lua::new();
+    lua.globals()
+        .set("Hygiene", lua.create_proxy::<Hygiene>().unwrap())
+        .unwrap();
+    lua.load(
+        r#"
+        local h = Hygiene.new(10)
+        assert(h:add_this(5) == 15, "add_this should be 10 + 5 = 15")
+        assert(h:add_lua(3) == 13, "add_lua should be 10 + 3 = 13")
+    "#,
+    )
+    .exec()
+    .unwrap();
+}
+
 #[cfg(feature = "async")]
 mod async_tests {
     use mlua::{Lua, Result, UserData};
@@ -507,6 +549,10 @@ mod async_tests {
             Ok(self.0 * factor)
         }
 
+        async fn add(&self, this: u64, lua: u64) -> Result<u64> {
+            Ok(self.0 + this + lua)
+        }
+
         async fn default_value() -> Result<u64> {
             Ok(42)
         }
@@ -541,6 +587,8 @@ mod async_tests {
             assert(val == 10, "expected 10, got " .. tostring(val))
             local doubled = c:multiply(3)
             assert(doubled == 30, "expected 30, got " .. tostring(doubled))
+            local summed = c:add(1, 2)
+            assert(summed == 13, "expected 10 + 1 + 2 = 13, got " .. tostring(summed))
             local inf = c:get_value_infallible()
             assert(inf == 10, "expected infallible 10, got " .. tostring(inf))
         "#,