From 1f3dafa564ac05146b0dc874ba0bb8eed3c97797 Mon Sep 17 00:00:00 2001
From: Alex Orlenko <zxteam@protonmail.com>
Date: Sat, 30 May 2026 12:46:31 +0100
Subject: [PATCH] mlua_derive: Reject static field functions with args

---
 mlua_derive/src/userdata/userdata_impl.rs     |  8 ++++++++
 tests/compile.rs                              |  1 +
 tests/compile/userdata_field_with_args.rs     | 15 +++++++++++++++
 tests/compile/userdata_field_with_args.stderr |  5 +++++
 4 files changed, 29 insertions(+)
 create mode 100644 tests/compile/userdata_field_with_args.rs
 create mode 100644 tests/compile/userdata_field_with_args.stderr

diff --git a/mlua_derive/src/userdata/userdata_impl.rs b/mlua_derive/src/userdata/userdata_impl.rs
index 4dbadc6..a63eede 100644
--- a/mlua_derive/src/userdata/userdata_impl.rs
+++ b/mlua_derive/src/userdata/userdata_impl.rs
@@ -335,6 +335,14 @@ pub fn userdata_impl(attr: TokenStream, item: TokenStream) -> TokenStream {
                             .to_compile_error()
                             .into();
                     }
+                    if !info.args.is_empty() {
+                        return syn::Error::new_spanned(
+                            &method.sig,
+                            "field function must not take arguments",
+                        )
+                        .to_compile_error()
+                        .into();
+                    }
                     let lua_name = lua_attr.name(fn_name);
                     if lua_attr.meta {
                         let tokens = quote! {
diff --git a/tests/compile.rs b/tests/compile.rs
index 64d2fff..6bd8408 100644
--- a/tests/compile.rs
+++ b/tests/compile.rs
@@ -35,6 +35,7 @@ fn test_compilation() {
         t.compile_fail("tests/compile/userdata_static_with_self.rs");
         t.compile_fail("tests/compile/userdata_meta_owned_self.rs");
         t.compile_fail("tests/compile/userdata_const_getter.rs");
+        t.compile_fail("tests/compile/userdata_field_with_args.rs");
     }
 
     #[cfg(all(feature = "macros", feature = "async"))]
diff --git a/tests/compile/userdata_field_with_args.rs b/tests/compile/userdata_field_with_args.rs
new file mode 100644
index 0000000..5394eaf
--- /dev/null
+++ b/tests/compile/userdata_field_with_args.rs
@@ -0,0 +1,15 @@
+#[derive(Default)]
+#[mlua::userdata]
+struct Foo {
+    x: u32,
+}
+
+#[mlua::userdata_impl]
+impl Foo {
+    #[lua(field)]
+    fn as_name(name: &str) -> String {
+        name.to_string()
+    }
+}
+
+fn main() {}
diff --git a/tests/compile/userdata_field_with_args.stderr b/tests/compile/userdata_field_with_args.stderr
new file mode 100644
index 0000000..c7ccf45
--- /dev/null
+++ b/tests/compile/userdata_field_with_args.stderr
@@ -0,0 +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 {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^