From 4003ef658581124dd7e9489a5f83912fafacbcaa Mon Sep 17 00:00:00 2001
From: Stefan Lau <github@stefanlau.com>
Date: Fri, 24 Apr 2026 15:53:05 +0200
Subject: [PATCH] fix Option<Self> in function/method parameters and returns

---
 src/typed/mod.rs   |  10 +++-
 tests/recursive.rs | 130 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 139 insertions(+), 1 deletion(-)
 create mode 100644 tests/recursive.rs

diff --git a/src/typed/mod.rs b/src/typed/mod.rs
index 971194d..e6c0eb7 100644
--- a/src/typed/mod.rs
+++ b/src/typed/mod.rs
@@ -124,7 +124,15 @@ impl<T: Typed> Typed for Variadic<T> {
 /// {type} | nil
 impl<T: Typed> Typed for Option<T> {
     fn ty() -> Type {
-        Type::Union(vec![T::ty(), Type::Single("nil".into())])
+        T::ty() | Type::nil()
+    }
+
+    fn as_param() -> Type {
+        T::as_param() | Type::nil()
+    }
+
+    fn as_return() -> Type {
+        T::as_return() | Type::nil()
     }
 }
 
diff --git a/tests/recursive.rs b/tests/recursive.rs
new file mode 100644
index 0000000..85292bf
--- /dev/null
+++ b/tests/recursive.rs
@@ -0,0 +1,130 @@
+#![cfg(all(feature = "mlua", feature = "derive"))]
+
+use mlua::{FromLua, MetaMethod, UserData, Value};
+use mlua_extras::{
+    Typed,
+    mlua::Lua,
+    typed::{
+        TypedDataFields, TypedDataMethods, TypedUserData, WrappedBuilder, generator::Definition,
+    },
+};
+
+#[derive(Default, Debug, Clone, Typed)]
+struct TestOption {
+    val: Option<String>,
+}
+
+impl FromLua for TestOption {
+    fn from_lua(value: Value, _lua: &Lua) -> mlua::Result<Self> {
+        let tn = value.type_name();
+        match value {
+            Value::UserData(usr_data) => {
+                if usr_data.is::<TestOption>() {
+                    return usr_data.take::<TestOption>();
+                }
+            }
+            _ => (),
+        }
+
+        Err(mlua::Error::FromLuaConversionError {
+            from: tn,
+            to: "TestOption".to_string(),
+            message: Some("failed to convert to userdata TestOption".into()),
+        })
+    }
+}
+
+impl UserData for TestOption {
+    fn add_fields<F: mlua::UserDataFields<Self>>(fields: &mut F) {
+        let mut wrapper = WrappedBuilder::new(fields);
+        TypedUserData::add_fields(&mut wrapper);
+    }
+
+    fn add_methods<M: mlua::UserDataMethods<Self>>(methods: &mut M) {
+        let mut wrapper = WrappedBuilder::new(methods);
+        TypedUserData::add_methods(&mut wrapper);
+    }
+}
+
+impl TypedUserData for TestOption {
+    fn add_fields<F: TypedDataFields<Self>>(fields: &mut F) {
+        fields.add_field_method_get("val", |_, this| Ok(this.val.clone()));
+    }
+
+    fn add_methods<T: TypedDataMethods<Self>>(methods: &mut T) {
+        methods.add_function(
+            "func_returns_option_self",
+            |_, ()| -> mlua::Result<Option<Self>> { Ok(Some(Self::default())) },
+        );
+        methods.add_function(
+            "func_takes_option_self",
+            |_, s: Option<Self>| -> mlua::Result<Self> {
+                Ok(Self {
+                    val: s.and_then(|v| v.val.clone()),
+                })
+            },
+        );
+
+        methods.add_method("clone", |_, this, ()| Ok(this.clone()));
+        methods.add_method(
+            "method_returns_option_self",
+            |_, _this, ()| -> mlua::Result<Option<Self>> { Ok(None) },
+        );
+        methods.add_method(
+            "method_takes_option_self",
+            |_, _this, v: Option<Self>| -> mlua::Result<Option<String>> {
+                Ok(v.and_then(|v| v.val).map(|v| v.to_string()))
+            },
+        );
+
+        methods.add_meta_method(MetaMethod::ToString, |_, this, ()| {
+            Ok(match this.val.as_ref() {
+                Some(val) => val.clone(),
+                None => "nil".to_owned(),
+            })
+        });
+    }
+}
+
+#[test]
+fn test_recursive_types_in_methods() {
+    let lua = Lua::new();
+
+    // Using it works fine
+    lua.globals().set("obj", TestOption::default()).unwrap();
+    let val: String = lua.load("return tostring(obj)").eval().unwrap();
+    assert_eq!(val, "nil");
+
+    lua.globals().set("obj", TestOption::default()).unwrap();
+    let val: String = lua
+        .load("return tostring(obj.func_returns_option_self())")
+        .eval()
+        .unwrap();
+    assert_eq!(val, "nil");
+
+    lua.globals().set("obj", TestOption::default()).unwrap();
+    let val: String = lua
+        .load("return tostring(obj.func_takes_option_self(obj))")
+        .eval()
+        .unwrap();
+    assert_eq!(val, "nil");
+
+    lua.globals().set("obj", TestOption::default()).unwrap();
+    let val: String = lua
+        .load("return tostring(obj:method_returns_option_self())")
+        .eval()
+        .unwrap();
+    assert_eq!(val, "nil");
+
+    lua.globals().set("obj", TestOption::default()).unwrap();
+    let val: String = lua
+        .load("local s = obj:clone():method_takes_option_self(obj); return tostring(s)")
+        .eval()
+        .unwrap();
+    assert_eq!(val, "nil");
+
+    Definition::start()
+        .register::<TestOption>("Example")
+        .value::<TestOption>("obj")
+        .finish();
+}