From 58dd7df4ec8d04f74be26f935d756f2891d0c778 Mon Sep 17 00:00:00 2001
From: Sarah Wesker <sarahelizabetwesker@gmail.com>
Date: Thu, 26 Mar 2026 09:05:10 -0400
Subject: [PATCH 1/2] fix: handle Def types in object constraint duck typing

`check_object_type_compact` only matched `LuaType::Ref` when checking
if a class satisfies a structural object constraint (e.g. `{ x: number,
y: number, z: number }`). When the type was inferred as `LuaType::Def`
(e.g. from `return self` without an explicit `@return`), it fell through
to the wildcard arm and incorrectly reported a generic-constraint-mismatch.

Add `LuaType::Def` alongside `LuaType::Ref` in the match arm so both
representations are checked structurally against the object constraint.
---
 .../test/generic_constraint_mismatch_test.rs  | 41 +++++++++++++++++++
 .../complex_type/object_type_check.rs         |  2 +-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs b/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs
index 055a48e4e..0c6c47230 100644
--- a/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs
+++ b/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs
@@ -300,6 +300,47 @@ mod test {
         ));
     }
 
+    #[test]
+    fn test_object_constraint_with_class_ref() {
+        let mut ws = VirtualWorkspace::new();
+        // A @class whose inferred Def type (e.g. from `return self`) should satisfy
+        // an object constraint via structural duck typing, same as Ref types do.
+        assert!(ws.check_code_for(
+            DiagnosticCode::GenericConstraintMismatch,
+            r#"
+                ---@class MyPos
+                ---@field x number
+                ---@field y number
+                ---@field z number
+                ---@overload fun(x: number, y: number, z: number): MyPos
+                MyPos = {}
+                MyPos.__index = MyPos
+
+                setmetatable(MyPos, {
+                    __call = function(x, y, z)
+                        return setmetatable({ x = x, y = y, z = z }, MyPos)
+                    end
+                })
+
+                function MyPos:next()
+                    self.x = self.x + 1
+                    self.y = self.y + 1
+                    return self
+                end
+
+                ---@generic T: { x: number, y: number, z: number }
+                ---@param pos T
+                local function getTile(pos) end
+
+                local p = MyPos(0, 0, 0):next()
+                getTile(p)
+
+                local p2 = MyPos(1, 1, 1)
+                getTile(p2:next())
+            "#
+        ));
+    }
+
     #[test]
     fn test_generic_keyof_param_scope() {
         let mut ws = VirtualWorkspace::new();
diff --git a/crates/emmylua_code_analysis/src/semantic/type_check/complex_type/object_type_check.rs b/crates/emmylua_code_analysis/src/semantic/type_check/complex_type/object_type_check.rs
index 371c017b5..d1184b52b 100644
--- a/crates/emmylua_code_analysis/src/semantic/type_check/complex_type/object_type_check.rs
+++ b/crates/emmylua_code_analysis/src/semantic/type_check/complex_type/object_type_check.rs
@@ -35,7 +35,7 @@ pub fn check_object_type_compact(
                 check_guard.next_level()?,
             );
         }
-        LuaType::Ref(type_id) => {
+        LuaType::Ref(type_id) | LuaType::Def(type_id) => {
             return check_object_type_compact_type_ref(
                 context,
                 source_object,

From 2fc17d991e5bce170a2a331062480b17842ef27a Mon Sep 17 00:00:00 2001
From: Sarah Wesker <sarahelizabetwesker@gmail.com>
Date: Thu, 26 Mar 2026 09:25:04 -0400
Subject: [PATCH 2/2] rename

---
 .../src/diagnostic/test/generic_constraint_mismatch_test.rs     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs b/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs
index 0c6c47230..1e85409b1 100644
--- a/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs
+++ b/crates/emmylua_code_analysis/src/diagnostic/test/generic_constraint_mismatch_test.rs
@@ -301,7 +301,7 @@ mod test {
     }
 
     #[test]
-    fn test_object_constraint_with_class_ref() {
+    fn test_object_constraint_with_class_duck_typing() {
         let mut ws = VirtualWorkspace::new();
         // A @class whose inferred Def type (e.g. from `return self`) should satisfy
         // an object constraint via structural duck typing, same as Ref types do.