fix(generic): avoid callable return fallback on shape miss

Author: lewis6991

crates/emmylua_code_analysis/src/compilation/test/callable_return_infer_test.rs

@@ -200,4 +200,34 @@ mod test {
         // unresolved and carried through a named callback value.
         assert_eq!(ws.expr_ty("classify_string_unresolved"), ws.ty("string"));
     }
+
+    #[test]
+    fn test_apply_return_infer_leaves_result_unknown_when_no_callable_member_matches_arg_shape() {
+        let mut ws = VirtualWorkspace::new();
+        ws.def(
+            r#"
+            ---@generic A, R
+            ---@param f fun(x: A): R
+            ---@param x A
+            ---@return R
+            local function apply(f, x)
+                return f(x)
+            end
+
+            ---@alias FnInt fun(x: integer): integer
+            ---@alias FnString fun(x: string): string
+
+            ---@type FnInt | FnString
+            local run
+
+            ---@type boolean
+            local b
+
+            result = apply(run, b)
+            "#,
+        );
+
+        let result_ty = ws.expr_ty("result");
+        assert_eq!(result_ty, ws.ty("unknown"));
+    }
 }

crates/emmylua_code_analysis/src/semantic/generic/instantiate_type/instantiate_func_generic.rs

@@ -267,7 +267,10 @@ pub fn infer_callable_return_from_remaining_args(
         return Ok(None);
     }
 
-    infer_callable_return_from_arg_types(context, callable_type, Some(&call_arg_types), true)
+    // If the remaining arg types are concrete and no callable member accepts them, leave the
+    // return unresolved instead of unioning returns from incompatible overloads. The broad
+    // fallback is only for cases where those arg shapes could not be inferred at all.
+    infer_callable_return_from_arg_types(context, callable_type, Some(&call_arg_types), false)
 }
 
 fn instantiate_callable_from_arg_types(