parse default optional expressions in pattern matches

compiler/solve/tests/solve_expr.rs

@@ -2629,4 +2629,16 @@ mod solve_expr {
             "{ a : { x : Num a, y : Float, z : c }, b : { blah : Str, x : Num a, y : Float, z : c } }",
         );
     }
+
+    #[test]
+    fn optional_field_function() {
+        infer_eq_without_problem(
+            indoc!(
+                r#"
+                \{ x, y ? 0 } -> x + y
+                "#
+            ),
+            "{ x : Num a, y ? Num a }* -> Num a",
+        );
+    }
 }