feat: Implement default-field-values

crates/ide-diagnostics/src/handlers/type_mismatch.rs

@@ -1232,6 +1232,21 @@ fn f() {
     let (_, _, _, ..) = (true, 42);
      // ^^^^^^^^^^^^^ error: expected (bool, i32), found (bool, i32, {unknown})
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn diagnostics_inside_field_default_expr() {
+        check_diagnostics(
+            r#"
+struct Foo {
+    foo: i32 = {
+        let x = false;
+        x
+     // ^ error: expected i32, found bool
+    },
+}
 "#,
         );
     }