Private field is promotable in spite of noSuchMethod forwarder

[sgrekhov]

The following test fails in both analyzer and CFE

class A {
  final int? _x = 42;

  void testA() {
    if (_x != null) {
      _x.isOdd;  // No expected error
//       ^^^^^
// [analyzer] unspecified
// [cfe] unspecified
    }
  }
}

class C {
  void _x();

  dynamic noSuchMethod(Invocation inv) {}
}

main() {
  A a = A();
  if (a._x is int) {
    a._x.isEven;  // No expected error
//       ^^^^^^
// [analyzer] unspecified
// [cfe] unspecified
  }
  a.testA();
}

According to the dart-lang/language#2020 (comment) if there is an implicit noSuchMethod forwarder in the same library field should not be promotable

cc @stereotype441

Tested on Dart SDK version: 3.2.0-edge.655687db777cf07cb4d75398f9eaf2d30ab6af44 (be) (Wed Sep 13 02:35:01 2023 +0000) on "macos_x64"

[eernstg]

True, this is what the spec-comment says.

However, @stereotype441, perhaps this is overkill? I'd expect that a forwarder for a method would never interfere with the getter of a final instance variable. Perhaps it is enough to cancel the promotion when there is a noSuchMethod forwarder with the same name which is a getter?

[stereotype441]

Sorry, that comment doesn't reflect what I actually implemented. What I actually implemented was exactly what @eernstg suggested, namely that a forwarder for a method does not interfere with the getter of a final instance variable. Promotion is only cancelled if there is a noSuchMethod forwarder with the same name which is a getter. I've updated that comment accordingly.

So in @sgrekhov's example, no error should be reported. Which matches the behaviour as of b555e71.

I'm assigning this issue to myself as a reminder to update the text in the CHANGELOG to reflect this subtlety.