Guards don't promote in switch expressions

[munificent]

I'm looking into the issue reported in this tweet. I can repro it with:

main() {
  String? s = null;
  var length = switch (0) {
    _ when s != null => s.length,
    _ => 0,
  };

  switch (0) {
    case _ when s != null: s.length;
  };
}

The switch statement is fine, but the switch expression yields:

temp.dart:5:27: Error: Property 'length' cannot be accessed on 'String?' because it is potentially null.
Try accessing using ?. instead.
    _ when s != null => s.length,
                          ^^^^^^

Do we not do type promotion in switch expression guards?

@stereotype441

[stereotype441]

Yeah, this is a known issue that I discovered just before 3.0 shipped, when there was no longer time to cherry-pick a fix. The fix has been cherry-picked to stable, and will ship in 3.0.1.

Tracking issue is here: #52241

[stereotype441]

Duplicate of #52241