This comment was originally written by ngeoffray@google.com

Pete, which part of the Dart language specification says that it is required to emit a warning?

Added NeedsInfo label.

To be clear I believe that this should not be a warning.

I'm not sure how type inference relates the 'static types' referenced by the language spec.

This comment was originally written by ngeoffray@google.com

I wrote too fast, I meant "which part of the Dart language specification says that we should not emit a warning?"

Thing is, I don't think this is specified, so to avoid warnings, one needs to change type annotations.

cc @peter-ahe-google.
cc @johnniwinther.

So this is what the code should be?

if (f is Bar) {
  Bar b = f;
  if (b.isBar) {
    b.doSomething();
  }
}

The original syntax seems like a straightforward assumption, it's something even the Closure JS compiler can do.

So is this a language issue then?

cc @rakudrama.

This comment was originally written by ngeoffray@google.com

After talking to Johnni, yes this is a language issue. Until this is fixed, we need to do write what you wrote, or just not put a type annotation at the declaration of 'f'.

cc @gbracha.
Removed Area-Dart2JS label.
Added Area-Language, Triaged labels.

The analyzer is completely non-compliant with the spec, causing lots of confusion.

The spec required a warning, because we do not specify flow dependent type inference of any kind. It's a slippery slope. We can review it in a future release.

Set owner to @gbracha.
Removed Type-Defect label.
Added Type-Enhancement, Accepted labels.

Type promotion is in the language now (and has been for quite some time).