Transformed type is not picked up with inference - Dart 2.0.0-dev.17

[kevmoo]

See https://travis-ci.org/dart-lang/pub_server/jobs/329567888#L442
Perhaps related to #31884

with

analyzer:
  strong-mode:
    implicit-casts: false

foo() async {
  String value;
  var thing = new Stream<List<int>>.fromIterable(<List<int>>[
    <int>[5]
  ]);

  await for (var item in thing.transform(UTF8.decoder)) {
    /// `error: A value of type 'dynamic' can't be assigned to a variable of type 'String'. (invalid_assignment at [pub_server] example/example.dart:29)`
    value = item;
  }
}

[kevmoo]

CC @lrhn

[lrhn]

That error message is very suspicious. There are no values with type dynamic.
I'm guessing it means that an expression with type dynamic is not assignable to String.

It looks very related to 31884. The type of item should be inferred as String, but apparently it isn't.

[leafpetersen]

I can reproduce in dev.17, but not in dev.18, assuming fixed.