Strong mode allows iterable to be assigned to list

[manuelF]

void main() {
  List<String> f = ['a', 'b']
  List<String> res = f.map((x) => x + 'aa');
  print(res)
}

$ dartanalyzer --strong file.dart
No issues found

$ dart file.dart
(aaa, baa)

$ dart --checked file.dart
type 'MappedListIterable' is not a subtype of type 'List' of 'res'

Shouldn't this at least produce a strong mode warning? Types are clearly not assignable.

[zoechi]

It does complain about missing semicolons though ;-) https://dartpad.dartlang.org/926c7d2430072eb7eacf72ea907a1f1f (including missing ;)

[leafpetersen]

This is potentially a valid downcast given the existing variance rules, and so we allow it. I hope to get an opt in flag for disabling these implicit downcasts implemented shortly. Closing this as a duplicate of #26583 which tracks that feature request.