for-in inference broken in dev.17.0

[natebosch]

When the iterable in a for-in loop needs inference the variable doesn't get the right inferred type. Examples shown with implicit-casts: false, but the broken inference can cause problems in other ways without that option - such as no good feedback in the IDE

An example:

Broken:

void doStuff(int x) {}

void main() {
  var ints = [1];
  for (var x in ints.map((i) => i)) {
    doStuff(x); // The argument type 'dynamic' can't be assigned to the parameter type 'int'.
  }
}

Working if you add a variable so the type is already inferred:

void doStuff(int x) {}

void main() {
  var ints = [1];
  var intermediate = ints.map((i) => i);
  for (var x in intermediate) {
    doStuff(x); // No static error
  }
}

Also works if you force the type of the loop variable

void doStuff(int x) {}

void main() {
  var ints = [1];
  for (int x in ints.map((i) => i)) { // No static error
    doStuff(x);
  }
}

cc @munificent

[lrhn]

Also, shouldn't the dynamic typed expression be down-cast'able to any type?
(Or is this code analyzed with "no implicit downcasts"?)

[natebosch]

Or is this code analyzed with "no implicit downcasts"?

Yes, we're using implicit-casts: false here

[leafpetersen]

Seems to be fixed in dev.18