Fail to infer types of members in `on` classes.

[Cat-sushi]

With implicit-dynamic: false analysis option,
Dart SDK version: 2.19.0 (stable) (Unknown timestamp) on "linux_x64"
fails to infer types of members in on classes.

2.18.6 or former version of SDK didn't report any issue.

Missing field type for 'md'.
Try adding an explicit type, or remove implicit-dynamic from your analysis options file.dart(implicit_dynamic_field)

class C {
  double d = 0.0;
}

mixin M on C {
  late final md = d;
}

class C2 extends C with M {
}

void main(){
  var c = C2();
  print(c.md);
}

[Cat-sushi]

Is this related to #50383 ?

[asashour]

One can use

analyzer:
  language:
    strict-raw-types: true

instead of

analyzer:
  strong-mode:
    implicit-dynamic: false

There is a quick fix in the dev channel, but it seems it isn't there for 2.19.

[srawlins]

Hmm I find this to be very unexpected. Here's a slightly smaller example:

class C {
  double d = 0.0;
}

mixin M on C {
  late final md = d;
  
  void f() => md.x;
}

md.x should, I believe, be an error. In Dart 2.18 ("old" channel on DartPad) it is. In Dart 2.19, it is not. Our inference seems to have changed, such that the type of md is inferred to be dynamic.

CC @scheglov @stereotype441