Something is off with override checks in Kernel type checker

[peter-ahe-google]

Consider this program:

abstract class A<Result, Input> {
  Result f(Input v);
}

abstract class A0<Result, Input> extends A<Result, Input> {}

abstract class M extends A<num, num> {
  @override
  num f(num v) => null;
}

void main() {}

If I create this as a test case in pkg/front_end/testcases/issue.dart and run:

./pkg/front_end/tool/fasta testing strong/issue -DupdateExpectations=true -DskipVm=true

The program type checks. If I then add a bad mixin application:

class Bad<U> = A0<dynamic, dynamic> with M;

I get this error:

In M::f at file:///Users/ahe/w/dart-sdk/sdk/pkg/front_end/testcases/issue.dart:9:

    Incompatible override of #lib1::A::f with #lib1::M::f:
    
        type of parameter v is incompatible
        override declares dart.core::num
        super method declares #lib1::A::Input

Kernel:
|
|   @dart.core::override
|

Source:
|
|     num f(num v) => null;
|

Two problems with this error:

1. There's nothing wrong with the declaration of M.f. The error is actually on the mixin appliction.

2. The super method doesn't declare v to have the type Input. Someone forgot to perform substitution of type parameters.