Fix Analyzer-CFE integration issue where a mixin extends an abstract class

[scheglov]

[chloestefantsova]

@scheglov Could you please provide more details? I've written the following example program and it compiles under CFE and its behavior is what I would expect it to be.

class M {
  void foo() {
    print("M.foo");
  }
}

class N extends M {
  void foo() {
    super.foo();
  }
}

class B {
  void foo() {
    print("B.foo");
  }
}

class C extends B with N {}

main() {
  C c = new C();
  c.foo();
}

When run in the current master branch, it prints out the following:

$ out/ReleaseX64/dart /tmp/example.dart
B.foo

[scheglov]

I'm sorry, it was too global statement.
What I should have said is that a test fails with CFE.
I don't fully aware about all details of super-mixin semantics.
@bwilkerson added this test in https://codereview.chromium.org/2500143002

[chloestefantsova]

Thanks for the clarification, Konstantin! I think this is the part of the spec that the test is checking: link. I've renamed the issue accordingly.

Also, here's the discussed test for convenience:

abstract class A {
  void test();
}

class B extends A {
  void test() {
    super.test;
  }
}

It should compile without warnings or errors when the super-mixin feature is enabled. Currently CFE produces a compile-time error.

[chloestefantsova]

I did some research and it seems that the discussed example works in CFE if B is made abstract and enableSuperMixins is set to true. The former is reported by @bwilkerson in #33951, and I have a fix in CL 66380 for the latter.

[chloestefantsova]

Blocked on #33951.

[chloestefantsova]

As per Leaf's comment on #33951, I believe there's nothing more to be done here after CL 66380.