Mismatched method signature in mixin invocationDRT-W1484

The analyzer produces this diagnostic when a mixin that invokes a method using super is used in a class where the concrete implementation of that method has a different signature than the signature defined for that method by the mixin's on type. The reason this is an error is because the invocation in the mixin might invoke the method in a way that's incompatible with the method that will actually be executed.

Example

The following code produces this diagnostic because the class C uses the mixin M, the mixin M invokes foo using super, and the abstract version of foo declared in I (the mixin's on type) doesn't have the same signature as the concrete version of foo declared in A:

class I {
  void foo([int? p]) {}
}

class A {
  void foo(int p) {}
}

abstract class B extends A implements I {
  @override
  void foo([int? p]);
}

mixin M on I {
  void bar() {
    super.foo(42);
  }
}

abstract class C extends B with M {}

Common fixes

If the class doesn't need to use the mixin, then remove it from the with clause:

class I {
  void foo([int? p]) {}
}

class A {
  void foo(int? p) {}
}

abstract class B extends A implements I {
  @override
  void foo([int? p]);
}

mixin M on I {
  void bar() {
    super.foo(42);
  }
}

abstract class C extends B {}

If the class needs to use the mixin, then ensure that there's a concrete implementation of the method that conforms to the signature expected by the mixin:

class I {
  void foo([int? p]) {}
}

class A {
  void foo(int? p) {}
}

abstract class B extends A implements I {
  @override
  void foo([int? p]) {
    super.foo(p);
  }
}

mixin M on I {
  void bar() {
    super.foo(42);
  }
}

abstract class C extends B with M {}