incorrect override error generated by front-end for mixin #32183
Description
class X {}
abstract class A<Result, Input> {
Result f(Input v);
}
abstract class A0<Result, Input> extends A<Result, Input> {
}
abstract class M extends A<X, num> implements X {
@override
M f(num v) => null;
}
class _C extends A0<X, num> with M {
}
void main() {
}results in
file:///tmp/xxx.dart:17:7: Error: The return type of the method '_C::f' is #lib1::X, which does not match the return type of the overridden method (#lib1::M).
Change to a subtype of #lib1::M.
class _C extends A0<X, num> with M {
^
file:///tmp/xxx.dart:14:5: Error: This is the overriden method ('f').
M f(num v) => null;
^This is most likely caused by the forwarding stub generated in _C
abstract class _A0&M^#U0&#U1^<#U0 extends core::Object, #U1 extends core::Ob
ject> extends xxx::A0<xxx::_A0&M^#U0&#U1^::#U0, xxx::_A0&M^#U0&#U1^::#U1> impl
ements xxx::M {
synthetic constructor •() → void
: super xxx::A0::•()
;
method f(generic-covariant-impl generic-covariant-interface core::num v) → xxx::M
return null;
}
class _C extends xxx::_A0&M^#U0&#U1^<xxx::X, core::num> {
synthetic constructor •() → void
: super xxx::A0::•()
;
abstract forwarding-stub method f(generic-covariant-impl core::num v) → xxx::X;
}
This example is extracted from package:file used by Flutter.