Strange Dart 11

main.dart

/*
Bad type inference causes breakage when making a type more precise in covariant
position.
*/

class A {
  const A();
}

const constA = const A();

A test() => A();

void main() {
  var a = test();
  if (identical(a, constA)) {
    a = A();
  }
  print(a);
}

/*
Now try to replace `test` with:

```
class B extends A {}

B test() => B();
```

The problem is that the inferred type of `a` becomes `B`, so `a = A()` is now a
type error.

The fix is to give `a` an explicit type:

```
A a = test();
```
*/