Invalid implementation of `==` or `hashCode` in a constant set elementDRT-W1275

The analyzer produces this diagnostic when the class of object used as an element in a constant set literal implements either the == operator, the getter hashCode, or both. The implementation of constant sets uses both the == operator and the hashCode getter, so any implementation other than the ones inherited from Object requires executing arbitrary code at compile time, which isn't supported.

Example

The following code produces this diagnostic because the constant set contains an element whose type is C, and the class C overrides the implementation of ==:

class C {
  const C();

  bool operator ==(Object other) => true;
}

const set = {C()};

The following code produces this diagnostic because the constant set contains an element whose type is C, and the class C overrides the implementation of hashCode:

class C {
  const C();

  int get hashCode => 3;
}

const map = {C()};

Common fixes

If you can remove the implementation of == and hashCode from the class, then do so:

class C {
  const C();
}

const set = {C()};

If you can't remove the implementation of == and hashCode from the class, then make the set non-constant:

class C {
  const C();

  bool operator ==(Object other) => true;
}

final set = {C()};