Lint unrelated_type_equality_checks no longer recognizes Int64, Int32.

[lrhn]

The lint unrelated_type_equality_checks has special-casing recognizing Int64 and Int32 from package:fixnum, to allow them to be compared to integers (which are otherwise an unrelated type).

This recognition fails after a refactoring of package:fixnum, which moved the classes into individual libraries, instead of using part files.

To Reproduce
Use tip-of-tree code from https://github.com/dart-lang/fixnum

Try to do if (FixNum(1) == 1) ... with the lint enabled. This used to not give a warning. Now it does.

Expected behavior

The Int64 and Int32 classes should still be recognized and special cased.

Additional context

The relevant code is:

bool _isFixNumIntX(DartType type) {
  if (type is! InterfaceType) {
    return false;
  }
  Element element = type.element;
  return (element.name == 'Int32' || element.name == 'Int64') &&
      element.library?.name == 'fixnum';
}

This approach depends on the package not changing, which is a fragile assumption to have for a separate package.

Consider instead checking whether the the classes are named Int32 or Int64, and the path to the library starts with package:fixnum/. That should cover most potential future refactorings of the package as well, because all it checks for is a class with one of those names provided by package:fixnum, without assuming anything about the internal structure of the package.

(That will make the lint harder to test, since you cannot just create a library with name fixnum and an Int64 type. Maybe retain the library name check as well, or change it to .name == 'fixnum_for_testing', so you can still trigger the lint without depending on package:fixnum. On the other hand, depending on the real package:fixnum for testing, as a dev-dependency, might help detecting if the lint breaks again.)

[pq]

Oh! This is a great heads-up. When is the refactored package scheduled to be released? If it's before Dart 3.0, we should hustle to get a fix in today (or cherry-picked) for 2.19.

[pq]

Ah. Chatting with @devoncarew, it sounds like this issue is blocking a roll of fixnum into Google3 too so yeah, we'd better get it addressed.

[devoncarew]

Yup, from https://github.com/dart-lang/sdk/blob/main/DEPS#L132, the roll issue is b/260609190.

[lrhn]

Solution looks good. Should work even if we end up doing different implementations for different platforms, so there'll be more than one Int64 class defined. They'll all be detected by this.