`typing._UnionGenericAlias` is unhashable in 3.14

[neutrinoceros]

Bug report

Bug description:

typing._UnionGenericAlias) became unshable somewhere between 3.13 and 3.14.0b1 (most likely in gh-105511)

import typing
hash(typing._UnionGenericAlias)

Traceback (most recent call last):
  File "<python-input-0>", line 2, in <module>
    hash(typing._UnionGenericAlias)
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: unhashable type: '_UnionGenericAliasMeta'

This was hit in a doctest from astropy: xref astropy/astropy#18126
To be clear, the test in question doesn't necessarily correspond to a real-life application; we're testing that our itersubclasses utility function works in a very broad case where we try to retrieve all defined subclasses of object, and do a bit of internal book-keeping using a set of already-visited classes. This used to work in Python 3.13 (and seems to have worked with no interruption for 10+ years), so it still seemed worth a shot to see if that would be considered a bug here. Otherwise, it should be possible to fix the function on our side to either special case this exact class, ignore any unhashable class, or avoid reequiring hashability altogether.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-133925: Make typing._UnionGenericAlias hashable #133929
• [3.14] gh-133925: Make typing._UnionGenericAlias hashable (GH-133929) #133936

[hugovk]

(most likely in gh-105511)

Git bisect agrees, cc @JelleZijlstra.

[JelleZijlstra]

It's because I added __eq__ but not __hash__ to the metaclass. Fix in #133929.

[neutrinoceros]

Is there a reason to keep this open after the fox was merged ?

[AlexWaygood]

no, this is done now that the 🦊 is merged

[neutrinoceros]

Thanks, all !