gh-145028: Fix blake2 tests in test_hashlib when it is missing due to configure --without-builtin-hashlib-hashes

[tucif]

This PR addresses Issue #145028 tracking test_hashlib failure on cpython configured --without-builtin-hashlib-hashes

Changes in test_hashlib.py

• Guard testing of blake2 with existing utils to verify its existence (@require_blake2)
• Remove blake2 variations from algorithms in constructor when _blake2 is None, as they may already be in that list through its initialization from self.supported_hashnames.
• Add subtests in test_algorithms_available and skip if ValueError is raised, so it's easy to tell what exactly was skipped and why.
• Conditionally add blake2 on test*gil that had previously hardcoded it to their check lists.

Testing with fix on python without builtin blake2

python -m unittest Lib.test.test_hashlib.HashLibTestCase
...
----------------------------------------------------------------------
Ran 82 tests in 7.005s

OK (skipped=29)

Sample skips on test_algorithms_available

  test_algorithms_available (Lib.test.test_hashlib.HashLibTestCase.test_algorithms_available) [blake2b] ... skipped 'unsupported hash algorithm blake2b'
  test_algorithms_available (Lib.test.test_hashlib.HashLibTestCase.test_algorithms_available) [blake2s] ... skipped 'unsupported hash algorithm blake2s'

• Issue: test_hashlib blake2 tests fail on python configured --without-builtin-hashlib-hashes #145028

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[gpshead]

This basically skips the point of the test which is to ensure that everything is available as written. modify the skipping to only skip on blake2 if it was not configured to be available perhaps:

if ("blake2" in name and
    "blake2" not in sysconfig.get_config_var("PY_BUILTIN_HASHLIB_HASHES").split(",")):
    self.skipTest(verr)
else:
    raise

Given that blake2 is never going to be provided by a non-builtin.

[tucif]

Thanks for reviewing! Applied the suggestion.

[picnixz]

IIRC, you don't need to have the check here. find_gil_minsize() should skip the module if it can't be found (IIRC)

[tucif]

oh right, nice helper! removed this.

[picnixz]

Move the sysconfig stuff outside the loop please.

[tucif]

makes sense, done.

[picnixz]

Not sure that we need this guard here. Or do we?

[tucif]

Yeah seems like we do, if i remove it:

ERROR: test_threaded_hashing_fast (Lib.test.test_hashlib.HashLibTestCase.test_threaded_hashing_fast) [blake2s]
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/.../cpython/Lib/test/test_hashlib.py", line 1104, in test_threaded_hashing_fast
    self.do_test_threaded_hashing(constructor, is_shake=False)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/.../cpython/Lib/test/test_hashlib.py", line 1134, in do_test_threaded_hashing
    h1 = constructor(usedforsecurity=False)
  File "<string>", line 14, in blake2s
ValueError: unsupported hash algorithm blake2s

[picnixz]

An alternative is to simply catch the valueerror and skip the test otherwise. I don't think we're very consistent here.