cache uses filenames that might be too long on some systems

[hottwaj]

Describe the bug

Running black 24.1.0 (without --check) can produce filenames in user's cache folder that are too long for some filesystems e.g. eCryptFS only allows filenames that are 143 chars long

The resulting error is:

Traceback (most recent call last):
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/bin/black", line 8, in <module>
    sys.exit(patched_main())
  File "src/black/__init__.py", line 1593, in patched_main
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/click/decorators.py", line 26, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "src/black/__init__.py", line 703, in main
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/black/concurrency.py", line 101, in reformat_many
    loop.run_until_complete(
  File "/home/hottwaj/.pyenv/versions/3.10.2/lib/python3.10/asyncio/base_events.py", line 641, in run_until_complete
    return future.result()
  File "/home/hottwaj/.pyenv/versions/3.10.2/envs/test-venv/lib/python3.10/site-packages/black/concurrency.py", line 137, in schedule_formatting
    cache = Cache.read(mode)
  File "src/black/cache.py", line 67, in read
  File "/home/hottwaj/.pyenv/versions/3.10.2/lib/python3.10/pathlib.py", line 1288, in exists
    self.stat()
  File "/home/hottwaj/.pyenv/versions/3.10.2/lib/python3.10/pathlib.py", line 1095, in stat
    return self._accessor.stat(self, follow_symlinks=follow_symlinks)
OSError: [Errno 36] File name too long: '/home/hottwaj/.cache/black/24.1.0/cache.-.130.0.0.0.0.1.e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.0.e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.pickle'

Environment

• Black's version: 24.1.0
• OS and Python version: Linux, Python 3.10.2, home folder encrypted with eCryptFS

[JelleZijlstra]

Thanks for reporting. #4174 has a more detailed writeup.

I think we should do a few things:

• Merge the two hashed pieces in the cache key in one, so the name gets shorter.
• Add a test to ensure the cache filename isn't too long.
• As eCryptfs incompatibility introduced in 24.1.0 #4174 suggests, make it so reformatting still succeeds (with a warning) if cache creation fails.

We can put out an extra release (24.1.1) once that's done.

[JelleZijlstra]

Fix is merged. I think I'll release 24.1.1 either later today or tomorrow, depending on we get other bug reports that we'd want to address.

[khamaileon]

Fixed for me. thanks @JelleZijlstra and @hottwaj for reporting.