Proposal: Drop the traceback from the module-level backend error objects.

[yilei]

Why? These are module-level objects that will live forever. Normally this is fine. But if we lazily import pathspec in somewhere deep in the Python program (or with the upcoming PEP 810 explicit lazy import in Python 3.15), it will hold the traceback, thus the locals of each frame, in memory forever.

We ran into such case where we might hold GBs of memory because of this edge case.

As far as I can tell, we don't really need the traceback on the exception object here.

What do you think? I can totally understand this seems to be out of the blue optimization for super rare edge cases.

Thanks for your consideration in advance!

[cpburnz]

It is obscure, but there's no strong benefit of keeping the original traceback. This is with the original traceback:

>>> pathspec.PathSpec.from_lines('gitignore', [], backend='re2')
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    pathspec.PathSpec.from_lines('gitignore', [], backend='re2')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/caleb/Downloads/venv/lib/python3.14/site-packages/pathspec/pathspec.py", line 261, in from_lines
    return cls(patterns, backend=backend, _test_backend_factory=_test_backend_factory)
  File "/home/caleb/Downloads/venv/lib/python3.14/site-packages/pathspec/pathspec.py", line 82, in __init__
    use_backend = self._make_backend(backend, patterns)
  File "/home/caleb/Downloads/venv/lib/python3.14/site-packages/pathspec/pathspec.py", line 281, in _make_backend
    return make_pathspec_backend(name, patterns)
  File "/home/caleb/Downloads/venv/lib/python3.14/site-packages/pathspec/_backends/agg.py", line 100, in make_pathspec_backend
    return Re2PsBackend(cast(Sequence[RegexPattern], patterns))
  File "/home/caleb/Downloads/venv/lib/python3.14/site-packages/pathspec/_backends/re2/pathspec.py", line 58, in __init__
    raise re2_error
  File "/home/caleb/Downloads/venv/lib/python3.14/site-packages/pathspec/_backends/re2/_base.py", line 17, in <module>
    import re2
ModuleNotFoundError: No module named 're2'

And this is using your change to remove the original traceback:

>>> pathspe.PathSpec.from_lines('gitignore', [], backend='re2')
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    pathspec.PathSpec.from_lines('gitignore', [], backend='re2')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/pathspec.py", line 267, in from_lines
    return cls(patterns, backend=backend, _test_backend_factory=_test_backend_factory)
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/pathspec.py", line 82, in __init__
    use_backend = self._make_backend(backend, patterns)
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/pathspec.py", line 287, in _make_backend
    return make_pathspec_backend(name, patterns)
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/_backends/agg.py", line 100, in make_pathspec_backend
    return Re2PsBackend(cast(Sequence[RegexPattern], patterns))
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/_backends/re2/pathspec.py", line 58, in __init__
    raise re2_error
ModuleNotFoundError: No module named 're2'

I don't think keeping the original traceback adds any important information, particularly because the exception remains a clear ModuleNotFoundError exception. And the odd case of pyre2 being installed isn't any less clear:

>>> pathspec.PathSpec.from_lines('gitignore', [], backend='re2')
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    pathspec.PathSpec.from_lines('gitignore', [], backend='re2')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/pathspec.py", line 267, in from_lines
    return cls(patterns, backend=backend, _test_backend_factory=_test_backend_factory)
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/pathspec.py", line 82, in __init__
    use_backend = self._make_backend(backend, patterns)
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/pathspec.py", line 287, in _make_backend
    return make_pathspec_backend(name, patterns)
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/_backends/agg.py", line 100, in make_pathspec_backend
    return Re2PsBackend(cast(Sequence[RegexPattern], patterns))
  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/_backends/re2/pathspec.py", line 58, in __init__
    raise re2_error
AttributeError: module 're2' has no attribute 'Options'

with this missing:

  File "/home/caleb/Personal/Projects/python/python-pathspec/pathspec/_backends/re2/_base.py", line 27, in <module>
    RE2_OPTIONS = re2.Options()
                  ^^^^^^^^^^^

Thanks.

[yilei]

Thank you for taking a close look at the tracebacks and merging my PR!