GH-116380: Speed up glob.[i]glob() by making fewer system calls (take 2) - #137474

This was previously merged and then reverted because a newly-added test failed on one buildbot. I'm not sure that the test was ever valid, so I've removed it here.

Filtered recursive walk

Expanding a recursive ** segment entails walking the entire directory tree, and so any subsequent pattern segments (except special segments) can be evaluated by filtering the expanded paths through a regex. For example, glob.glob("foo/**/*.py", recursive=True) recursively walks foo/ with os.scandir(), and then filters paths through a regex based on "**/*.py, with no further filesystem access needed.

This fixes an issue where glob() could return duplicate results.

Tracking path existence

We store a flag alongside each path indicating whether the path is guaranteed to exist. As we process the pattern:

• Certain special pattern segments ("", "." and "..") leave the flag unchanged
• Literal pattern segments (e.g. foo/bar) set the flag to false
• Wildcard pattern segments (e.g. */*.py) set the flag to true (because children are found via os.scandir())
• Recursive pattern segments (e.g. **) leave the flag unchanged for the root path, and set it to true for descendants discovered via os.scandir().

If the flag is false at the end, we call lstat() on each path to filter out missing paths.

Minor speed-ups

• Exclude paths that don't match a non-terminal non-recursive wildcard pattern prior to calling is_dir().
• Use a stack rather than recursion to implement recursive wildcards.
  • This fixes a recursion error when globbing deep trees.
• Pre-compile regular expressions and pre-join literal pattern segments.
• Convert to/from bytes (a minor use-case) in iglob() rather than supporting bytes throughout. This particularly simplifies the code needed to handle relative bytes paths with dir_fd.
• Avoid calling os.path.join(); instead we keep paths in a normalized form and append trailing slashes when needed.
• Avoid calling os.path.normcase(); instead we use case-insensitive regex matching.

Implementation notes

Much of this functionality is already present in pathlib's implementation of globbing. The specific additions we make are:

1. Support for dir_fd
2. Support for include_hidden
3. Support for generating paths relative to root_dir
4. Support for suppressing the top-level path

This unifies the implementations of globbing in the glob and pathlib modules.

Results

Speedups via python -m timeit -s "from glob import glob" "glob(pattern, recursive=True, include_hidden=True)" from CPython source directory on Linux:

• Issue: Speed up glob.glob() by reducing number of system calls made #116380

📚 Documentation preview 📚: https://cpython-previews--137474.org.readthedocs.build/