% ./python.exe -E -We -m test -v test_check_c_globals

...

test test_check_c_globals crashed -- Traceback (most recent call last):
  File "/Users/iritkatriel/src/cpython-1/Lib/test/libregrtest/runtest.py", line 335, in _runtest_inner
    refleak = _runtest_inner2(ns, test_name)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/test/libregrtest/runtest.py", line 280, in _runtest_inner2
    the_module = importlib.import_module(abstest)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1061, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1038, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1015, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 689, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 894, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/Users/iritkatriel/src/cpython-1/Lib/test/test_check_c_globals.py", line 6, in <module>
    from cpython.__main__ import main
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Tools/c-analyzer/cpython/__main__.py", line 18, in <module>
    from c_parser.info import KIND
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Tools/c-analyzer/c_parser/__init__.py", line 1, in <module>
    from .parser import parse as _parse
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Tools/c-analyzer/c_parser/parser/__init__.py", line 119, in <module>
    from ..info import ParsedItem
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Tools/c-analyzer/c_parser/info.py", line 10, in <module>
    import c_common.tables as _tables
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Tools/c-analyzer/c_common/tables.py", line 236, in <module>
    _COLSPEC_RE = re.compile(textwrap.dedent(r'''
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/re.py", line 229, in compile
    return _compile(pattern, flags)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/re.py", line 281, in _compile
    p = sre_compile.compile(pattern, flags)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/sre_compile.py", line 764, in compile
    p = sre_parse.parse(p, flags)
        ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/sre_parse.py", line 948, in parse
    p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/sre_parse.py", line 443, in _parse_sub
    itemsappend(_parse(source, state, verbose, nested + 1,
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/sre_parse.py", line 834, in _parse
    p = _parse_sub(source, state, sub_verbose, nested + 1)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/sre_parse.py", line 443, in _parse_sub
    itemsappend(_parse(source, state, verbose, nested + 1,
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-1/Lib/sre_parse.py", line 540, in _parse
    warnings.warn(
    ^^^^^^^^^^^^^^
FutureWarning: Possible nested set at position 12

test_check_c_globals failed (uncaught exception)

The warning comes from this regex: Tools/c-analyzer/c_common/tables.py", line 236

_COLSPEC_RE = re.compile(textwrap.dedent(r'''
    ^
    (?:
        [[]
        (
            (?: [^\s\]] [^\]]* )?
            [^\s\]]
        )  # <label>
        []]
    )?
    ( \w+ )  # <field>
    (?:
        (?:
            :
            ( [<^>] )  # <align>
            ( \d+ )  # <width1>
        )
        |
        (?:
            (?:
                :
                ( \d+ )  # <width2>
            )?
            (?:
                :
                ( .*? )  # <fmt>
            )?
        )
    )?
    $
'''), re.VERBOSE)

Yes, [[] looks as the start of a character set containing nested sets (e.g. "[[a-z]--[p-q]]"). This feature is supported by regex and can be added in future versions of re, breaking the code which contain such combinations.

New changeset 1a9ef5798525bbb39a16c8af5c435b97352ee027 by Serhiy Storchaka in branch 'main':
bpo-44786: Fix a warning in RE in c-analyzer (GH-28351)
https://github.com/python/cpython/commit/1a9ef5798525bbb39a16c8af5c435b97352ee027

New changeset 89966f59c2e1d0558f8126458acc7d7ae2a8fef5 by Miss Islington (bot) in branch '3.10':
bpo-44786: Fix a warning in RE in c-analyzer (GH-28351) (GH-28353)
https://github.com/python/cpython/commit/89966f59c2e1d0558f8126458acc7d7ae2a8fef5