Fix modutils._is_subpath to handle base with trailing os.sep

[davidfstr]

Type of Changes

	Type
✓	🐛 Bug fix

Description

Currently on Windows if PATH contains a UNC path like r"\\Mac\Code\" with a trailing slash, modutils.modpath_from_file won't be able to locate .py files like r"\\Mac\Code\tests\test_resources.py" inside such a path. Consequently, astroid will refuse to load the source code for .py files in such locations.

This change fixes the underlying modutils._is_subpath function used by modutils.modpath_from_file to handle paths with trailing os.sep correctly.

---

I would have preferred to update the ModPathFromFileTest test suite rather than creating a new IsSubpathTest suite, but ModPathFromFileTest is currently not passing on Windows.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.41%. Comparing base (e9571d8) to head (2d471d3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2928   +/-   ##
=======================================
  Coverage   93.41%   93.41%           
=======================================
  Files          92       92           
  Lines       11237    11237           
=======================================
  Hits        10497    10497           
  Misses        740      740           

Flag	Coverage Δ
linux	93.26% <100.00%> (ø)
pypy	93.41% <100.00%> (ø)
windows	93.39% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
astroid/modutils.py	89.61% <100.00%> (ø)

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[davidfstr]

In case anyone else is impacted by this issue and needs a quick fix, here's what I'm doing:

def _patch_astroid() -> None:
    """
    Patches astroid 4.0.3 to work with PATH entries that end with os.path.sep.
    
    Backports the fix: https://github.com/pylint-dev/astroid/pull/2928
    """
    if sys.platform != 'win32':
        # Patch only useful on Windows
        return
    try:
        import astroid.modutils
    except ImportError:
        pass
    else:
        path = '\\\\Mac\\Code\\tests\\test_resources.py'
        base = '\\\\mac\\code\\'
        if not astroid.modutils._is_subpath(path, base):
            def _is_subpath2(path: str, base: str) -> bool:
                path = os.path.normcase(os.path.normpath(path))
                base = os.path.normcase(os.path.normpath(base))
                if not path.startswith(base):
                    return False
                return (
                    (len(path) == len(base)) or 
                    (path[len(base)] == os.path.sep) or
                    # Fix
                    (base.endswith(os.path.sep) and path[len(base) - 1] == os.path.sep)
                )
            astroid.modutils._is_subpath = _is_subpath2
        assert astroid.modutils._is_subpath(path, base)