fix(exclude): match a pattern against the path, not only against its basename

[Eljees]

What happens today

--exclude matches each changed file against two strings: its basename and its absolute path.

basename = os.path.basename(path)
if self._fnmatch(basename, exclude):
    return True

absolute_path = os.path.abspath(path)
return self._fnmatch(absolute_path, exclude)

A pattern that names a directory matches neither. fnmatch("skipme.py", "sub/*") is false, and so is fnmatch("/repo/sub/skipme.py", "sub/*"), because fnmatch anchors at both ends. So --exclude "sub/*" excludes nothing, silently - no warning, no error, and a report that looks right until someone counts the files.

What does work is a bare filename (--exclude setup.py, the README's example) or a pattern that happens to start with a wildcard (--exclude "*sub/*", the form suggested in #265). That is why the same option looks broken to one person and fine to the next.

Measured before the change, on a repository with app.py and sub/skipme.py both uncovered:

$ diff-cover coverage.xml --compare-branch main --exclude 'sub/*'
app.py (0.0%): Missing lines 5-6
sub/skipme.py (0.0%): Missing lines 5-6
Total:   4 lines

and after:

$ diff-cover coverage.xml --compare-branch main --exclude 'sub/*'
app.py (0.0%): Missing lines 5-6
Total:   2 lines

The change

The path as the diff reports it - relative to the repository root - is matched too. The absolute-path match stays, normalised through to_unix_path so a pattern written with forward slashes behaves the same on Windows.

Tests

Four cases in test_git_path_selection: a directory pattern, the /** shape the README shows for include, a pattern that matches nothing, and two patterns at once. Three of them fail on main:

FAILED tests/test_diff_reporter.py::test_git_path_selection[include5-exclude5-expected5]
FAILED tests/test_diff_reporter.py::test_git_path_selection[include6-exclude6-expected6]
FAILED tests/test_diff_reporter.py::test_git_path_selection[include8-exclude8-expected8]
3 failed, 6 passed

With the change all nine pass, and tests/test_diff_reporter.py is green in full (45 passed).

The rest of the suite is unchanged by this: 12 integration failures plus one error show up identically on pristine main in this container, all of them Permission denied: 'pylint'.

Related

#265 asks how to exclude two directories and ends with a workaround rather than an answer; #449 is the same silent no-op seen from the config file. Neither needs a behaviour change beyond this one.

AI-assisted (LLM used for drafting); every change verified and tested by me.

[Bachmann1234]

Thanks for the pr!