git's noprefix option breaks diff-cover

[beaugunderson]

I have this in my .gitconfig:

[diff]
	noprefix = true

This breaks diff-cover's regex, which expects there to be a/ and b/ prefixes in the diff output.

It's easy enough to disable the option, but I'd love to find a way to have the option for my normal use and have diff-cover still work. :)

[beaugunderson]

This is the stack, fwiw:

Traceback (most recent call last):
  File "/Users/beau/.envs/home/bin/diff-cover", line 10, in <module>
    sys.exit(main())
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/tool.py", line 350, in main
    src_roots=arg_dict['src_roots'],
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/tool.py", line 279, in generate_coverage_report
    reporter.generate_report(output_file)
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/report_generator.py", line 215, in generate_report
    report = template.render(self._context())
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/report_generator.py", line 259, in _context
    src: self._src_path_stats(src) for src in self.src_paths()
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/report_generator.py", line 83, in src_paths
    return {src for src, summary in self._diff_violations().items()
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/report_generator.py", line 175, in _diff_violations
    for src_path in self._diff.src_paths_changed()
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/diff_reporter.py", line 147, in src_paths_changed
    diff_dict = self._git_diff()
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/diff_reporter.py", line 198, in _git_diff
    diff_dict = self._parse_diff_str(diff_str)
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/diff_reporter.py", line 248, in _parse_diff_str
    sections_dict = self._parse_source_sections(diff_str)
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/diff_reporter.py", line 286, in _parse_source_sections
    src_path = self._parse_source_line(line)
  File "/Users/beau/.envs/home/lib/python3.7/site-packages/diff_cover/diff_reporter.py", line 410, in _parse_source_line
    raise GitDiffError(msg)
diff_cover.git_diff.GitDiffError: Could not parse source path in line 'diff --git home-app/.coveragerc home-app/.coveragerc'

[beaugunderson]

Looks like there's precedent to setting git options in GitDiffTool already:

        return execute([
            'git', '-c', 'diff.mnemonicprefix=no', 'diff',
            "{branch}...HEAD".format(branch=compare_branch),
            '--no-color',
            '--no-ext-diff'
        ])[0]

Disabling noprefix here fixed my problem:

        return execute([
            'git', '-c', 'diff.mnemonicprefix=no', '-c',
            'diff.noprefix=no', 'diff',
            "{branch}...HEAD".format(branch=compare_branch),
            '--no-color',
            '--no-ext-diff'
        ])[0]

[beaugunderson]

(will have a PR for this today, likely)