Diff-quality fails when source files have been deleted

[eacherkan-via]

Issue description

When git diff output includes deleted files, diff-quality invokes the quality tool without adding the source file path to the command line. Tools that require a list of input files (e.g. pycodestyle) will fail when invoked without it:

$ diff-quality --violations pycodestyle
diff_cover.command_runner.CommandError: Usage: pycodestyle [options] input ...

pycodestyle: error: input not specified

(Tools that allow to be invoked without a list of inputs won't fail, but likely won't produce the expected output either.)

Traceback

$ diff-quality --violations pycodestyle
Traceback (most recent call last):
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/report_generator.py", line 199, in _diff_violations
    violations = self._violations.violations_batch(src_paths_changed)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/violationsreporters/base.py", line 48, in violations_batch
    raise NotImplementedError
NotImplementedError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "[project-folder]/.venv/bin/diff-quality", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/diff_quality_tool.py", line 349, in main
    percent_passing = generate_quality_report(
                      ^^^^^^^^^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/diff_quality_tool.py", line 275, in generate_quality_report
    reporter.generate_report(output_file)
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/report_generator.py", line 302, in generate_report
    report = template.render(self._context())
                             ^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/report_generator.py", line 351, in _context
    context = super().report_dict()
              ^^^^^^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/report_generator.py", line 220, in report_dict
    src_stats = {src: self._src_path_stats(src) for src in self.src_paths()}
                                                           ^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/report_generator.py", line 86, in src_paths
    for src, summary in self._diff_violations().items()
                        ^^^^^^^^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/report_generator.py", line 211, in _diff_violations
    self._violations.violations(src_path),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/violationsreporters/base.py", line 171, in violations
    stdout, stderr = execute(command, self.driver.exit_codes)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "[project-folder]/.venv/lib/python3.12/site-packages/diff_cover/command_runner.py", line 36, in execute
    raise CommandError(stderr)
diff_cover.command_runner.CommandError: Usage: pycodestyle [options] input ...

pycodestyle: error: input not specified

[eacherkan-via]

From what I understand, this behavior comes from QualityReporter.violations:

    if os.path.exists(src_path):
        command.append(src_path.encode(sys.getfilesystemencoding()))

Why not skip the tool invocation if src_path doesn't exist?
Or, if some validation tools expect to be invoked in this scenario, then maybe each driver should declare whether it would like to be invoked without input paths or not.

On a semi-related note, if introducing the ability for each driver to decide "Don't invoke me with no inputs" or "Please invoke me even with no inputs", maybe this can be extended to "Invoke me with multiple inputs" so that tools that support it can be invoked once, instead of for each file separately.

[Bachmann1234]

Try https://pypi.org/project/diff-cover/9.7.0/ and let me know if it works better for you

[eacherkan-via]

It does! I verified that the issue is fixed in 9.7.0. Thanks @Bachmann1234, @CliveCorbishleyTAL!