Bug 1623339 - [lint.flake8] Fix path filtering bug when specifying subdirectory of excluded path, r=linter-reviewers,sylvestre

Differential Revision: https://phabricator.services.mozilla.com/D67335

--HG--
rename : tools/lint/test/files/flake8/subdir/exclude/bad.py => tools/lint/test/files/flake8/subdir/exclude/exclude_subdir/bad.py
extra : moz-landing-system : lando

docs/code-quality/lint/linters/flake8.rst

@@ -1,7 +1,7 @@
 Flake8
 ======
 
-`Flake8 <https://flake8.readthedocs.io/en/latest/>`__ is a popular lint wrapper for python. Under the hood, it runs three other tools and
+`Flake8 <https://flake8.pycqa.org/en/latest/index.html>`__ is a popular lint wrapper for python. Under the hood, it runs three other tools and
 combines their results:
 
 * `pep8 <http://pep8.readthedocs.io/en/latest/>`__ for checking style
@@ -25,22 +25,12 @@ flake8.
 Configuration
 -------------
 
-Only directories explicitly whitelisted will have flake8 run against them. To enable flake8 linting
-in a source directory, it must be added to the ``include`` directive in ```tools/lint/flake8.lint``.
-If you wish to exclude a subdirectory of an included one, you can add it to the ``exclude``
-directive.
+Path configuration is defined in the root `.flake8`_ file. Please update this file rather than
+``tools/lint/flake8.yml`` if you need to exclude a new path. For an overview of the supported
+configuration, see `flake8's documentation`_.
 
-The default configuration file lives in ``topsrcdir/.flake8``. The default configuration can be
-overridden for a given subdirectory by creating a new ``.flake8`` file in the subdirectory. Be warned
-that ``.flake8`` files cannot inherit from one another, so all configuration you wish to keep must
-be re-defined.
-
-.. warning::
-
-    Only ``.flake8`` files that live in a directory that is explicitly included in the ``include``
-    directive will be considered. See `bug 1277851 <https://bugzilla.mozilla.org/show_bug.cgi?id=1277851>`__ for more details.
-
-For an overview of the supported configuration, see `flake8's documentation <https://flake8.readthedocs.io/en/latest/config.html>`__.
+.. _.flake8: https://searchfox.org/mozilla-central/source/.flake8
+.. _flake8's documentation: https://flake8.pycqa.org/en/latest/user/configuration.html
 
 Autofix
 -------

tools/lint/python/flake8.py

@@ -118,11 +118,19 @@ def lint(paths, config, **lintargs):
         tools/lint/mach_commands.py.
         """
         # Ignore exclude rules if `--no-filter` was passed in.
+        config.setdefault('exclude', [])
         if lintargs.get('use_filters', True):
-            config.setdefault('exclude', []).extend(self.options.exclude)
+            config['exclude'].extend(self.options.exclude)
+
+        # Since we use the root .flake8 file to store exclusions, we haven't
+        # properly filtered the paths through mozlint's `filterpaths` function
+        # yet. This mimics that though there could be other edge cases that are
+        # different. Maybe we should call `filterpaths` directly, though for
+        # now that doesn't appear to be necessary.
+        filtered = [p for p in paths if not any(p.startswith(e) for e in config['exclude'])]
 
         self.options.exclude = None
-        self.args = self.args + list(expand_exclusions(paths, config, root))
+        self.args = self.args + list(expand_exclusions(filtered, config, root))
 
         if not self.args:
             raise NothingToLint

tools/lint/test/files/flake8/subdir/exclude/exclude_subdir/bad.py

@@ -0,0 +1,5 @@
+# Unused import
+import distutils
+
+print("This is a line that is over 80 characters but under 100. It shouldn't fail.")
+print("This is a line that is over not only 80, but 100 characters. It should most certainly cause a failure.")

tools/lint/test/test_flake8.py

@@ -65,7 +65,7 @@ foo = ['A list of strings', 'that go over 80 characters', 'to test if autopep8 f
 
 def test_lint_excluded_file(lint, paths, config):
     # First file is globally excluded, second one is from .flake8 config.
-    files = paths('bad.py', 'subdir/exclude/bad.py')
+    files = paths('bad.py', 'subdir/exclude/bad.py', 'subdir/exclude/exclude_subdir')
     config['exclude'] = paths('bad.py')
     results = lint(files, config)
     print(results)
@@ -97,7 +97,7 @@ def test_lint_excluded_file_with_glob(lint, paths, config):
 def test_lint_excluded_file_with_no_filter(lint, paths, config):
     results = lint(paths('subdir/exclude'), use_filters=False)
     print(results)
-    assert len(results) == 2
+    assert len(results) == 4
 
 
 def test_lint_uses_custom_extensions(lint, paths):