docs/source/release-notes/5.0.1.rst

@@ -0,0 +1,15 @@
+5.0.1 -- 2022-07-31
+-------------------
+
+You can view the `5.0.1 milestone`_ on GitHub for more details.
+
+Bugs Fixed
+~~~~~~~~~~
+
+- Fix duplicate plugin discovery on misconfigured pythons (See also
+  :issue:`1627`, :pull:`1631`).
+
+
+.. all links
+.. _5.0.1 milestone:
+    https://github.com/PyCQA/flake8/milestone/43

docs/source/release-notes/index.rst

@@ -10,6 +10,7 @@ with the newest releases first.
 
 .. toctree::
    5.0.0
+   5.0.1
 
 4.x Release Series
 ==================

src/flake8/__init__.py

@@ -17,7 +17,7 @@
 LOG = logging.getLogger(__name__)
 LOG.addHandler(logging.NullHandler())
 
-__version__ = "5.0.0"
+__version__ = "5.0.1"
 __version_info__ = tuple(int(i) for i in __version__.split(".") if i.isdigit())
 
 _VERBOSITY_TO_LOG_LEVEL = {

src/flake8/plugins/finder.py

@@ -179,6 +179,8 @@ def _flake8_plugins(
 
 
 def _find_importlib_plugins() -> Generator[Plugin, None, None]:
+    # some misconfigured pythons (RHEL) have things on `sys.path` twice
+    seen = set()
     for dist in importlib_metadata.distributions():
         # assigned to prevent continual reparsing
         eps = dist.entry_points
@@ -190,6 +192,11 @@ def _find_importlib_plugins() -> Generator[Plugin, None, None]:
         # assigned to prevent continual reparsing
         meta = dist.metadata
 
+        if meta["name"] in seen:
+            continue
+        else:
+            seen.add(meta["name"])
+
         if meta["name"] in BANNED_PLUGINS:
             LOG.warning(
                 "%s plugin is obsolete in flake8>=%s",

src/flake8/style_guide.py

@@ -254,13 +254,10 @@ def populate_style_guides_with(
 
     def _style_guide_for(self, filename: str) -> "StyleGuide":
         """Find the StyleGuide for the filename in particular."""
-        guides = sorted(
+        return max(
             (g for g in self.style_guides if g.applies_to(filename)),
             key=lambda g: len(g.filename or ""),
         )
-        if len(guides) > 1:
-            return guides[-1]
-        return guides[0]
 
     @contextlib.contextmanager
     def processing_file(

tests/unit/plugins/finder_test.py

@@ -361,6 +361,23 @@ def test_importlib_plugins(
     ]
 
 
+def test_duplicate_dists(flake8_dist):
+    # some poorly packaged pythons put lib and lib64 on sys.path resulting in
+    # duplicates from `importlib.metadata.distributions`
+    with mock.patch.object(
+        importlib_metadata,
+        "distributions",
+        return_value=[
+            flake8_dist,
+            flake8_dist,
+        ],
+    ):
+        ret = list(finder._find_importlib_plugins())
+
+    # we should not have duplicates
+    assert len(ret) == len(set(ret))
+
+
 def test_find_local_plugins_nothing():
     cfg = configparser.RawConfigParser()
     assert set(finder._find_local_plugins(cfg)) == set()