Prefer valid distributions when collecting entry points

importlib_metadata/__init__.py

@@ -1121,6 +1121,21 @@ def version(distribution_name: str) -> str:
 """
 
 
+def _unique_valid(dists: Iterable[Distribution]) -> Iterable[Distribution]:
+    """
+    Return unique distributions, preferring valid metadata for duplicates.
+    """
+    has_metadata = ExceptionTrap(MetadataNotFound).passes(operator.attrgetter('metadata'))
+    unique: dict[str, Distribution] = {}
+    for dist in dists:
+        name = dist._normalized_name
+        if name not in unique:
+            unique[name] = dist
+        elif not has_metadata(unique[name]) and has_metadata(dist):
+            unique[name] = dist
+    return unique.values()
+
+
 def entry_points(**params) -> EntryPoints:
     """Return EntryPoint objects for all installed packages.
 
@@ -1131,7 +1146,7 @@ def entry_points(**params) -> EntryPoints:
     :return: EntryPoints for all installed packages.
     """
     eps = itertools.chain.from_iterable(
-        dist.entry_points for dist in _unique(distributions())
+        dist.entry_points for dist in _unique_valid(distributions())
     )
     return EntryPoints(eps).select(**params)
 

tests/test_main.py

@@ -2,6 +2,7 @@
 import pickle
 import re
 import unittest
+from unittest import mock
 
 import pyfakefs.fake_filesystem_unittest as ffs
 from test.support import os_helper
@@ -168,6 +169,38 @@ def test_missing_metadata(self):
         with self.assertRaises(MetadataNotFound):
             metadata('foo')
 
+    def test_entry_points_prefer_valid_distribution(self):
+        """
+        Entry points should be exposed from the valid distribution when an
+        empty dist-info directory for the same name is discovered first.
+
+        Ref python/importlib_metadata#534.
+        """
+        fixtures.build_files(self.make_pkg('foo-0.9', files={}), self.site_dir)
+        fixtures.build_files(
+            self.make_pkg(
+                'foo-1.0',
+                files={
+                    "METADATA": """
+                    Name: foo
+                    Version: 1.0
+                    """,
+                    "entry_points.txt": """
+                    [entries]
+                    main = mod:main
+                    """,
+                },
+            ),
+            self.site_dir,
+        )
+        dists = [
+            Distribution.at(self.site_dir / 'foo-0.9.dist-info'),
+            Distribution.at(self.site_dir / 'foo-1.0.dist-info'),
+        ]
+        with mock.patch.object(importlib_metadata, 'distributions', return_value=dists):
+            entries = importlib_metadata.entry_points(group='entries')
+        assert entries['main'].value == 'mod:main'
+
 
 class NonASCIITests(fixtures.OnSysPath, fixtures.SiteDir, unittest.TestCase):
     @staticmethod