Merge pull request #397 from abravalheri/issue-396

Add compatibility for `PathDistributions` implemented with stdlib objects in Python 3.8/3.9

.github/workflows/main.yml

@@ -20,6 +20,10 @@ jobs:
         include:
         - python: pypy3.9
           platform: ubuntu-latest
+        - platform: ubuntu-latest
+          python: "3.8"
+        - platform: ubuntu-latest
+          python: "3.9"
     runs-on: ${{ matrix.platform }}
     steps:
       - uses: actions/checkout@v3

CHANGES.rst

@@ -1,3 +1,9 @@
+v4.13.0
+=======
+
+* #396: Added compatibility for ``PathDistributions`` originating
+  from Python 3.8 and 3.9.
+
 v4.12.0
 =======
 

importlib_metadata/__init__.py

@@ -14,7 +14,7 @@
 import posixpath
 import collections
 
-from . import _adapters, _meta
+from . import _adapters, _meta, _py39compat
 from ._collections import FreezableDefaultDict, Pair
 from ._compat import (
     NullFinder,
@@ -189,6 +189,10 @@ class EntryPoint(DeprecatedTuple):
     following the attr, and following any extras.
     """
 
+    name: str
+    value: str
+    group: str
+
     dist: Optional['Distribution'] = None
 
     def __init__(self, name, value, group):
@@ -378,7 +382,8 @@ def select(self, **params):
         Select entry points from self that match the
         given parameters (typically group and/or name).
         """
-        return EntryPoints(ep for ep in self if ep.matches(**params))
+        candidates = (_py39compat.ep_matches(ep, **params) for ep in self)
+        return EntryPoints(ep for ep, predicate in candidates if predicate)
 
     @property
     def names(self):
@@ -1017,7 +1022,7 @@ def version(distribution_name):
 
 _unique = functools.partial(
     unique_everseen,
-    key=operator.attrgetter('_normalized_name'),
+    key=_py39compat.normalized_name,
 )
 """
 Wrapper for ``distributions`` to return unique distributions by name.

importlib_metadata/_py39compat.py

@@ -0,0 +1,48 @@
+"""
+Compatibility layer with Python 3.8/3.9
+"""
+from typing import TYPE_CHECKING, Any, Optional, Tuple
+
+if TYPE_CHECKING:  # pragma: no cover
+    # Prevent circular imports on runtime.
+    from . import Distribution, EntryPoint
+else:
+    Distribution = EntryPoint = Any
+
+
+def normalized_name(dist: Distribution) -> Optional[str]:
+    """
+    Honor name normalization for distributions that don't provide ``_normalized_name``.
+    """
+    try:
+        return dist._normalized_name
+    except AttributeError:
+        from . import Prepared  # -> delay to prevent circular imports.
+
+        return Prepared.normalize(getattr(dist, "name", None) or dist.metadata['Name'])
+
+
+def ep_matches(ep: EntryPoint, **params) -> Tuple[EntryPoint, bool]:
+    """
+    Workaround for ``EntryPoint`` objects without the ``matches`` method.
+    For the sake of convenience, a tuple is returned containing not only the
+    boolean value corresponding to the predicate evalutation, but also a compatible
+    ``EntryPoint`` object that can be safely used at a later stage.
+
+    For example, the following sequences of expressions should be compatible:
+
+        # Sequence 1: using the compatibility layer
+        candidates = (_py39compat.ep_matches(ep, **params) for ep in entry_points)
+        [ep for ep, predicate in candidates if predicate]
+
+        # Sequence 2: using Python 3.9+
+        [ep for ep in entry_points if ep.matches(**params)]
+    """
+    try:
+        return ep, ep.matches(**params)
+    except AttributeError:
+        from . import EntryPoint  # -> delay to prevent circular imports.
+
+        # Reconstruct the EntryPoint object to make sure it is compatible.
+        _ep = EntryPoint(ep.name, ep.value, ep.group)
+        return _ep, _ep.matches(**params)

tests/test_py39compat.py

@@ -0,0 +1,74 @@
+import sys
+import pathlib
+import unittest
+
+from . import fixtures
+from importlib_metadata import (
+    distribution,
+    distributions,
+    entry_points,
+    metadata,
+    version,
+)
+
+
+class OldStdlibFinderTests(fixtures.DistInfoPkgOffPath, unittest.TestCase):
+    def setUp(self):
+        python_version = sys.version_info[:2]
+        if python_version < (3, 8) or python_version > (3, 9):
+            self.skipTest("Tests specific for Python 3.8/3.9")
+        super().setUp()
+
+    def _meta_path_finder(self):
+        from importlib.metadata import (
+            Distribution,
+            DistributionFinder,
+            PathDistribution,
+        )
+        from importlib.util import spec_from_file_location
+
+        path = pathlib.Path(self.site_dir)
+
+        class CustomDistribution(Distribution):
+            def __init__(self, name, path):
+                self.name = name
+                self._path_distribution = PathDistribution(path)
+
+            def read_text(self, filename):
+                return self._path_distribution.read_text(filename)
+
+            def locate_file(self, path):
+                return self._path_distribution.locate_file(path)
+
+        class CustomFinder:
+            @classmethod
+            def find_spec(cls, fullname, _path=None, _target=None):
+                candidate = pathlib.Path(path, *fullname.split(".")).with_suffix(".py")
+                if candidate.exists():
+                    return spec_from_file_location(fullname, candidate)
+
+            @classmethod
+            def find_distributions(self, context=DistributionFinder.Context()):
+                for dist_info in path.glob("*.dist-info"):
+                    yield PathDistribution(dist_info)
+                    name, _, _ = str(dist_info).partition("-")
+                    yield CustomDistribution(name + "_custom", dist_info)
+
+        return CustomFinder
+
+    def test_compatibility_with_old_stdlib_path_distribution(self):
+        """
+        Given a custom finder that uses Python 3.8/3.9 importlib.metadata is installed,
+        when importlib_metadata functions are called, there should be no exceptions.
+        Ref python/importlib_metadata#396.
+        """
+        self.fixtures.enter_context(fixtures.install_finder(self._meta_path_finder()))
+
+        assert list(distributions())
+        assert distribution("distinfo_pkg")
+        assert distribution("distinfo_pkg_custom")
+        assert version("distinfo_pkg") > "0"
+        assert version("distinfo_pkg_custom") > "0"
+        assert list(metadata("distinfo_pkg"))
+        assert list(metadata("distinfo_pkg_custom"))
+        assert list(entry_points(group="entries"))