bpo-44246: Restore compatibility in entry_points

Lib/importlib/metadata/__init__.py

@@ -204,7 +204,100 @@ def matches(self, **params):
         return all(map(operator.eq, params.values(), attrs))
 
 
-class EntryPoints(tuple):
+class DeprecatedList(list):
+    """
+    Allow an otherwise immutable object to implement mutability
+    for compatibility.
+
+    >>> recwarn = getfixture('recwarn')
+    >>> dl = DeprecatedList(range(3))
+    >>> dl[0] = 1
+    >>> dl.append(3)
+    >>> del dl[3]
+    >>> dl.reverse()
+    >>> dl.sort()
+    >>> dl.extend([4])
+    >>> dl.pop(-1)
+    4
+    >>> dl.remove(1)
+    >>> dl += [5]
+    >>> dl + [6]
+    [1, 2, 5, 6]
+    >>> dl + (6,)
+    [1, 2, 5, 6]
+    >>> dl.insert(0, 0)
+    >>> dl
+    [0, 1, 2, 5]
+    >>> dl == [0, 1, 2, 5]
+    True
+    >>> dl == (0, 1, 2, 5)
+    True
+    >>> len(recwarn)
+    1
+    """
+
+    _warn = functools.partial(
+        warnings.warn,
+        "EntryPoints list interface is deprecated. Cast to list if needed.",
+        DeprecationWarning,
+        stacklevel=2,
+    )
+
+    def __setitem__(self, *args, **kwargs):
+        self._warn()
+        return super().__setitem__(*args, **kwargs)
+
+    def __delitem__(self, *args, **kwargs):
+        self._warn()
+        return super().__delitem__(*args, **kwargs)
+
+    def append(self, *args, **kwargs):
+        self._warn()
+        return super().append(*args, **kwargs)
+
+    def reverse(self, *args, **kwargs):
+        self._warn()
+        return super().reverse(*args, **kwargs)
+
+    def extend(self, *args, **kwargs):
+        self._warn()
+        return super().extend(*args, **kwargs)
+
+    def pop(self, *args, **kwargs):
+        self._warn()
+        return super().pop(*args, **kwargs)
+
+    def remove(self, *args, **kwargs):
+        self._warn()
+        return super().remove(*args, **kwargs)
+
+    def __iadd__(self, *args, **kwargs):
+        self._warn()
+        return super().__iadd__(*args, **kwargs)
+
+    def __add__(self, other):
+        if not isinstance(other, tuple):
+            self._warn()
+            other = tuple(other)
+        return self.__class__(tuple(self) + other)
+
+    def insert(self, *args, **kwargs):
+        self._warn()
+        return super().insert(*args, **kwargs)
+
+    def sort(self, *args, **kwargs):
+        self._warn()
+        return super().sort(*args, **kwargs)
+
+    def __eq__(self, other):
+        if not isinstance(other, tuple):
+            self._warn()
+            other = tuple(other)
+
+        return tuple(self).__eq__(other)
+
+
+class EntryPoints(DeprecatedList):
     """
     An immutable collection of selectable EntryPoint objects.
     """
@@ -215,6 +308,14 @@ def __getitem__(self, name):  # -> EntryPoint:
         """
         Get the EntryPoint in self matching name.
         """
+        if isinstance(name, int):
+            warnings.warn(
+                "Accessing entry points by index is deprecated. "
+                "Cast to tuple if needed.",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+            return super().__getitem__(name)
         try:
             return next(iter(self.select(name=name)))
         except StopIteration:
@@ -493,6 +594,11 @@ def name(self):
         """Return the 'Name' metadata for the distribution package."""
         return self.metadata['Name']
 
+    @property
+    def _normalized_name(self):
+        """Return a normalized version of the name."""
+        return Prepared.normalize(self.name)
+
     @property
     def version(self):
         """Return the 'Version' metadata for the distribution package."""
@@ -795,6 +901,22 @@ def read_text(self, filename):
     def locate_file(self, path):
         return self._path.parent / path
 
+    @property
+    def _normalized_name(self):
+        """
+        Performance optimization: where possible, resolve the
+        normalized name from the file system path.
+        """
+        stem = os.path.basename(str(self._path))
+        return self._name_from_stem(stem) or super()._normalized_name
+
+    def _name_from_stem(self, stem):
+        name, ext = os.path.splitext(stem)
+        if ext not in ('.dist-info', '.egg-info'):
+            return
+        name, sep, rest = stem.partition('-')
+        return name
+
 
 def distribution(distribution_name):
     """Get the ``Distribution`` instance for the named package.
@@ -849,7 +971,8 @@ def entry_points(**params) -> Union[EntryPoints, SelectableGroups]:
 
     :return: EntryPoints or SelectableGroups for all installed packages.
     """
-    unique = functools.partial(unique_everseen, key=operator.attrgetter('name'))
+    norm_name = operator.attrgetter('_normalized_name')
+    unique = functools.partial(unique_everseen, key=norm_name)
     eps = itertools.chain.from_iterable(
         dist.entry_points for dist in unique(distributions())
     )

Lib/test/test_importlib/test_metadata_api.py

@@ -130,6 +130,22 @@ def test_entry_points_dict_construction(self):
         assert expected.category is DeprecationWarning
         assert "Construction of dict of EntryPoints is deprecated" in str(expected)
 
+    def test_entry_points_by_index(self):
+        """
+        Prior versions of Distribution.entry_points would return a
+        tuple that allowed access by index.
+        Capture this now deprecated use-case
+        See python/importlib_metadata#300 and bpo-44246.
+        """
+        eps = distribution('distinfo-pkg').entry_points
+        with warnings.catch_warnings(record=True) as caught:
+            eps[0]
+
+        # check warning
+        expected = next(iter(caught))
+        assert expected.category is DeprecationWarning
+        assert "Accessing entry points by index is deprecated" in str(expected)
+
     def test_entry_points_groups_getitem(self):
         # Prior versions of entry_points() returned a dict. Ensure
         # that callers using '.__getitem__()' are supported but warned to

Lib/test/test_importlib/test_zip.py

@@ -76,3 +76,7 @@ def test_files(self):
         for file in files('example'):
             path = str(file.dist.locate_file(file))
             assert '.egg/' in path, path
+
+    def test_normalized_name(self):
+        dist = distribution('example')
+        assert dist._normalized_name == 'example'

Misc/NEWS.d/next/Library/2021-05-31-11-28-03.bpo-44246.nhmt-v.rst

@@ -0,0 +1,3 @@
+In importlib.metadata.entry_points, de-duplication of distributions no
+longer requires loading the full metadata for PathDistribution objects,
+improving entry point loading performance by ~10x.

Misc/NEWS.d/next/Library/2021-05-31-11-34-56.bpo-44246.yHAkF0.rst

@@ -0,0 +1,7 @@
+In ``importlib.metadata``, restore compatibility in the result from
+``Distribution.entry_points`` (``EntryPoints``) to honor expectations in
+older implementations and issuing deprecation warnings for these cases: A. ``EntryPoints`` objects are once again mutable, allowing   for ``sort()``
+and other list-based mutation operations.   Avoid deprecation warnings by
+casting to a   mutable sequence (e.g.   ``list(dist.entry_points).sort()``). B. ``EntryPoints`` results once again allow   for access by index. To avoid
+deprecation warnings,   cast the result to a Sequence first   (e.g.
+``tuple(dist.entry_points)[0]``).