Wrap .files call in always_iterable per recommendation

CHANGES.rst

@@ -1,3 +1,9 @@
+v4.7.1
+======
+
+* #344: Fixed regression in ``packages_distributions`` when
+  neither top-level.txt nor a files manifest is present.
+
 v4.7.0
 ======
 

importlib_metadata/__init__.py

@@ -23,7 +23,7 @@
     pypy_partial,
 )
 from ._functools import method_cache
-from ._itertools import unique_everseen
+from ._itertools import always_iterable, unique_everseen
 from ._meta import PackageMetadata, SimplePath
 
 from contextlib import suppress
@@ -1025,6 +1025,6 @@ def _top_level_declared(dist):
 def _top_level_inferred(dist):
     return {
         f.parts[0] if len(f.parts) > 1 else f.with_suffix('').name
-        for f in dist.files
+        for f in always_iterable(dist.files)
         if f.suffix == ".py"
     }

importlib_metadata/_itertools.py

@@ -17,3 +17,57 @@ def unique_everseen(iterable, key=None):
             if k not in seen:
                 seen_add(k)
                 yield element
+
+
+# copied from more_itertools 8.8
+def always_iterable(obj, base_type=(str, bytes)):
+    """If *obj* is iterable, return an iterator over its items::
+
+        >>> obj = (1, 2, 3)
+        >>> list(always_iterable(obj))
+        [1, 2, 3]
+
+    If *obj* is not iterable, return a one-item iterable containing *obj*::
+
+        >>> obj = 1
+        >>> list(always_iterable(obj))
+        [1]
+
+    If *obj* is ``None``, return an empty iterable:
+
+        >>> obj = None
+        >>> list(always_iterable(None))
+        []
+
+    By default, binary and text strings are not considered iterable::
+
+        >>> obj = 'foo'
+        >>> list(always_iterable(obj))
+        ['foo']
+
+    If *base_type* is set, objects for which ``isinstance(obj, base_type)``
+    returns ``True`` won't be considered iterable.
+
+        >>> obj = {'a': 1}
+        >>> list(always_iterable(obj))  # Iterate over the dict's keys
+        ['a']
+        >>> list(always_iterable(obj, base_type=dict))  # Treat dicts as a unit
+        [{'a': 1}]
+
+    Set *base_type* to ``None`` to avoid any special handling and treat objects
+    Python considers iterable as iterable:
+
+        >>> obj = 'foo'
+        >>> list(always_iterable(obj, base_type=None))
+        ['f', 'o', 'o']
+    """
+    if obj is None:
+        return iter(())
+
+    if (base_type is not None) and isinstance(obj, base_type):
+        return iter((obj,))
+
+    try:
+        return iter(obj)
+    except TypeError:
+        return iter((obj,))

tests/test_main.py

@@ -285,7 +285,7 @@ def test_unicode_dir_on_sys_path(self):
         list(distributions())
 
 
-class PackagesDistributionsTest(fixtures.ZipFixtures, unittest.TestCase):
+class PackagesDistributionsPrebuiltTest(fixtures.ZipFixtures, unittest.TestCase):
     def test_packages_distributions_example(self):
         self._fixture_on_path('example-21.12-py3-none-any.whl')
         assert packages_distributions()['example'] == ['example']
@@ -297,3 +297,24 @@ def test_packages_distributions_example2(self):
         """
         self._fixture_on_path('example2-1.0.0-py3-none-any.whl')
         assert packages_distributions()['example2'] == ['example2']
+
+
+class PackagesDistributionsTest(
+    fixtures.OnSysPath, fixtures.SiteDir, unittest.TestCase
+):
+    def test_packages_distributions_neither_toplevel_nor_files(self):
+        """
+        Test a package built without 'top-level.txt' or a file list.
+        """
+        fixtures.build_files(
+            {
+                'trim_example-1.0.0.dist-info': {
+                    'METADATA': """
+                Name: trim_example
+                Version: 1.0.0
+                """,
+                }
+            },
+            prefix=self.site_dir,
+        )
+        packages_distributions()