gh-84530: fix namespace package support in modulefinder

Lib/importlib/_bootstrap.py

@@ -752,17 +752,18 @@ def _init_module_attrs(spec, module, *, override=False):
                 loader = NamespaceLoader.__new__(NamespaceLoader)
                 loader._path = spec.submodule_search_locations
                 spec.loader = loader
-                # While the docs say that module.__file__ is not set for
-                # built-in modules, and the code below will avoid setting it if
-                # spec.has_location is false, this is incorrect for namespace
-                # packages.  Namespace packages have no location, but their
-                # __spec__.origin is None, and thus their module.__file__
-                # should also be None for consistency.  While a bit of a hack,
-                # this is the best place to ensure this consistency.
-                #
-                # See # https://docs.python.org/3/library/importlib.html#importlib.abc.Loader.load_module
-                # and bpo-32305
-                module.__file__ = None
+        if _bootstrap_external and isinstance(loader, _bootstrap_external.NamespaceLoader):
+            # While the docs say that module.__file__ is not set for
+            # built-in modules, and the code below will avoid setting it if
+            # spec.has_location is false, this is incorrect for namespace
+            # packages.  Namespace packages have no location, but their
+            # __spec__.origin is None, and thus their module.__file__
+            # should also be None for consistency.  While a bit of a hack,
+            # this is the best place to ensure this consistency.
+            #
+            # See # https://docs.python.org/3/library/importlib.html#importlib.abc.Loader.load_module
+            # and bpo-32305
+            module.__file__ = None
         try:
             module.__loader__ = loader
         except AttributeError:

Lib/importlib/_bootstrap_external.py

@@ -1296,6 +1296,7 @@ def find_spec(cls, fullname, path=None, target=None):
                 # can create the namespace package.
                 spec.origin = None
                 spec.submodule_search_locations = _NamespacePath(fullname, namespace_path, cls._get_spec)
+                spec.loader = NamespaceLoader(fullname, namespace_path, cls._get_spec)
                 return spec
             else:
                 return None

Lib/modulefinder.py

@@ -17,6 +17,7 @@
 _PKG_DIRECTORY = 5
 _C_BUILTIN = 6
 _PY_FROZEN = 7
+_NAMESPACE = 8
 
 # Modulefinder does a good job at simulating Python's, but it can not
 # handle __path__ modifications packages make at runtime.  Therefore there
@@ -66,7 +67,10 @@ def _find_module(name, path=None):
 
     file_path = spec.origin
 
-    if spec.loader.is_package(name):
+    if isinstance(spec.loader, importlib.machinery.NamespaceLoader):
+        return None, spec.submodule_search_locations, ("", "", _NAMESPACE)
+
+    if spec.loader.is_package(name):  # non-namespace package
         return None, os.path.dirname(file_path), ("", "", _PKG_DIRECTORY)
 
     if isinstance(spec.loader, importlib.machinery.SourceFileLoader):

Lib/test/test_modulefinder.py

@@ -76,6 +76,18 @@
                                 from sys import version_info
 """]
 
+namespace_package_test = [
+    "module",
+    ["a", "module"],
+    ["a.c", "blahblah"], [],
+    """\
+module.py
+                                import a
+                                import a.c
+                                import blahblah
+a/b.py
+"""]
+
 absolute_import_test = [
     "a.module",
     ["a", "a.module",
@@ -353,6 +365,9 @@ def _do_test(self, info, report=False, debug=0, replace_paths=[], modulefinder_c
     def test_package(self):
         self._do_test(package_test)
 
+    def test_namespace_package(self):
+        self._do_test(namespace_package_test)
+
     def test_maybe(self):
         self._do_test(maybe_test)
 

Misc/NEWS.d/next/Library/2021-10-23-22-12-13.bpo-40350.t0dQMY.rst

@@ -0,0 +1 @@
+Fix support for namespace packages in :mod:`modulefinder`.