always process module.__path__ for namespace packages, fixes #1321

pkg_resources/__init__.py

@@ -2135,12 +2135,13 @@ def _rebuild_mod_path(orig_path, package_name, module):
         parts = path_parts[:-module_parts]
         return safe_sys_path_index(_normalize_cached(os.sep.join(parts)))
 
-    if not isinstance(orig_path, list):
-        # Is this behavior useful when module.__path__ is not a list?
-        return
+    new_path = sorted(orig_path, key=position_in_sys_path)
+    new_path = [_normalize_cached(p) for p in new_path]
 
-    orig_path.sort(key=position_in_sys_path)
-    module.__path__[:] = [_normalize_cached(p) for p in orig_path]
+    if isinstance(module.__path__, list):
+        module.__path__[:] = new_path
+    else:
+        module.__path__ = new_path
 
 
 def declare_namespace(packageName):

setuptools/tests/test_namespaces.py

@@ -109,3 +109,34 @@ class TestNamespaces:
         ]
         with test.test.paths_on_pythonpath([str(target)]):
             subprocess.check_call(pkg_resources_imp, cwd=str(pkg_A))
+
+    @pytest.mark.skipif(bool(os.environ.get("APPVEYOR")),
+        reason="https://github.com/pypa/setuptools/issues/851")
+    def test_packages_in_the_sampe_namespace_installed_and_cwd(self, tmpdir):
+        """
+        Installing one namespace package and also have another in the same
+        namespace in the current working directory, both of them must be
+        importable.
+        """
+        pkg_A = namespaces.build_namespace_package(tmpdir, 'myns.pkgA')
+        pkg_B = namespaces.build_namespace_package(tmpdir, 'myns.pkgB')
+        target = tmpdir / 'packages'
+        # use pip to install to the target directory
+        install_cmd = [
+            sys.executable,
+            '-m',
+            'pip.__main__',
+            'install',
+            str(pkg_A),
+            '-t', str(target),
+        ]
+        subprocess.check_call(install_cmd)
+        namespaces.make_site_dir(target)
+
+        # ensure that all packages import and pkg_resources imports
+        pkg_resources_imp = [
+            sys.executable,
+            '-c', 'import pkg_resources; import myns.pkgA; import myns.pkgB',
+        ]
+        with test.test.paths_on_pythonpath([str(target)]):
+            subprocess.check_call(pkg_resources_imp, cwd=str(pkg_B))