Fixes the original root cause of #231, and re-enables the test when the...

Fixes the original root cause of #231, and re-enables the test when the tempdir is a symlink (this does not explicitly test that /tmp itself is a symlink, but the effect is the same--only one of the path levels needs to be a symlink to reproduce this isssue)

pkg_resources/__init__.py

@@ -2182,9 +2182,14 @@ def _handle_ns(packageName, path_item):
         path = module.__path__
         path.append(subpath)
         loader.load_module(packageName)
+
+        # Ensure that all paths on __path__ have been run through
+        # normalize_path
+        normalized_paths = set(_normalize_cached(p) for p in module.__path__)
         for path_item in path:
-            if path_item not in module.__path__:
-                module.__path__.append(path_item)
+            normalized = _normalize_cached(path_item)
+            if normalized not in normalized_paths:
+                module.__path__.append(normalized)
     return subpath
 
 def declare_namespace(packageName):

pkg_resources/tests/test_resources.py

@@ -610,18 +610,32 @@ class TestNamespaces:
 
     def setup_method(self, method):
         self._ns_pkgs = pkg_resources._namespace_packages.copy()
-        self._tmpdir = tempfile.mkdtemp(prefix="tests-setuptools-")
+
+        # Further, test case where the temp dir is a symlink, where applicable
+        # See #231
+        if hasattr(os, 'symlink'):
+            real_tmpdir = tempfile.mkdtemp(prefix="real-tests-setuptools-")
+            tmpdir_base, tmpdir_name = os.path.split(real_tmpdir)
+            tmpdir = os.path.join(tmpdir_base, tmpdir_name[5:])
+            os.symlink(real_tmpdir, tmpdir)
+            self._real_tmpdir = real_tmpdir
+            self._tmpdir = tmpdir
+        else:
+            tmpdir = tempfile.mkdtemp(prefix="tests-setuptools-")
+            self._real_tmpdir = self._tmpdir = tmpdir
+
         os.makedirs(os.path.join(self._tmpdir, "site-pkgs"))
         self._prev_sys_path = sys.path[:]
         sys.path.append(os.path.join(self._tmpdir, "site-pkgs"))
 
     def teardown_method(self, method):
-        shutil.rmtree(self._tmpdir)
+        shutil.rmtree(self._real_tmpdir)
+        if os.path.islink(self._tmpdir):
+            os.unlink(self._tmpdir)
+
         pkg_resources._namespace_packages = self._ns_pkgs.copy()
         sys.path = self._prev_sys_path[:]
 
-    @pytest.mark.skipif(os.path.islink(tempfile.gettempdir()),
-        reason="Test fails when /tmp is a symlink. See #231")
     def test_two_levels_deep(self):
         """
         Test nested namespace packages
@@ -653,7 +667,7 @@ class TestNamespaces:
         assert pkg_resources._namespace_packages["pkg1"] == ["pkg1.pkg2"]
         # check the __path__ attribute contains both paths
         expected = [
-            os.path.join(self._tmpdir, "site-pkgs", "pkg1", "pkg2"),
-            os.path.join(self._tmpdir, "site-pkgs2", "pkg1", "pkg2"),
+            os.path.join(self._real_tmpdir, "site-pkgs", "pkg1", "pkg2"),
+            os.path.join(self._real_tmpdir, "site-pkgs2", "pkg1", "pkg2"),
         ]
         assert pkg1.pkg2.__path__ == expected