Update pkg_resources's default distribution metadata object.

`pkg_resources` creates a default WorkingSet as soon as it is
imported, so even though we add hooks for it to find the .dist-info
metadata inside .par files, it is too late.  So we manually update the
default WorkingSet, trying not to disturb existing entries.

runtime/support.py

@@ -33,8 +33,10 @@
 """
 
 import os
+import pkgutil
 import sys
 import warnings
+import zipimport
 
 
 def _log(msg):
@@ -61,10 +63,21 @@ def _find_archive():
     return archive_path
 
 
-def _setup_pkg_resources():
+def _setup_pkg_resources(pkg_resources_name):
+    """Setup hooks into the `pkg_resources` module
+
+    This enables the pkg_resources module to find metadata from wheels
+    that have been included in this .par file.
+
+    The functions and classes here are scoped to this function, since
+    we might have multitple pkg_resources modules, or none.
+    """
+
     try:
-        import pkg_resources
-        import zipimport
+        __import__(pkg_resources_name)
+        pkg_resources = sys.modules.get(pkg_resources_name)
+        if pkg_resources is None:
+            return
     except ImportError:
         # Skip setup
         return
@@ -125,17 +138,20 @@ def find_eggs_and_dist_info_in_zip(importer, path_item, only=False):
             yield dist
         return
 
-
     # This overwrites the existing registered finder.
-    #
-    # Note that this also doesn't update the default WorkingSet created by
-    # pkg_resources when it is imported, since there is no public
-    # interface to do so that doesn't also have a "Don't use this"
-    # warning.
     pkg_resources.register_finder(zipimport.zipimporter,
                                   find_eggs_and_dist_info_in_zip)
 
-
+    # Note that the default WorkingSet has already been created, and
+    # there is no public interface to easily refresh/reload it that
+    # doesn't also have a "Don't use this" warning.  So we manually
+    # add just the entries we know about to the existing WorkingSet.
+    for entry in sys.path:
+        importer = pkgutil.get_importer(entry)
+        if isinstance(importer, zipimport.zipimporter):
+            for dist in find_dist_info_in_zip(importer, entry, only=True):
+                pkg_resources.working_set.add(dist, entry, insert=False,
+                                              replace=False)
 
 
 def setup(import_roots=None):
@@ -154,4 +170,5 @@ def setup(import_roots=None):
         sys.path.insert(1, new_path)
 
     # Add hook for package metadata
-    _setup_pkg_resources()
+    _setup_pkg_resources('pkg_resources')
+    _setup_pkg_resources('pip._vendor.pkg_resources')

runtime/support_test.py

@@ -21,7 +21,7 @@
 
 class SupportTest(unittest.TestCase):
 
-    def test_log(self):
+    def test__log(self):
         old_stderr = sys.stderr
         try:
             mock_stderr = io.StringIO()
@@ -36,17 +36,34 @@ def test_log(self):
         finally:
             sys.stderr = old_stderr
 
-    def test_find_archive(self):
+    def test__find_archive(self):
         # pylint: disable=protected-access
         path = support._find_archive()
         self.assertNotEqual(path, None)
 
     def test_setup(self):
-        support.setup(import_roots=['some_root', 'another_root'])
-        self.assertTrue(sys.path[1].endswith('subpar/runtime/some_root'),
-                        sys.path)
-        self.assertTrue(sys.path[2].endswith('subpar/runtime/another_root'),
-                        sys.path)
+        # `import pip` can cause arbitrary sys.path changes,
+        # especially if using the Debian `python-pip` package or
+        # similar.  Get that lunacy out of the way before starting
+        # test
+        try:
+            import pip
+        except ImportError:
+            pass
+
+        old_sys_path = sys.path
+        try:
+            mock_sys_path = list(sys.path)
+            sys.path = mock_sys_path
+            support.setup(import_roots=['some_root', 'another_root'])
+        finally:
+            sys.path = old_sys_path
+        self.assertTrue(mock_sys_path[1].endswith('subpar/runtime/some_root'),
+                        mock_sys_path)
+        self.assertTrue(mock_sys_path[2].endswith('subpar/runtime/another_root'),
+                        mock_sys_path)
+        self.assertEqual(mock_sys_path[0], sys.path[0])
+        self.assertEqual(mock_sys_path[3:], sys.path[1:])
 
 
 if __name__ == '__main__':

tests/package_pkg_resources/main.py

@@ -26,7 +26,7 @@ def main():
         print('Skipping test, pkg_resources module is not available')
         return
 
-    ws = pkg_resources.WorkingSet()
+    ws = pkg_resources.working_set
 
     # Informational for debugging
     distributions = list(ws)