Fix entry point discovery on Python < 3.10

It seems that the behavior of the importlib.metadata.entry_points
function changed in Python 3.10 to automatically de-duplicate
distributions, but prior to that the "shadowed" distributions were also
enumerated. This change specifically ignores "shadowed" distributions so
that they aren't identified as extension point overwrites.

colcon_core/extension_point.py

@@ -37,6 +37,15 @@
 EXTENSION_POINT_GROUP_NAME = 'colcon_core.extension_point'
 
 
+def _get_unique_distributions():
+ seen = set()
+ for dist in distributions():
+ dist_name = dist.metadata['Name']
+ if dist_name not in seen:
+ seen.add(dist_name)
+ yield dist
+
+
 def get_all_extension_points():
  """
  Get all extension points related to `colcon` and any of its extensions.
@@ -51,12 +60,7 @@ def get_all_extension_points():
  colcon_extension_points.setdefault(EXTENSION_POINT_GROUP_NAME, None)
 
  entry_points = defaultdict(dict)
- seen = set()
- for dist in distributions():
- dist_name = dist.metadata['Name']
- if dist_name in seen:
- continue
- seen.add(dist_name)
+ for dist in _get_unique_distributions():
  for entry_point in dist.entry_points:
  # skip groups which are not registered as extension points
  if entry_point.group not in colcon_extension_points:
@@ -70,7 +74,7 @@ def get_all_extension_points():
  f"from '{dist._path}' "
  f"overwriting '{previous}'")
  entry_points[entry_point.group][entry_point.name] = \
- (entry_point.value, dist_name, dist.version)
+ (entry_point.value, dist.metadata['Name'], dist.version)
  return entry_points
 
 
@@ -87,7 +91,11 @@ def get_extension_points(group):
  # Python 3.10 and newer
  query = entry_points(group=group)
  except TypeError:
- query = entry_points().get(group, ())
+ query = (
+ entry_point
+ for dist in _get_unique_distributions()
+ for entry_point in dist.entry_points
+ if entry_point.group == group)
  for entry_point in query:
  if entry_point.name in extension_points:
  previous_entry_point = extension_points[entry_point.name]

test/test_extension_point.py

@@ -54,8 +54,8 @@ def iter_entry_points(*, group=None):
 
 def distributions():
  return [
- Dist(iter_entry_points(group='group1')),
- Dist([EntryPoint('extC', 'eC', Group2.name)]),
+ Dist([Group1, ExtA, ExtB]),
+ Dist([Group2, EntryPoint('extC', 'eC', Group2.name)]),
  Dist([EntryPoint('extD', 'eD', 'groupX')]),
  ]
 
@@ -71,7 +71,11 @@ def test_all_extension_points():
  ):
  # successfully load a known entry point
  extension_points = get_all_extension_points()
- assert set(extension_points.keys()) == {'group1', 'group2'}
+ assert set(extension_points.keys()) == {
+ EXTENSION_POINT_GROUP_NAME,
+ 'group1',
+ 'group2',
+ }
  assert set(extension_points['group1'].keys()) == {'extA', 'extB'}
  assert extension_points['group1']['extA'][0] == 'eA'