Track dependency categories on recursive dependencies

When enumerating the recursive dependencies for a package descriptor,
track which dependency categories the dependency appears to be a part
of. This information can be used later to drop certain dependencies or
inform a developer of the context around a relationship.

colcon_core/package_descriptor.py

@@ -71,16 +71,20 @@ def get_dependencies(self, *, categories=None):
  :raises AssertionError: if the package name is listed as a dependency
  """
  dependencies = set()
+ categories_by_dependency = defaultdict(list)
  if categories is None:
  categories = self.dependencies.keys()
  for category in sorted(categories):
- dependencies |= self.dependencies[category]
+ for dependency in self.dependencies[category]:
+ categories_by_dependency[dependency].append(category)
+ for dependency, categories in categories_by_dependency.items():
+ if not isinstance(dependency, DependencyDescriptor):
+ dependency = DependencyDescriptor(dependency)
+ dependency.metadata['categories'] = categories
+ dependencies.add(dependency)
  assert self.name not in dependencies, \
  f"The package '{self.name}' has a dependency with the same name"
- return {
- (DependencyDescriptor(d)
- if not isinstance(d, DependencyDescriptor) else d)
- for d in dependencies}
+ return dependencies
 
  def get_recursive_dependencies(
  self, descriptors, direct_categories=None, recursive_categories=None,