add som notes

src/python/pants/backend/python/tasks/build_local_python_distributions.py

@@ -65,7 +65,7 @@ def _setup_py_native_tools(self):
     native_toolchain = NativeToolchain.scoped_instance(self)
     return self._request_single(SetupPyNativeTools, native_toolchain)
 
-  # TODO: This should probably be made into a class property, when that is made.
+  # TODO: This should probably be made into an @classproperty (see PR #5901).
   @property
   def cache_target_dirs(self):
     return True

src/python/pants/util/objects.py

@@ -313,12 +313,14 @@ def satisfied_by_type(self, obj_type):
 
 class Collection(object):
   """Constructs classes representing collections of objects of a particular type."""
+  # TODO: could we check that the input is iterable in the ctor?
 
   @classmethod
   @memoized
   def of(cls, *element_types):
     union = '|'.join(element_type.__name__ for element_type in element_types)
     type_name = b'{}.of({})'.format(cls.__name__, union)
+    # TODO: could we allow type checking in the datatype() invocation here?
     supertypes = (cls, datatype(['dependencies'], superclass_name='Collection'))
     properties = {'element_types': element_types}
     collection_of_type = type(type_name, supertypes, properties)