Add comments to {typing,_collections_abc}._type_repr about each other

Lib/_collections_abc.py

@@ -518,8 +518,9 @@ def _type_repr(obj):
     Copied from :mod:`typing` since collections.abc
     shouldn't depend on that module.
     """
-    if isinstance(obj, GenericAlias):
-        return repr(obj)
+    # When changing this function, don't forget about
+    # `typing._type_repr`, which does the same thing
+    # and must be consistent with this one.
     if isinstance(obj, type):
         if obj.__module__ == 'builtins':
             return obj.__qualname__

Lib/typing.py

@@ -230,6 +230,9 @@ def _type_repr(obj):
     typically enough to uniquely identify a type.  For everything
     else, we fall back on repr(obj).
     """
+    # When changing this function, don't forget about
+    # `_collections_abc._type_repr`, which does the same thing
+    # and must be consistent with this one.
     if isinstance(obj, type):
         if obj.__module__ == 'builtins':
             return obj.__qualname__