--- a/mercurial/exthelper.py Thu Dec 27 00:10:40 2018 -0500
+++ b/mercurial/exthelper.py Sun Dec 23 14:52:43 2018 -0500
@@ -246,6 +246,15 @@
This function takes two arguments, the container and the name of the
function to wrap. The wrapping is performed during `uisetup`.
+ Adding attributes to a container like this is discouraged, because the
+ container modification is visible even in repositories that do not
+ have the extension loaded. Therefore, care must be taken that the
+ function doesn't make assumptions that the extension was loaded for the
+ current repository. For `ui` and `repo` instances, a better option is
+ to subclass the instance in `uipopulate` and `reposetup` respectively.
+
+ https://www.mercurial-scm.org/wiki/WritingExtensions
+
example::
@eh.addattr(context.changectx, 'babar')