Dmitry Gutov <dgutov@yandex.ru> writes:

> Yeah, so: what's the plan for Magit?
>
> Will the new version of it have to
>
> (if <emacs version is...>
>     (defface ...)
>   (defface ...)
>
> ?

> We should define and document a "migration path", e.g. say what a
> package author should do if they have a face which needs to be
> extended, preferably without breaking compatibility with Emacs 26.

Earlier in the thread[1] I suggested this method to avoid the duplicate
defface issue: