Given that in the 2 or so years that matchers are thing nobody complained,
it seems that people do not actually write this sort of code, and the
possibility will be removed in v3. However, to avoid correctness bugs,
we will have to support this weird code in v2.
This captures the intent better, as some changes are indeed plain
deprecations leading to removal, but other changes can be viewed
as minor tune-ups instead.
