Yes, the pg_commit_ts directory is not transferred by pg_upgrade.
Basically, you can get the exact same result by manually copying the
pg_commit_ts directory and running pg_resetwal. And this patch does it
automatically.
In other words, the patch provides the stated functionality, but
consider running pgindet.
I'm not sure whether there were any reasons not to make this move from
the beginning. The authors' opinions are needed here.
And one more thing. In my perspective, having some tests is always a
good idea, even if they are not meant to be committed. After briefly
examining the patch, I developed this basic test. This is not finalized
in any manner, but it is simply an idea.
-- Best regards,
Maxim Orlov.