On Sat, Mar 25, 2023, 12:55 Eli Zaretskii <eliz@gnu.org> wrote:.

>
> So it is most clearly a regression.

There's something missing in the above description, since
buffer-match-p accepts a function as its CONDITION argument, and calls
that function with the buffer and ACTION. So it sounds like code
written for Emacs 28 should still work. What is missing here that
explains the breakage?

As I highlighted, Emacs used to call such functions with a buffer _name_ and an action. Now it calls them with a buffer _object_ and an action. This is a backward-incompatible change.

João