On Tue, Dec 21, 2021 at 4:20 PM Dmitry Gutov <dgutov@yandex.ru> wrote:

> > I'm okay with doing that  provided that the patch to revert is simple
and safe.  Please show the patch.
> I think I will let Joao take point on that.

It would seem that the right thing to do is to keep 26.1 dep
and do what Guillaume Pasquet suggests:

"or substitute the `string-replace` call with `replace-regexp-in-string` to
maintain compatibility as I have done here:

https://github.com/Etenil/flymake/commit/9f5f76907b1c258645f65728dd71e7cacffe6d22
"

> Note that the Package-Requires header in emacs-28 doesn't matter much.
> The problem will arise when that change is merged to master and then
> (sometime later) the Version header is also bumped in flymake.el.

Yup, yes this is indeed a problem.  That's why "core packages" have
this warning:

;; This is a GNU ELPA :core package.  Avoid functionality that is not
;; compatible with the version of Emacs recorded above.

(the version recorded above being 26.1) So whoever added string-replace
violated that. It might have been me, didn't check, but I don't think so.

Unfortunately, I don't have great solution for avoiding these kinds
of problems in the future.  An automatic test of `flymake.el` in Emacs
the recorded 26.1 could have picked this up. But we don't have them
and it's not super-easy to setup either.

I can only say that :core packages are a very good thing and
a way for users to get updates to fundamental packages
without waiting for the next major.

HTH,
João