bug#47286: 28.0.50; [PATCH] Replace "(default %s)" with 'format-prompt'

[Gabriel]

Kévin Le Gouguec <kevin.legouguec@gmail.com> writes:
>
> Mmm, project.el is released on ELPA as a :core package; IIUC it strives
> for backward-compatibility as far back as Emacs 26.1
> (cf. Package-Requires field at the top of the file), so maybe it's a bit
> early to use format-prompt there?
>
> Apologies if I'm misunderstanding something.

Hi Kevin,

Thanks for pointing it out. I just searched for the current source tree
of master branch for ocurrences of "(default %s)", so I am not sure if I
changed some package that shouldn't be update. If so, I will promptly
update the patch.

Perhaps project.el could use a similar fallback that exists on
cperl-mode.el (commit 3a95f4fc12df0a570ad413e099a22bf901b7346d):

;; Available in Emacs 28: format-prompt
(defalias 'cperl--format-prompt
  (if (fboundp 'format-prompt) 'format-prompt
    (lambda (msg default)
      (if default (format "%s (default %s): " msg default)
        (concat msg ": ")))))