bug#69584: 29.2.50; project-find-functions should have access to maybe-prompt

[Spencer Baugh <sbaugh@janestreet.com>]

Spencer Baugh <sbaugh@janestreet.com> writes:
> So when you open up a branch overview, you'll usually assume there's a
> local copy, and so your first action will probably some command which
> uses project-current.  But if there's no working copy, then you'll get
> dropped to a prompt to choose a project, instead of (say) a
> project-find-file prompt, which you might not immediately notice, which
> is confusing, and you'll have to C-g out of it, and then run some other
> command to create the working copy.  All that is a hassle.

Oh, I've thought of a different resolution to this which may be better.

When project-current fails to find a project in default-directory, if
maybe-prompt=t, project-current will run project-prompter.

So I can just have a buffer-local project-prompter in the branch
overview buffer.  And that project-prompter knows it's in a branch
overview buffer, and can prompt "Would you like to make a working copy
for [some branch]?".

That's elegant and doesn't change the semantics of project-current at
all: project-prompter already can return an arbitrary directory.

Except... I suppose this would make project-switch-project behave worse,
because hitting C-x p p in a branch overview buffer would now prompt to
create a working copy for that branch, when what you probably want to do
is switch to a different project entirely.

I guess there are two use cases for project-prompter: one is "fallback
for project-current" and the other is "switch to a different project".
Maybe we could support them being different?