bug#65414: save-some-buffers-functions are unexpectedly called when save-some-buffers pred is non-nil

[Eli Zaretskii <eliz@gnu.org>]

> From: Joseph Turner <joseph@breatheoutbreathe.in>
> Cc: 65414@debbugs.gnu.org, jonas@bernoul.li
> Date: Fri, 25 Aug 2023 23:38:18 -0700
> 
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Why is it undesirable?  save-some-buffers always saved abbrevs, didn't
> > it?  And it did so independently of PRED, right?  So how did this
> > problem suddenly started affecting Magit?
> >
> > IOW, I still don't have a clear idea what caused this problem, if
> > (AFAIU) it is a problem that started happening recently.
> 
> This problem is not new. However, now that save-some-buffers-functions
> has been added, the problem goes beyond abbrevs.
> 
> >> Another example: hyperdrive.el adds to save-some-buffers-functions for
> >> saving hyperdrive file buffers:
> >>
> >> https://git.sr.ht/~ushin/hyperdrive.el/tree/d7dc7a08ba47761108cf98e21ffa2d8dad28f34a/item/hyperdrive.el#L99
> >>
> >> After this change, magit-save-repository-buffers now prompts to save
> >> irrelevant hyperdrive file buffers. I would like some way to tell
> >> hyperdrive--save-some-buffers not to prompt the user to save hyperdrive
> >> buffers from inside magit-save-repository-buffers.
> >
> > Why do you want to do that?  Whether or not to prompt the user abides
> > by the common protocol defined by save-some-buffers: if it's called
> > with the argument ARG non-nil (which should happen interactively when
> > the user invokes the command with a prefix argument), there's no
> > prompt, otherwise Emacs prompts.  Why magit-save-repository-buffers
> > wants to break this common protocol?
> 
> I think magit-save-repository-buffers follows the common protocol
> correctly.
> 
> > I feel that I'm still missing something important, which causes you to
> > want a different behavior from magit-save-repository-buffers.  For
> > starters, can you describe how magit-save-repository-buffers ends up
> > calling save-some-buffers-functions in enough detail for me to
> > understand why you think saving these buffers is deemed "undesirable"?
> 
> The issue is not that save-some-buffers prompts instead of saving
> without questions.
> 
> What is undesirable to me is that save-some-buffers unconditionally
> calls each one of save-some-buffers-functions, regardless of PRED. This
> means that when save-some-buffers is used with the intention to save
> only a handful of files (as with magit-save-repository-buffers),
> save-some-buffers-functions are all called, even when irrelevant.

So your problem is with Lisp programs that add functions to
save-some-buffers-functions, but don't expect or don't want those
functions to be called each time save-some-buffers is invoked?

I'm not sure how did those Lisp programs get the idea that
save-some-buffers-functions will not be called always -- is it hinted
by some documentation somewhere?  If not, I'd say that those Lisp
programs have a bug that needs to be fixed in those programs.  Right?

In any case, not calling save-some-buffers-functions when PRED is
non-nil is not something we can do, as that would be an incompatible
behavior change.  We could perhaps add PRED to the arguments with
which save-some-buffers-functions are called, as an optional argument.
Would that be satisfactory?