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

[Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Joseph Turner <joseph@breatheoutbreathe.in>
>> Cc: 65414@debbugs.gnu.org, jonas@bernoul.li
>> Date: Wed, 23 Aug 2023 16:57:06 -0700
>>
>> magit-save-repository-buffers docstring reads "Save file-visiting
>> buffers belonging to the current repository." IIUC, prompting to save
>> abbrevs here is an undesirable implementation side-effect.
>
> 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.

Thanks again for your patience :)

Joseph