Re: make pred customable in auto-save-visited-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Sat, 31 Mar 2018 10:28:58 +0000
> Cc: 纪秀峰 <jixiuf@qq.com>, emacs-devel@gnu.org
> 
>  I agree that customization isn't the best solution here. However, I'm suprised that `save-some-buffers'
>  still prompts even if :noprompt is passed.
>  The issue might be in `save-some-buffers': Its docstring says "If PRED is t, then certain non-file buffers
>  will also be considered.", but later it only checks whether PRED is non-nil:
> 
>                      (or
>                       (buffer-file-name buffer)
>                       (with-current-buffer buffer
>                         (or (eq buffer-offer-save 'always)
>                             (and pred buffer-offer-save (> (buffer-size) 0)))))
> 
>  Maybe instead of `pred' here we should say (eq pred t). Alternative, the predicate lambda should check
>  whether `buffer-file-name' is non-nil.
> 
> Probably the second option is better because the first option would prevent PRED from running for
> non-file-visiting buffers. Patch attached.

AFAIU, this will unconditionally disable auto-saving in *ediff-merge*
and all the similar buffers, when auto-save-visited-mode is turned
on.  Is that what we want?  And if that's going to be the default, how
are users supposed to override it if they want?