bug#49700: 27.2; [PATCH] Refactor minibuffer aborting

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

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: <miha@kamnitnik.top>
>> Cc: acm@muc.de, 49700@debbugs.gnu.org
>> Date: Fri, 23 Jul 2021 09:26:21 +0200
>> 
>> > Thanks, but could you please explain the rationale and the motivation
>> > for these changes?
>> 
>> Refactoring to have cleaner code.
>> 
>> Right now, without applying this patch, quitting multiple recursive
>> edits (in minibuffer-exit) is achieved by extra special handling in
>> internal_catch.  In my opinion, it's cleaner to avoid adding such code
>> into a core function like internal_catch if possible.  This patch moves
>> this code into the function minibuffer-exit, and by using closures, it
>> achieves the same effect without a global variable
>> (minibuffer_quit_level).
>> 
>> In other words, without this patch, Fminibuffer_exit cooperates with
>> internal_catch through a global variable.  And with this patch,
>> Fminibuffer_exit cooperates with command_loop by passing it a closure.
>> 
>> Fminibuffer_exit was moved to lisp because its easier to make closures
>> in lisp.
>> 
>> minibuffer-alist was introduced because it's needed by minibuffer-exit.
>> I also think that it's nice to expose the list of minibuffers to lisp.
>
> Thanks.
>
> I'd prefer not to expose minibuffer-alist to Lisp if it can be
> avoided.  This is a tricky area of Emacs, and exposing it to Lisp IMO
> gives Lisp programmers too much rope to hang themselves.

Well, the minibuffer list is already kind of exposed to lisp, try:
(seq-filter #'minibufferp (buffer-list))

minibuffer-alist returns a newly constructed list, similar to
buffer-list, so modifying the list structure is safe.  What could be
unsafe is modifying the minibuffers themselves, renaming or killing
them.  I believe that, since such actions are possible without the use
of minibuffer-alist
(for example, by evaluating (kill-buffer " *Minibuf-1")), they should
not mess up Emacs internals and it should be treated as a bug if they
do.

> Is it feasible to make these changes without exposing the alist?

Yes it is feasible.  If the above didn't convince you, please send
another e-mail and I will try.  Thanks.

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