bug#64230: 30.0.50; Ibuffer reports 1 file too many with ibuffer-auto-mode enabled

[Stephen Berman <stephen.berman@gmx.net>]

On Sun, 10 Sep 2023 07:11:07 -0700 Stefan Kangas <stefankangas@gmail.com> wrote:

> Stephen Berman <stephen.berman@gmx.net> writes:
>
>> 0. emacs -Q
>> 1. Type `M-x' and then TAB to pop up the *Completions* buffer, then type
>>    `C-g'.
>> 2. Type `M-x ibuffer'.
>> 3. Type `d' on the lines for the buffers *scratch* and *Completions* to
>>    flag them for deletion.
>> 4. Type `C-c C-a' to enable ibuffer-auto-mode.
>> 5. Type `x' and at the prompt "Really kill 2 buffers? (y or n)" type `y'.
>> => The *Ibuffer* lines for  *scratch* and *Completions* are deleted and
>>    the echo area displays this message: "Operation finished; killed 3
>>    buffers".
>>
>> If you change this recipe by omitting step 4, then after the buffer
>> lines are deleted the message displayed is "Operation finished; killed 2
>> buffers".
>>
>> The unexpected message with ibuffer-auto-mode enabled is displayed in
>> Emacs 27-30 but not in Emacs 26.  With Emacs 27+, on typing `x' at step
>> 5, the buffer *Ibuffer confirmation* pops up and a line for this buffer
>> immediately appears in the *Ibuffer* display, and this is counted by the
>> function `ibuffer-map-lines', and on typing `y' not only are the two
>> flagged buffers deleted, but also *Ibuffer confirmation*, hence "killed
>> 3 buffers".  In contrast, in Emacs 26, the popped up buffer *Ibuffer
>> confirmation* does not get added to the *Ibuffer* display and thus is
>> not counted by `ibuffer-map-lines'.
>>
>> AFAICT, this difference is not due to any ibuffer code changes after
>> Emacs 26; rather, there appears to be a timing difference with respect
>> to when Emacs updates the *Ibuffer* display: when I instrument
>> `ibuffer-update' for Edebug and then type `x' (step 5 above), what
>> happens in Emacs 26 is that I can confirm with `y', then the flagged
>> lines are deleted, and only then does Edebug stop the execution so I can
>> step into `ibuffer-update'; while in Emacs 27+, as soon as I type `x',
>> Edebug stops execution, i.e., before the flagged lines are deleted.
>>
>> `ibuffer-update' is called in `ibuffer-auto-update-changed', which is
>> added to post-command-hook in `ibuffer-auto-mode'.  So it seems that in
>> Emacs 26 post-command-hook runs or takes effect later than in Emacs 27+.
>> Whether this is really the case, and if so, what change it is due to, I
>> haven't determined, and I don't know how restore the Emacs 26 execution
>> order (or if that's even desirable).  But even if the difference is due
>> to something else, the message displayed in Emacs 27+ after the deletion
>> of the *Ibuffer* lines is at least misleading, since it clearly is meant
>> to refer only to the flagged lines, as in Emacs 26.
>>
>> In lieu of a real fix, since it is, AFAICS, only the transient buffer
>> *Ibuffer confirmation* that results in the problematic message, a
>> workaround is simply to decrement the line count by one when
>> ibuffer-auto-mode is enabled, as in the the attached patch (which also
>> takes the opportunity to wrap an overlong line in `ibuffer-map-lines').
>
> Your analysis and patch makes sense to me.  Please install, but add a
> brief comment explaining why we do that decrement there.

Done, and pushed as commit ca95e45f7e8.  Thanks.

Steve Berman