Subject: Re: bug#64394: [PATCH] Fix `async-shell-command-display-buffer' display

From: Eliza Velasquez <[email-masked]>
Date: Sat, 01 Jul 2023 00:52:32 -0700

On Sat, Jul 01 2023 at 10:24 +03, Eli Zaretskii <[email-masked]> wrote:

> I'm probably missing something, but how can display-buffer fail to
> support any action function, such as display-buffer-no-window?
>
> Martin, what am I missing here?

I was also confused.  Based on the documentation for
`display-buffer-no-window', it seems that callers are supposed to
explicitly pass an `(allow-no-window . t)' cons pair when calling
`display-buffer' as a signal that they can correctly handle a return
value of nil.  If it's absent, `display-buffer-no-window' seems to err
on the side of caution, assume the caller can't handle nil, displays the
window anyway, and returns it like all the other display functions.

Technically it seems that you can add `(allow-no-window . t)' to
`display-buffer-alist' to always force the buffer never to appear, but
that doesn't seem at all like its intended use.

> That's fine, but those are your preferences.  I'd feel uncomfortable
> with forcing them on everyone, if we already have a way of tailoring
> this behavior by user customizations.

I might not have been clear with what I meant here, sorry; I mean that
in my own personal config, when I run `mpv', its output appears in a
buffer named `*shell:mpv*' instead of `*Async Shell Command*', and I
have an explicit entry for it in `display-buffer-alist' so that it
doesn't appear via `display-buffer-no-window'.  This was functioning
well, except the moment I set `async-shell-command-display-buffer' to
nil, the buffer displayed itself the moment mpv began to write to
stdout.

A minimally reproable example in `emacs -Q':

--8<---------------cut here---------------start------------->8---
(setq display-buffer-alist
      '(("\\*Async Shell Command\\*"
	 (display-buffer-no-window))))
(setq async-shell-command-display-buffer nil)
--8<---------------cut here---------------end--------------->8---

`M-& echo foo RET' will unexpectedly show the `*Async Shell Command*'
buffer.

-- 
Eliza