bug#72426: 29.2.50; comint-pager doesn't affect async-shell-command

[Eli Zaretskii <eliz@gnu.org>]

> From: Spencer Baugh <sbaugh@janestreet.com>
> Cc: Jim Porter <jporterbugs@gmail.com>,  72426@debbugs.gnu.org
> Date: Wed, 07 Aug 2024 11:05:47 -0400
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> >> Date: Tue, 6 Aug 2024 19:36:15 -0700
> >> Cc: 72426@debbugs.gnu.org
> >> From: Jim Porter <jporterbugs@gmail.com>
> >> 
> >> Just to be extra-sure, I tried using 'async-shell-command' to run "git 
> >> log" with PAGER unset, and sure enough it tried to use "less" for 
> >> paging, which didn't go very well. "PAGER=cat" was much better.
> >
> > Did you try with process-connection-type nil?
> 
> With process-connection-type nil, git will never run a pager (since like
> many programs it checks whether stdout is a terminal before doing so).
> 
> So both:
> 
> (let ((process-connection-type nil)
>       (process-environment (cons '("PAGER" "less") process-environment)))
>   (async-shell-command "git log"))
> 
> and
> 
> (let ((process-connection-type nil)
>       (process-environment (cons "PAGER" process-environment)))
>   (async-shell-command "git log"))
> 
> behave identically.
> 
> Setting PAGER=cat is only necessary for process-connection-type=t.

As expected.  The problem is that a Lisp program could let-bind this
variable around a call to async-shell-command (or some other similar
API), in which case a setting in startup.el will not catch that.  But
maybe we don't care, since a program whose stdout is not a console
device will ignore PAGER anyway.