Re: no buffer to flush the error output in ?

[Eli Zaretskii]

> Date: Wed, 18 Sep 2024 01:04:25 +0200
> Cc: emacs-devel@gnu.org
> From: Phil Estival <pe@7d.nz>
> 
> I had missed [[info:elisp#Asynchronous Processes][elisp#Asynchronous 
> Processes]].  make-process can have a buffer or a pipe process attached
> to the standard error of subprocess.  (If STDERR is nil, standard error 
> is mixed with standard output).

We do have a solution for async subprocesses, but you specifically
asked about synchronous subprocesses, and the passage from the manual
which you quoted was talking about synchronous subprocesses, and only
about them.

> My questionning comes from an interactive command shell based on comint,
> the performance are not significant. In the end the output has to be
> separated somehow (prompt, result output and errors). When not
> separating the channels, additional escapde codes are needed
> plus various semantics that has to be filtered with regex acrobatics,
> e.g.
> - 165 matches in 147 lines for "regex" in buffer: comint.el.gz<28.2>

If you use comint, then you are using async subprocesses, don't you?
If so using :stderr attribute (and/or pipe processes) is what you
want, I think.