bug#63411: [PATCH] pcomplete/systemctl cannot complete units for old versions of systemd

[Eli Zaretskii <eliz@gnu.org>]

> From: Liu Hui <liuhui1610@gmail.com>
> Date: Wed, 17 May 2023 16:53:13 +0800
> 
> Here is the patch that fixes the problem.
> 
> From aaba4753ada1c003171d9a5342c87a945992e62f Mon Sep 17 00:00:00 2001
> From: Liu Hui <liuhui1610@gmail.com>
> Date: Wed, 17 May 2023 16:39:18 +0800
> Subject: [PATCH] Fix systemd unit completion for old versions of systemd
> 
> * lisp/pcmpl-linux.el (pcmpl-linux--systemd-units): Use '--no-legend'
> for compatibility.
> ---
>  lisp/pcmpl-linux.el | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lisp/pcmpl-linux.el b/lisp/pcmpl-linux.el
> index 082072d87d2..589b4799c8d 100644
> --- a/lisp/pcmpl-linux.el
> +++ b/lisp/pcmpl-linux.el
> @@ -119,7 +119,8 @@ pcmpl-linux--systemd-units
>    (with-temp-buffer
>      (apply #'call-process
>             "systemctl" nil '(t nil) nil
> -           "list-units" "--full" "--legend=no" "--plain" args)
> +           ;; "--legend=no" doesn't exist before systemd v248
> +           "list-units" "--full" "--no-legend" "--plain" args)
>      (goto-char (point-min))
>      (let (result)
>        (while (re-search-forward (rx bol (group (+ (not space)))
> -- 
> 2.25.1

Thanks.

I'm not an expert on systemctl; would someone who uses that please
tell if this could have any downsides?  E.g., is --no-legend expected
to be deprecated, perhaps resulting in a warning message or something?
If not, why did the systemd developers add another option with the
same semantics?