bug#44824: [PATCH] org.el: Avoid xdg-open silent failure

[Eli Zaretskii <eliz@gnu.org>]

> From: Maxim Nikulin <m.a.nikulin@gmail.com>
> Date: Fri, 19 Feb 2021 19:29:49 +0700
> Cc: 44824@debbugs.gnu.org
> 
> > On Windows Emacs always uses pipes, because we don't have PTYs there.
> > And there's no xdg-open on MS-Windows anyway, so it's a moot point.
> 
> Should I consider your response as a suggestion to remove the `if' 
> related to `system-type'?

Yes, that 'if' isn't necessary.

> If I remember correctly, on windows it is possible to communicate with a 
> process through stdin and stdout only if the application is compiled as 
> a *console* one.

That's true.  But in this case we don't really want to communicate
with the sub-process, do we?  We just want to invoke it and let it
run.  So the fact that there's no way of communicating with the
sub-process is not important here, as the pipes will not be used.  We
just need to specify pipes because that works around the problem with
xdg-open.

> "start file.pdf" executed in cmd.exe launches an application that does 
> not block command prompt. In this sense it similar to background 
> processes launched by kde-open5 or "gio open". However I am unaware if 
> there is something similar to process groups on windows that leads to 
> termination of all group members when leader process finishes.

Things are fairly similar on Windows.  But is this really relevant to
the issue at hand?  There's no xdg-open on Windows, so whatever
problems you had with xdg-open will never happen on Windows.  the
proposed patch fixes the problem only on systems where org.el invokes
the PDF viewer via xdg-open.  Right?