bug#52018: 28.0.60; Improve documentation for compilation-finish-functions

[Eli Zaretskii]

> From: Thibault Polge <thibault@thb.lt>
> Cc: 52018@debbugs.gnu.org
> Date: Mon, 22 Nov 2021 10:12:46 +0100
> 
> > OK, then the info is also on the mode line and can be taken from
> > there.
> 
> I'm not sure I follow you. Are you suggesting functions in
> `compilation-finish-functions` should scrape the mode line to get the
> compilation process' exit status, instead of just using the string
> argument they receive?

No need to scrape the mode line: the info is readily available in
mode-line-process.

If the purpose is to provide the exit status to the function, we need
to take care to pass it without any massaging.  We don't make a point
of doing that now, so I'd prefer not to document this in such certain
terms, as people will then complain that it isn't 100% accurate.