bug#63896: [PATCH] Support annotating and sorting the project list during completion

[Eli Zaretskii <eliz@gnu.org>]

> From: Spencer Baugh <sbaugh@janestreet.com>
> Cc: 63896@debbugs.gnu.org
> Date: Thu, 15 Jun 2023 15:04:20 -0400
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> I'd be happy to use a cons or a vector, or even a more complicated
> >> structure, but I didn't see an easy way to do comparison of
> >> complicated structures, for the sorting of projects based on their
> >> annotation.  For example, if I have values of the form
> >> (num . (num num num))
> >
> > You'd need to write a custom comparison function, but why is that a
> > problem?
> 
> Yes, but how does that get configured?
> 
> >> there's no way to know what sorting predicate to use for such values - I
> >> need to be able to know which value should sort sort first, when I have
> >> a pair of them.
> >
> > But the encoding scheme above provides the answer: you want errors to
> > sort before the warnings.  So it sounds like you already decided how
> > to sort those, no?
> 
> Yes, but I mean that *this function* doesn't know, given some opaque
> value returned by a user-provided annotation function, how to sort.

You'd need to include the comparison function in the annotation data,
I guess.

> >> Would it be OK to make compile.el store the exit code as a number in a
> >> variable and then use that?  Then I wouldn't need to touch
> >> mode-line-process at all.
> >
> > I don't see why you'd need that.  Doesn't process-exit-status give you
> > that value?  mode-line-process is not some magic, it just accesses
> > process information exposed via the different primitives.
> 
> For sure, process-exit-status gives me that value.  But how do I get the
> process to call it on?  The process is dead at this point, so
> (get-buffer-process "*compilation*") returns nil.  Is there a way to get
> the process associated with the buffer even though it's killed?

If project.el wants to access data from an exited compilation, it
needs to record that when the compilation exits (via the
compilation-finish-functions hook, for example).  Calling
format-mode-line will not help you, because if the process doesn't
exist, its data cannot be accessed, and relying on what's displayed on
the mode line is a bad idea: it could be outdated or even irrelevant.
So please don't use such kludges, even though they might look
convenient at first sight.