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

[Spencer Baugh <sbaugh@janestreet.com>]

Eli Zaretskii <eliz@gnu.org> writes:
>> 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.

Yes, I'm just not sure the right approach.  It would be wasteful to
return the comparison function from the annotation function every time
it's called, since it's the same for every call.

>> >> 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.

Would it be OK for compile.el to start storing this data in a variable?
The number of errors/warnings/infos is already stored; also storing the
exit status would probably be useful for all kinds of things.