bug#33740: [PATCH] Customizable flymake mode-line indicator

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 33740@debbugs.gnu.org,  joaotavora@gmail.com,  andreyk.mad@gmail.com
> Date: Thu, 19 Sep 2019 18:23:01 +0200
> 
> Lars Ingebrigtsen <larsi@gnus.org> writes:
> 
> > But the code in that function could be clearer -- I don't really
> > understand why this is done at all.
> 
>               aelt = Fassoc (elt, mode_line_proptrans_alist, Qnil);
>               if (! NILP (aelt) && !NILP (Fequal (props, XCDR (aelt))))
>                 {
>                   /* AELT is what we want.  Move it to the front
>                      without consing.  */
>                   elt = XCAR (aelt);
>                   mode_line_proptrans_alist
>                     = move_elt_to_front (aelt, mode_line_proptrans_alist);
>                 }
>               else
>                 {
>                   Lisp_Object tem;
> 
>                   /* If AELT has the wrong props, it is useless.
>                      so get rid of it.  */
> 
> 
> Oh, this entire thing is just so that we can maintain a cache of text
> properties and avoid some consing?  And if we have a cache, then all the
> characters in the element has to have the same text properties.

Yes.

> I wonder whether all this is really warranted...

It is.  Redrawing the mode line is a very frequent redisplay thing, so
optimizing the heck out of it is justified.

That's what I meant when I said "wisely": you need to create faces in
advance, and take care to have each individual string you use to be of
a uniform face.  And don't use propertize.