Subject: bug#58518: 29.0.50; [PATCH] Turning off compilation-minor-mode removes fontification of other modes

From: Lars Ingebrigtsen <[email-masked]>
Date: Sun, 16 Oct 2022 10:24:51 +0200

Stefan Monnier <[email-masked]> writes:

> I can't remember anyone measuring the performance impact, but it does
> come at a cost since every time we call `lookup_char_property` it takes
> significantly more work.
>
> This is called at every text-property (or overlay) boundary in things
> like `next-single-property-change` and similar operations used by the
> redisplay.
>
> The "more work" is the `assq` itself whose time is proportional to the
> length of this alist, plus a `plist-get` per alias listed, whenever
> the `assq` finds a match (i.e. whenever we're looking for a property
> which has aliases).

But this would be for the *compilation* buffer only, so perhaps that's
fine...

> FWIW, in the past I suggested maybe we should introduce a notion of
> "property planes".  So `compilation` could use one property plane,
> `font-lock` could use another and they could just blindly remove all the
> properties in their plane without affecting others.

Yes, it's implementing planes, only manually.  Having real planes would
be great.

> BTW, another option is to use overlays rather than
> text-properties :-)

I'd rather not -- things are confusing enough in this area already.