Re: What's the best (i.e. least bad) way to re-redisplay?

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan.

On Thu, Aug 26, 2021 at 09:49:33 -0400, Stefan Monnier wrote:
> >> > I think something along the lines of

> >> >     (run-with-timer 0 nil
> >> >                     (lambda (buf)
> >> >                       (with-current-buffer buf (font-lock-flush)))
> >> >                     (current-buffer))

> >> > is the cleanest that comes to mind.

> >> Thanks.  That's probably cleaner than a direct use of
> >> jit-lock-force-redisplay.

> > Why is it cleaner?  jit-lock and font-lock include provision for the
> > fontification function to tell jit-lock what was the region actually
> > fontified, and that will trigger a call to jit-lock-force-redisplay in
> > a timer.  Why not use an existing mechanism?

> That's indeed another option.  I assumed that the situation is such that
> while fontifying region POS1..POS2 we discover a new type that forces
> the whole buffer to be refontified (or at least some region POS3..POS4),
> in which case it's best to use `font-lock-flush` and let this
> refontification happen lazily.

My idea is that, say, a new type "foo" is found by stealth fontification.
CC Mode will then do a regexp search for "\\_<foo\\_>" from BOB to EOB
removing 'fontified text properties from each match it finds.  This is
fast (around 10ms per found type in xdisp.c).  It should be enough to
force (re)fontification of (the statements containing) "foo" whenever
these occurrences are scrolled onto.  Then there's the currently
displayed window, as we've been discussing.

That, of course, involves somehow persuading the user to enable stealth
fontification.

> But if indeed we can cheaply adjust the few places in the buffer that
> are affected without performing a full "refontify" it might indeed be
> a good idea to do that and adjust the `jit-lock-bounds` return value,
> but in that case we have to be sure that the new bounds indeed describe
> an area of the buffer that is now fully fontified, which is likely to be
> a problem because there is no reason to assume that the buffer outside
> of POS1..POS2 had already been fontified, so it may force us to eagerly
> fontify additional parts of POS3..POS4.

> Another option if we can cheaply adjust the few places in the buffer that
> are affected without performing a full "refontify", is to do those
> adjustments and then only force a redisplay but not a refontification.

This is exactly my plan.

> I think this can be done with something like:

>     (run-with-timer 0 nil
>                     (lambda (buf)
>                       (with-current-buffer buf
>                         (put-text-property (point-min) (point-max) 'cc-dummy t)
>                         (remove-text-properties (point-min) (point-max) '(cc-dummy))))
>                     (current-buffer))

I don't understand what that bit of code's doing.

> -- Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).