bug#34525: replace-regexp missing some matches

[Eli Zaretskii]

> Date: Tue, 26 Feb 2019 13:50:48 +0000
> Cc: daniel.lopez999@gmail.com, 34525@debbugs.gnu.org, monnier@iro.umontreal.ca
> From: Alan Mackenzie <acm@muc.de>
> 
> > So you are saying that gl_state uses a stale offset, which should have
> > been updated due to the previous replacements?
> 
> More precisely, I think that the interval containing "Bitmap<" has not
> been adjusted after the replacement of "Bitmap.h" by "SharedBitmap.h"
> early in the .h file.

In general, I don't believe this can happen, because otherwise we
would see the faces in the wrong places.  The interval tree does get
updated after each buffer change.

However, if some interval data is cached, as you seem to imply:

> gl_state contains a cached interval, gl_state->backward_i, and there is
> no guarantee that its ->position will have been updated by
> adjust_intervals_for_insertion.  In the current bug, I believe it hasn't
> been adjusted.

then yes, that cached interval data might not be updated.  But I
wonder why you say "there is no guarantee" -- don't you actually see
stale data there in this scenario?

> The function update_syntax_table uses gl_state->backward_i to manoevre
> its way to the current interval using update_interval.  If
> gl_state->backward_i->position hasn't already been adjusted for the
> insertion, the interval update_interval returns won't have been adjusted
> either.
> 
> I'm reasonably sure this is what's happening:
> adjust_intervals_for_insertion is failing to adjust the cached intervals
> in gl_state.  It's a nasty cache invalidation problem.

Do we really have to guess here?  Isn't there anyone who knows how
this works?  Stefan?