bug#34525: replace-regexp missing some matches

[Stefan Monnier]

>> Here, in seeking the next interval, we go down a chain of `left's.  We
>> do not set the ->position field of these intervals, except for the last
>> one, which we return.
>> So the returned interval doesn't satisfy the condition that all its
>> parents have their ->position's set correctly.
[...]
> I've done this, and it appears to have fixed the bug.  :-)

AFAICT the only place where we need the parents to have
a valid ->position is in update_interval.  So maybe another fix is to
change update_interval so it computes the parent's ->position rather
than rely on it having the right value.

I personally don't have a preference and I'm not sure which option would
be better performancewise.

If we opt (like your patch does) to have the invariant that
the ->position of parents is kept up-to-date, then maybe we should
change find_interval to guarantee this (which would basically be
a matter of moving the corresponding code from update_syntax_table where
we update the parents's ->position after calling find_interval) ?


        Stefan