Subject: Re: bug#34525: replace-regexp missing some matches

From: Alan Mackenzie <[email-masked]>
Date: Wed, 27 Feb 2019 14:22:51 +0000

Hello, Stefan.

On Tue, Feb 26, 2019 at 15:09:54 -0500, Stefan Monnier wrote:
> > 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.

> Hmm... gl_state is not supposed to be kept "live" across buffer
> modifications.  It's supposed to be used only *within* read-only
> primitives which set it from scratch at the beginning (by calling
> SETUP_SYNTAX_TABLE, SETUP_BUFFER_SYNTAX_TABLE, or
> SETUP_SYNTAX_TABLE_FOR_OBJECT).  The backward_i and forward_i fields are
> actually reset in the first call to update_syntax_table, by passing it
> a true value for the `init` arg.

> So the problem you describe might be due to some place where we fail to
> reset gl_state before using it, or maybe it's a bug in
> SETUP_*_SYNTAX_TABLE*

I see another potential problem, and I'd like your view on it, please.

Namely, in next_interval, we have

  if (! NULL_RIGHT_CHILD (i))
    {
      i = i->right;
      while (! NULL_LEFT_CHILD (i))
        i = i->left;                  <===============

      i->position = next_position;
      return i;
    }

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.  Thus if we use this
interval as an argument to update_interval, we will likely fail.  I
think this can happen in update_syntax_table.

There is an analogous situation in previous_interval.

I might try adding code to this to set these ->position's.  Trouble is,
it might slow things down quite a bit.

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).