bug#65451: 30.0.50; `after-change-functions' are not triggered in the same order the changes are made

[Ihor Radchenko <yantar92@posteo.net>]

Eli Zaretskii <eliz@gnu.org> writes:

>> Then, I'd like to point back to the previous discussion where I asked to
>> expose to Elisp information about buffer changes available to
>> tree-sitter.
>> https://yhetil.org/emacs-devel/83tu8jq2vl.fsf@gnu.org/
>
> I don't want to do that, sorry.  Not without a good understanding of
> what exactly do you need from that and in what way.  If we will expose
> anything, it will have to be the minimum possible exposure, not the
> maximum, so I would like to understand this very well before I agree
> to any change in this direction.

Org wants to do the same thing tree-sitter does - keep parsed AST in
sync with buffer modifications without having to re-parse the whole
buffer. So, we basically need the same information tree-sitter needs -
the sequence of buffer text changes, in their order.

Note that the markers discussed in the thread I linked are not
sufficient. When editing near AST node boundaries, even if the
boundaries are represented by markers, we have to re-parse the AST
around to account for the possible structural changes. So, information
about buffer edits is still required.

>> In fact, I am not sure if tree-sitter will behave correctly if it is
>> signaled changes in incorrect order.
>
> I will defer to Yuan, but tree-sitter doesn't use these hooks, we call
> its functions directly from insdel.c where needed.  This makes sense
> for a library to which we link and whose interface code we control,
> but giving such access to Lisp (and Org on top of that) is out of the
> question.  We don't even give such access to modules.

I hope that we can solve this issue one way or another. This currently
breaks the very core functionality of Org. Every part of Org relies on
it to obtain reasonable performance. Prior to using cache, we had orders
of magnitude slowdowns.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
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