bug#61369: Problem with keeping tree-sitter parse tree up-to-date

[Yuan Fu]

> On Feb 15, 2023, at 2:44 PM, Dmitry Gutov <dgutov@yandex.ru> wrote:
> 
> On 15/02/2023 04:17, Dmitry Gutov wrote:
>> Seems like treesit_record_change turns new_end_byte=69 into new_end_byte=67 
>> inside treesit_tree_edit_1.
>> It seems to fail in this calculation:
>>   ptrdiff_t new_end_offset = (min (visible_end,
>>                    max (visible_end, new_end_byte))
>>                   - visible_beg);
>> because visible_end is still 68 there. It value gets updated later, closer 
>> to the end of this function.
> 
> So FWIW the patch below fixes the problem. But I'm not sure about change's 
> clipping by the current restriction, or how it should be handled exactly.
> 
> diff --git a/src/treesit.c b/src/treesit.c
> index cab2f0d5354..9f15b88a8bd 100644
> --- a/src/treesit.c
> +++ b/src/treesit.c
> @@ -794,9 +794,7 @@ treesit_record_change (ptrdiff_t start_byte, ptrdiff_t 
> old_end_byte,
>  ptrdiff_t old_end_offset = (min (visible_end,
>   max (visible_beg, old_end_byte))
>      - visible_beg);
> -  ptrdiff_t new_end_offset = (min (visible_end,
> -   max (visible_beg, new_end_byte))
> -      - visible_beg);
> +  ptrdiff_t new_end_offset = max (visible_beg, new_end_byte) - visible_beg;
>  eassert (start_offset <= old_end_offset);
>  eassert (start_offset <= new_end_offset);

Thank you very much! I thought that clipping the change into the fixed visible 
range, and rely on treesit_sync_visible_region to add back the clipped “tail” 
when we extend the visible range would be equivalent to not clipping, but I 
guess clipping and re-adding affects how incremental parsing works inside 
tree-sitter.

I don’t think this change would have any adverse effect, because if you think 
of it, inserting text in a narrowed region always extends the region, rather 
than pushing text at the end out of the narrowed region. So the right thing to 
do here is in fact not clipping new_end_offset.

I pushed this change.

Yuan