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

[Dmitry Gutov <dgutov@yandex.ru>]

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);