emacs-29 0a5615669a4: Don't completely clip into visible range in treesit_record_change

[Yuan Fu]

branch: emacs-29
commit 0a5615669a4f5d7e2db3c4117f3c2440e9c4cfd5
Author: Yuan Fu <casouri@gmail.com>
Commit: Yuan Fu <casouri@gmail.com>

    Don't completely clip into visible range in treesit_record_change
    
    (Bug#61369)
    
    From
        min (visible_end, max (visible_beg, new_end_byte)) - visible_beg
    to
        max (visible_beg, new_end_byte) - visible_beg
    
    * src/treesit.c (treesit_record_change): We don't clip the new end
    into the visible range anymore.  If you think of it, when inserting in
    a narrowed region, the visible region is always extended to
    accommodate more text, rather than pushing text at the end to keep the
    size of the visible region.
---
 src/treesit.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/treesit.c b/src/treesit.c
index cab2f0d5354..08119f149b7 100644
--- a/src/treesit.c
+++ b/src/treesit.c
@@ -770,7 +770,8 @@ treesit_record_change (ptrdiff_t start_byte, ptrdiff_t 
old_end_byte,
       treesit_check_parser (lisp_parser);
       TSTree *tree = XTS_PARSER (lisp_parser)->tree;
       /* See comment (ref:visible-beg-null) if you wonder why we don't
-      update visible_beg/end when tree is NULL.  */
+        update visible_beg/end when tree is NULL.  */
+
       if (tree != NULL)
        {
          eassert (start_byte <= old_end_byte);
@@ -794,8 +795,14 @@ 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))
+         /* We don't clip new_end_offset under visible_end, because
+             inserting in narrowed region always extends the visible
+             region.  If we clip new_end_offset here, and re-add the
+             clipped "tail" in treesit_sync_visible_region later,
+             while it is technically equivalent, tree-sitter's
+             incremental parsing algorithm doesn't seem to like it
+             (bug#61369).  */
+         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);
@@ -817,11 +824,13 @@ treesit_record_change (ptrdiff_t start_byte, ptrdiff_t 
old_end_byte,
            /* Move forward.  */
            visi_beg_delta = (old_end_byte < visible_beg
                              ? new_end_byte - old_end_byte : 0);
+
          XTS_PARSER (lisp_parser)->visible_beg = visible_beg + visi_beg_delta;
          XTS_PARSER (lisp_parser)->visible_end = (visible_end
                                                   + visi_beg_delta
                                                   + (new_end_offset
                                                      - old_end_offset));
+
          eassert (XTS_PARSER (lisp_parser)->visible_beg >= 0);
          eassert (XTS_PARSER (lisp_parser)->visible_beg
                   <= XTS_PARSER (lisp_parser)->visible_end);