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.

1 files 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);