itree: Reproduce markers's behavior more faithfully (bug#58928)

The most obvious problem was the lack of support for
`insert-before-markers`, but the behavior was also different in a few
other cases.

* src/itree.h (itree_insert_gap):
* src/itree.c (itree_insert_gap): Add `before_markers` arg.
* src/lisp.h (adjust_overlays_for_insert):
* src/buffer.c (adjust_overlays_for_insert): Add `before_markers` arg.

* src/insdel.c (adjust_markers_for_replace, adjust_markers_for_insert)
(adjust_markers_for_delete): Adjust overlays directly from here.
(insert_1_both, insert_from_string_1, insert_from_gap)
(insert_from_buffer_1, adjust_after_replace, replace_range)
(replace_range_2, del_range_2): Don't adjust overlays explicitly here
any more.

* test/src/buffer-tests.el (test-overlay-insert-before-markers-empty)
(test-overlay-insert-before-markers-non-empty): New tests.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 3b0e6f1f9a1..ee0b7e13508 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -3454,20 +3454,20 @@ overlay_strings (ptrdiff_t pos, struct window *w, unsigned char **pstr)
 
 
 void
-adjust_overlays_for_insert (ptrdiff_t pos, ptrdiff_t length)
+adjust_overlays_for_insert (ptrdiff_t pos, ptrdiff_t length, bool before_markers)
 {
   if (!current_buffer->indirections)
-    itree_insert_gap (current_buffer->overlays, pos, length);
+    itree_insert_gap (current_buffer->overlays, pos, length, before_markers);
   else
     {
       struct buffer *base = current_buffer->base_buffer
                             ? current_buffer->base_buffer
                             : current_buffer;
       Lisp_Object tail, other;
-      itree_insert_gap (base->overlays, pos, length);
+      itree_insert_gap (base->overlays, pos, length, before_markers);
       FOR_EACH_LIVE_BUFFER (tail, other)
         if (XBUFFER (other)->base_buffer == base)
-          itree_insert_gap (XBUFFER (other)->overlays, pos, length);
+          itree_insert_gap (XBUFFER (other)->overlays, pos, length, before_markers);
     }
 }