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, 22 insertions, 0 deletions

diff --git a/test/src/buffer-tests.el b/test/src/buffer-tests.el
index b96a8dcacd2..a39d7d51de1 100644
--- a/test/src/buffer-tests.el
+++ b/test/src/buffer-tests.el
@@ -528,6 +528,28 @@ with parameters from the *Messages* buffer modification."
 (deftest-overlay-start/end-1 L (1 0) (1 1))
 (deftest-overlay-start/end-1 M (0 0) (1 1))
 
+(ert-deftest test-overlay-insert-before-markers-empty ()
+  (with-temp-buffer
+    (insert "1234")
+    (goto-char (1+ (point-min)))
+    (let ((overlay (make-overlay (point) (point))))
+      (insert-before-markers "x")
+      (should (equal (point) (overlay-end overlay)))
+      (should (equal (point) (overlay-start overlay))))))
+
+(ert-deftest test-overlay-insert-before-markers-non-empty ()
+  (with-temp-buffer
+    (insert "1234")
+    (goto-char (+ 2 (point)))
+    (let ((overlay (make-overlay (1- (point)) (point))))
+      (insert-before-markers "x")
+      (should (equal (point) (overlay-end overlay)))
+      (should (equal (- (point) 2) (overlay-start overlay)))
+      (forward-char -2)
+      (insert-before-markers "y")
+      (should (equal (+ 2 (point)) (overlay-end overlay)))
+      (should (equal (point) (overlay-start overlay))))))
+
 (ert-deftest test-overlay-start/end-2 ()
   (should-not (overlay-start (with-temp-buffer (make-overlay 1 1))))
   (should-not (overlay-end (with-temp-buffer (make-overlay 1 1)))))