src/buffer.c: Fix interaction between overlays & indirect buffers (bug#58928)

* src/buffer.c (adjust_overlays_for_insert)
(adjust_overlays_for_delete): Repeat for all buffers sharing the same text.

* src/itree.c (itree_insert_gap, itree_delete_gap): Allow an empty tree.

* test/src/buffer-tests.el (buffer-tests--overlays-indirect-bug58928):
New test.

2 files changed, 28 insertions, 10 deletions

diff --git a/src/buffer.c b/src/buffer.c
index b67b989326e..3129aa2890e 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -3456,19 +3456,37 @@ overlay_strings (ptrdiff_t pos, struct window *w, unsigned char **pstr)
 void
 adjust_overlays_for_insert (ptrdiff_t pos, ptrdiff_t length)
 {
-  /* After an insertion, the lists are still sorted properly,
-     but we may need to update the value of the overlay center.  */
-  if (! current_buffer->overlays)
-    return;
-  itree_insert_gap (current_buffer->overlays, pos, length);
+  if (!current_buffer->indirections)
+    itree_insert_gap (current_buffer->overlays, pos, length);
+  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);
+      FOR_EACH_LIVE_BUFFER (tail, other)
+        if (XBUFFER (other)->base_buffer == base)
+          itree_insert_gap (XBUFFER (other)->overlays, pos, length);
+    }
 }
 
 void
 adjust_overlays_for_delete (ptrdiff_t pos, ptrdiff_t length)
 {
-  if (! current_buffer->overlays)
-    return;
-  itree_delete_gap (current_buffer->overlays, pos, length);
+  if (!current_buffer->indirections)
+    itree_delete_gap (current_buffer->overlays, pos, length);
+  else
+    {
+      struct buffer *base = current_buffer->base_buffer
+                            ? current_buffer->base_buffer
+                            : current_buffer;
+      Lisp_Object tail, other;
+      itree_delete_gap (base->overlays, pos, length);
+      FOR_EACH_LIVE_BUFFER (tail, other)
+        if (XBUFFER (other)->base_buffer == base)
+          itree_delete_gap (XBUFFER (other)->overlays, pos, length);
+    }
 }
 
 
diff --git a/src/itree.c b/src/itree.c
index 3b10802ff09..bd4e8cc5740 100644
--- a/src/itree.c
+++ b/src/itree.c
@@ -1196,7 +1196,7 @@ void
 itree_insert_gap (struct itree_tree *tree,
                   ptrdiff_t pos, ptrdiff_t length)
 {
-  if (length <= 0 || tree->root == NULL)
+  if (!tree || length <= 0 || tree->root == NULL)
     return;
   uintmax_t ootick = tree->otick;
 
@@ -1280,7 +1280,7 @@ void
 itree_delete_gap (struct itree_tree *tree,
                   ptrdiff_t pos, ptrdiff_t length)
 {
-  if (length <= 0 || tree->root == NULL)
+  if (!tree || length <= 0 || tree->root == NULL)
     return;
 
   /* FIXME: Don't allocate stack anew every time. */