Avoid assertion violations in calculating line-number width

* src/indent.c (line_number_display_width): Don't use the
window's start marker if it belongs to a different buffer.
(Bug#35429)

1 files changed, 5 insertions, 2 deletions

diff --git a/src/indent.c b/src/indent.c
index 1d5d346e63f..c76e6b7b4bd 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -1968,8 +1968,11 @@ line_number_display_width (struct window *w, int *width, int *pixel_width)
          outside the accessible region, in which case we widen the
          buffer temporarily.  It could even be beyond the buffer's end
          (Org mode's display of source code snippets is known to cause
-         that), in which case we just punt and start from point instead.  */
-      if (startpos.charpos > Z)
+         that) or belong to the wrong buffer, in which cases we just
+         punt and start from point instead.  */
+      if (startpos.charpos > Z
+          || !(BUFFERP (w->contents)
+               && XBUFFER (w->contents) == XMARKER (w->start)->buffer))
         SET_TEXT_POS (startpos, PT, PT_BYTE);
       if (startpos.charpos < BEGV || startpos.charpos > ZV)
         {