Fix C-p and C-n when wrap-prefix is too wide

* src/xdisp.c (move_it_in_display_line_to): Avoid looping in
previous/next-line when wrap-prefix is set to a too-wide
stretch of whitespace.  (Bug#30432)

(cherry picked from commit 842b3d7412eaed6b2c9f90c3361abb4932ec0b1d)

1 files changed, 17 insertions, 1 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 2142d771e2d..d28c1140678 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -9211,9 +9211,25 @@ move_it_in_display_line_to (struct it *it,
       prev_method = it->method;
       if (it->method == GET_FROM_BUFFER)
         prev_pos = IT_CHARPOS (*it);
+
+      /* Detect overly-wide wrap-prefixes made of (space ...) display
+         properties.  When such a wrap prefix reaches past the right
+         margin of the window, we need to avoid the call to
+         set_iterator_to_next below, so that it->line_wrap is left at
+         its TRUNCATE value wisely set by handle_line_prefix.
+         Otherwise, set_iterator_to_next will pop the iterator stack,
+         restore it->line_wrap, and we might miss the opportunity to
+         exit the loop and return.  */
+      bool overwide_wrap_prefix =
+        CONSP (it->object) && EQ (XCAR (it->object), Qspace)
+        && it->sp > 0 && it->method == GET_FROM_STRETCH
+        && it->current_x >= it->last_visible_x
+        && it->continuation_lines_width > 0
+        && it->line_wrap == TRUNCATE && it->stack[0].line_wrap != TRUNCATE;
       /* The current display element has been consumed.  Advance
          to the next.  */
-      set_iterator_to_next (it, true);
+      if (!overwide_wrap_prefix)
+        set_iterator_to_next (it, true);
       if (IT_CHARPOS (*it) < CHARPOS (this_line_min_pos))
         SET_TEXT_POS (this_line_min_pos, IT_CHARPOS (*it), IT_BYTEPOS (*it));
       if (IT_CHARPOS (*it) < to_charpos)