Fix bug in displaying header line with a box face

* src/xdisp.c (get_next_display_element): Handle the case when a
display string acquires the box face from an underlying string,
not from the buffer.  (Bug#23091)

1 files changed, 47 insertions, 14 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index d68244e6c9d..d6ee2de8f39 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -7229,18 +7229,21 @@ get_next_display_element (struct it *it)
                 {
                   ptrdiff_t ignore;
                   int next_face_id;
+                  bool text_from_string = false;
+                  /* Normally, the next buffer location is stored in
+                     IT->current.pos...  */
                   struct text_pos pos = it->current.pos;
 
-                  /* For a string from a display property, the next
-                     buffer position is stored in the 'position'
+                  /* ...but for a string from a display property, the
+                     next buffer position is stored in the 'position'
                      member of the iteration stack slot below the
                      current one, see handle_single_display_spec.  By
-                     contrast, it->current.pos was not yet updated
-                     to point to that buffer position; that will
-                     happen in pop_it, after we finish displaying the
-                     current string.  Note that we already checked
-                     above that it->sp is positive, so subtracting one
-                     from it is safe.  */
+                     contrast, it->current.pos was not yet updated to
+                     point to that buffer position; that will happen
+                     in pop_it, after we finish displaying the current
+                     string.  Note that we already checked above that
+                     it->sp is positive, so subtracting one from it is
+                     safe.  */
                   if (it->from_disp_prop_p)
                     {
                       int stackp = it->sp - 1;
@@ -7249,19 +7252,49 @@ get_next_display_element (struct it *it)
                       while (stackp >= 0
                              && STRINGP ((it->stack + stackp)->string))
                         stackp--;
-                      eassert (stackp >= 0);
-                      pos = (it->stack + stackp)->position;
+                      if (stackp < 0)
+                        {
+                          /* If no stack slot was found for iterating
+                             a buffer, we are displaying text from a
+                             string, most probably the mode line or
+                             the header line, and that string has a
+                             display string on some of its
+                             characters.  */
+                          text_from_string = true;
+                          pos = it->stack[it->sp - 1].position;
+                        }
+                      else
+                        pos = (it->stack + stackp)->position;
                     }
                   else
                     INC_TEXT_POS (pos, it->multibyte_p);
 
-                  if (CHARPOS (pos) >= ZV)
+                  if (text_from_string)
+                    {
+                      Lisp_Object base_string = it->stack[it->sp - 1].string;
+
+                      if (CHARPOS (pos) >= SCHARS (base_string) - 1)
+                        it->end_of_box_run_p = true;
+                      else
+                        {
+                          next_face_id
+                            = face_at_string_position (it->w, base_string,
+                                                       CHARPOS (pos), 0,
+                                                       &ignore, face_id, false);
+                          it->end_of_box_run_p
+                            = (FACE_FROM_ID (it->f, next_face_id)->box
+                               == FACE_NO_BOX);
+                        }
+                    }
+                  else if (CHARPOS (pos) >= ZV)
                     it->end_of_box_run_p = true;
                   else
                     {
-                      next_face_id = face_at_buffer_position
-                        (it->w, CHARPOS (pos), &ignore,
-                         CHARPOS (pos) + TEXT_PROP_DISTANCE_LIMIT, false, -1);
+                      next_face_id =
+                        face_at_buffer_position (it->w, CHARPOS (pos), &ignore,
+                                                 CHARPOS (pos)
+                                                 + TEXT_PROP_DISTANCE_LIMIT,
+                                                 false, -1);
                       it->end_of_box_run_p
                         = (FACE_FROM_ID (it->f, next_face_id)->box
                            == FACE_NO_BOX);