Fix display of :box face when overlay strings are around

* src/xdisp.c (reset_box_start_end_flags): New function.
(handle_face_prop): Only set the start_of_box_run_p flag, don't
reset it.
(pop_it): Set the face_box_p flag, if the popped face requires
that, when continuing iteration over buffer text.
(get_next_display_element, next_element_from_display_vector): Only
set the end_of_box_run_p flag, never reset it here.
(set_iterator_to_next): Don't reset the start_of_box_run_p and
end_of_box_run_p flags here.  They are now reset as side effect of
PRODUCE_GLYPHS.
(append_space_for_newline): Restore the end_of_box_run_p flag
after PRODUCE_GLYPHS where we previously didn't reset it.
* src/dispextern.h (PRODUCE_GLYPHS): Call
reset_box_start_end_flags after producing glyphs.
(Bug#40124)

2 files changed, 67 insertions, 29 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index 724aad4227e..08380f1f17f 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -2782,7 +2782,8 @@ struct it
     else                                                \
       produce_glyphs ((IT));                            \
     if ((IT)->glyph_row != NULL)                        \
-      inhibit_free_realized_faces = true;               \
+      inhibit_free_realized_faces =true;                \
+    reset_box_start_end_flags ((IT));                   \
   } while (false)
 
 /* Bit-flags indicating what operation move_it_to should perform.  */
diff --git a/src/xdisp.c b/src/xdisp.c
index 3c594b54add..04fc8aa3c45 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -1020,6 +1020,7 @@ static Lisp_Object calc_line_height_property (struct it *, Lisp_Object,
 static void produce_special_glyphs (struct it *, enum display_element_type);
 static void show_mouse_face (Mouse_HLInfo *, enum draw_glyphs_face);
 static bool coords_in_mouse_face_p (struct window *, int, int);
+static void reset_box_start_end_flags (struct it *);
 
 
 
@@ -1435,6 +1436,29 @@ window_hscroll_limited (struct window *w, struct frame *f)
   return window_hscroll;
 }
 
+/* Reset the box-face start and end flags in the iterator.  This is
+   called after producing glyphs, such that we reset these flags only
+   after producing a glyph with the flag set.  */
+
+static void
+reset_box_start_end_flags (struct it *it)
+{
+  /* Don't reset if we've drawn the glyph in the display margins --
+     those don't count as "produced glyphs".  */
+  if (it->area == TEXT_AREA
+      /* Don't reset if we displayed a fringe bitmap.  */
+      && !(it->what == IT_IMAGE && it->image_id < 0))
+    {
+      /* Don't reset if the face is not a box face: that might mean we
+         are iterating some overlay or display string, and the first
+         character to have the box face is yet to be seen, when we pop
+         the iterator stack. */
+      if (it->face_box_p)
+        it->start_of_box_run_p = false;
+      it->end_of_box_run_p = false;
+    }
+}
+
 /* Return true if position CHARPOS is visible in window W.
    CHARPOS < 0 means return info about WINDOW_END position.
    If visible, set *X and *Y to pixel coordinates of top left corner.
@@ -4315,8 +4339,11 @@ handle_face_prop (struct it *it)
          this is the start of a run of characters with box face,
          i.e. this character has a shadow on the left side.  */
       it->face_id = new_face_id;
-      it->start_of_box_run_p = (new_face->box != FACE_NO_BOX
-                                && (old_face == NULL || !old_face->box));
+      /* Don't reset the start_of_box_run_p flag, only set it if
+         needed.  */
+      if (!(it->start_of_box_run_p && old_face && old_face->box))
+        it->start_of_box_run_p = (new_face->box != FACE_NO_BOX
+                                  && (old_face == NULL || !old_face->box));
       it->face_box_p = new_face->box != FACE_NO_BOX;
     }
 
@@ -6457,7 +6484,16 @@ pop_it (struct it *it)
       it->object = p->u.stretch.object;
       break;
     case GET_FROM_BUFFER:
-      it->object = it->w->contents;
+      {
+        struct face *face = FACE_FROM_ID_OR_NULL (it->f, it->face_id);
+
+        /* Restore the face_box_p flag, since it could have been
+           overwritten by the face of the object that we just finished
+           displaying.  */
+        if (face)
+          it->face_box_p = face->box != FACE_NO_BOX;
+        it->object = it->w->contents;
+      }
       break;
     case GET_FROM_STRING:
       {
@@ -7586,9 +7622,8 @@ get_next_display_element (struct it *it)
                   /* If the box comes from face properties in a
                      display string, check faces in that string.  */
                   int string_face_id = face_after_it_pos (it);
-                  it->end_of_box_run_p
-                    = (FACE_FROM_ID (it->f, string_face_id)->box
-                       == FACE_NO_BOX);
+                  if (FACE_FROM_ID (it->f, string_face_id)->box == FACE_NO_BOX)
+                    it->end_of_box_run_p = true;
                 }
               /* Otherwise, the box comes from the underlying face.
                  If this is the last string character displayed, check
@@ -7657,9 +7692,9 @@ get_next_display_element (struct it *it)
                                                        CHARPOS (pos), 0,
                                                        &ignore, face_id,
                                                        false, 0);
-                          it->end_of_box_run_p
-                            = (FACE_FROM_ID (it->f, next_face_id)->box
-                               == FACE_NO_BOX);
+                          if (FACE_FROM_ID (it->f, next_face_id)->box
+                              == FACE_NO_BOX)
+                            it->end_of_box_run_p = true;
                         }
                     }
                   else if (CHARPOS (pos) >= ZV)
@@ -7672,9 +7707,9 @@ get_next_display_element (struct it *it)
                                                  CHARPOS (pos)
                                                  + TEXT_PROP_DISTANCE_LIMIT,
                                                  false, -1, 0);
-                      it->end_of_box_run_p
-                        = (FACE_FROM_ID (it->f, next_face_id)->box
-                           == FACE_NO_BOX);
+                      if (FACE_FROM_ID (it->f, next_face_id)->box
+                          == FACE_NO_BOX)
+                        it->end_of_box_run_p = true;
                     }
                 }
             }
@@ -7684,9 +7719,9 @@ get_next_display_element (struct it *it)
       else if (it->method != GET_FROM_DISPLAY_VECTOR)
         {
           int face_id = face_after_it_pos (it);
-          it->end_of_box_run_p
-            = (face_id != it->face_id
-               && FACE_FROM_ID (it->f, face_id)->box == FACE_NO_BOX);
+          if (face_id != it->face_id
+              && FACE_FROM_ID (it->f, face_id)->box == FACE_NO_BOX)
+            it->end_of_box_run_p = true;
         }
     }
   /* If we reached the end of the object we've been iterating (e.g., a
@@ -7723,10 +7758,6 @@ get_next_display_element (struct it *it)
 void
 set_iterator_to_next (struct it *it, bool reseat_p)
 {
-  /* Reset flags indicating start and end of a sequence of characters
-     with box.  Reset them at the start of this function because
-     moving the iterator to a new position might set them.  */
-  it->start_of_box_run_p = it->end_of_box_run_p = false;
 
   switch (it->method)
     {
@@ -8138,9 +8169,9 @@ next_element_from_display_vector (struct it *it)
             }
         }
       next_face = FACE_FROM_ID_OR_NULL (it->f, next_face_id);
-      it->end_of_box_run_p = (this_face && this_face->box != FACE_NO_BOX
-                              && (!next_face
-                                  || next_face->box == FACE_NO_BOX));
+      if (this_face && this_face->box != FACE_NO_BOX
+          && (!next_face || next_face->box == FACE_NO_BOX))
+        it->end_of_box_run_p = true;
       it->face_box_p = this_face && this_face->box != FACE_NO_BOX;
     }
   else
@@ -21485,6 +21516,8 @@ append_space_for_newline (struct it *it, bool default_face_p)
 
       const int indicator_column =
         fill_column_indicator_column (it, char_width);
+      int saved_end_of_box_run = it->end_of_box_run_p;
+      bool should_keep_end_of_box_run = false;
 
       if (it->current_x == indicator_column)
         {
@@ -21507,14 +21540,18 @@ append_space_for_newline (struct it *it, bool default_face_p)
              have the end_of_box_run_p flag set for it, so there's no
              need for the appended newline glyph to have that flag
              set.  */
-          if (it->glyph_row->reversed_p
-              /* But if the appended newline glyph goes all the way to
-                 the end of the row, there will be no stretch glyph,
-                 so leave the box flag set.  */
-              && saved_x + FRAME_COLUMN_WIDTH (it->f) < it->last_visible_x)
-            it->end_of_box_run_p = false;
+          if (!(it->glyph_row->reversed_p
+                /* But if the appended newline glyph goes all the way to
+                   the end of the row, there will be no stretch glyph,
+                   so leave the box flag set.  */
+                && saved_x + FRAME_COLUMN_WIDTH (it->f) < it->last_visible_x))
+            should_keep_end_of_box_run = true;
         }
       PRODUCE_GLYPHS (it);
+      /* Restore the end_of_box_run_p flag which was reset by
+         PRODUCE_GLYPHS.  */
+      if (should_keep_end_of_box_run)
+        it->end_of_box_run_p = saved_end_of_box_run;
 #ifdef HAVE_WINDOW_SYSTEM
       if (FRAME_WINDOW_P (it->f))
         {