Fix face extension of overlay strings on buffer text with faces

* src/xdisp.c (face_at_pos): Reject the face returned by
'underlying_face_id' when we are filtering by face attribute,
and that attribute's value fails the filter test.  (Bug#38563)

diff --git a/src/xdisp.c b/src/xdisp.c
index 08c6927052cd775b864ce416e4186583bb74bda6..bfc48e36a995ddb7df15f51ec01022adceddad3c 100644 (file)
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -4243,11 +4243,25 @@ face_at_pos (const struct it *it, enum lface_attribute_index attr_filter)
             the display string do.  This sounds like a design bug,
             but Emacs always did that since v21.1, so changing that
             might be a big deal.  */
-         base_face_id = it->string_from_prefix_prop_p
-           ? (!NILP (Vface_remapping_alist)
-              ? lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID)
-              : DEFAULT_FACE_ID)
-           : underlying_face_id (it);
+         bool use_default = (it->string_from_prefix_prop_p != 0);
+         if (!use_default)
+           {
+             base_face_id = underlying_face_id (it);
+             /* Reject the underlying face, if that face is different
+                from the iterator face, and we filter by attr_filter,
+                and that face's value of the filter attribute is nil
+                or unspecified; use the default face instead.  */
+             struct face *bf = FACE_FROM_ID_OR_NULL (it->f, base_face_id);
+             if (base_face_id != it->base_face_id
+                 && attr_filter > 0
+                 && (NILP (bf->lface[attr_filter])
+                     || EQ (bf->lface[attr_filter], Qunspecified)))
+               use_default = true;
+           }
+         if (use_default)
+           base_face_id = (!NILP (Vface_remapping_alist)
+                           ? lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID)
+                           : DEFAULT_FACE_ID);
        }
 
       return face_at_string_position (it->w,