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)

1 files changed, 19 insertions, 5 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 08c6927052c..bfc48e36a99 100644
--- 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,