From dd3f2130cf2977cff79101e72cff0b433df1c1c6 Mon Sep 17 00:00:00 2001
From: Eli Zaretskii <eliz@gnu.org>
Date: Fri, 13 Dec 2019 12:29:05 +0200
Subject: [PATCH] A better fix for extension of overlay string's faces

* src/xdisp.c (face_at_pos): Revert previous change that
rejected the underlying face if it failed the filtering
criteria.
* src/xfaces.c (face_at_string_position): Reset the base face's
attribute used for filtering faces if the attribute is t.
(Bug#38563)
---
 src/xdisp.c  | 25 +++++--------------------
 src/xfaces.c |  4 ++++
 2 files changed, 9 insertions(+), 20 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index bb370bbb78f..4ddde1be717 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -4243,26 +4243,11 @@ 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.  */
-	  bool use_default = (it->string_from_prefix_prop_p != 0);
-	  base_face_id = DEFAULT_FACE_ID;
-	  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);
+	  base_face_id = it->string_from_display_prop_p
+	    ? (!NILP (Vface_remapping_alist)
+	       ? lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID)
+	       : DEFAULT_FACE_ID)
+	    : underlying_face_id (it);
 	}
 
       return face_at_string_position (it->w,
diff --git a/src/xfaces.c b/src/xfaces.c
index 54b5f4a94a4..5c347d41e30 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -6445,6 +6445,10 @@ face_at_string_position (struct window *w, Lisp_Object string,
 
   /* Begin with attributes from the base face.  */
   memcpy (attrs, base_face->lface, sizeof attrs);
+  /* Reset the attribute of the base face used as the filter, because
+     otherwise there's no way for faces to be merged to countermand that.  */
+  if (EQ (attrs[attr_filter], Qt))
+    attrs[attr_filter] = Qnil;
 
   /* Merge in attributes specified via text properties.  */
   if (!NILP (prop))
-- 
2.39.2