bug#19912: facemenu-add-face: does not handle 'face being set to a property list

[Ivan Shmakov]

        Please consider the (once again) revised patch MIMEd.

        * lisp/faces.el (face-list-p): Split from face-at-point.
        (face-at-point): Use it.
        * lisp/facemenu.el (facemenu-add-face): Likewise.  (Bug#19912)

        Unless there be objections, I hope to push this new change
        to ‘master’ within the next day or two.

-- 
FSF associate member #7257  np. Isle of Avalon — Iron Maiden … B6A0 230E 334A

--- a/lisp/facemenu.el
+++ b/lisp/facemenu.el
@@ -732,7 +732,7 @@ defun facemenu-add-face (face &optional start end)
                                  face
                                (facemenu-active-faces
                                 (cons face
-                                      (if (listp prev)
+                                      (if (face-list-p prev)
                                           prev
                                         (list prev)))
                                 ;; Specify the selected frame
--- a/lisp/faces.el
+++ b/lisp/faces.el
@@ -273,6 +273,17 @@ defun face-nontrivial-p (face &optional frame)
   (not (internal-lisp-face-empty-p face frame)))
 
 
+(defun face-list-p (face-or-list)
+  "True if FACE-OR-LIST is a list of faces.
+Return nil if FACE-OR-LIST is a non-nil atom, or a cons cell whose car
+is either 'foreground-color, 'background-color, or a keyword."
+  ;; The logic of merge_face_ref (xfaces.c) is recreated here.
+  (and (listp face-or-list)
+       (not (memq (car face-or-list)
+                 '(foreground-color background-color)))
+       (not (keywordp (car face-or-list)))))
+
+
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;; Setting face attributes from X resources.
@@ -1922,11 +1933,7 @@ defun face-at-point (&optional thing multiple)
                         (get-char-property (point) 'face))))
       (cond ((facep faceprop)
              (push faceprop faces))
-            ((and (listp faceprop)
-                  ;; Don't treat an attribute spec as a list of faces.
-                  (not (keywordp (car faceprop)))
-                  (not (memq (car faceprop)
-                             '(foreground-color background-color))))
+            ((face-list-p faceprop)
              (dolist (face faceprop)
                (if (facep face)
                    (push face faces))))))