[PATCH 1/2] emacs: Handle all face forms when combining faces

[Austin Clements <amdragon@MIT.EDU>]

Previously, notmuch-combine-face-text-property assumed that any
existing face properties of the modified text were already in face
list form.  This was true as long as it was the only function
manipulating faces (since it always produced a list form face), but if
anything else has manipulated the face, it was more likely to be
either a face name or a face plist.  It also didn't correctly handle
face lists as arguments, even though the doc string claimed it did.

This patch fixes notmuch-combine-face-text-property to handle all face
forms correctly by canonicalizing both the argument face and the
existing faces into list form.  This also means we can set the face to
a simpler non-list form if there's no existing face.
---
 emacs/notmuch-lib.el |   27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
index d78bcf8..ad2816d 100644
--- a/emacs/notmuch-lib.el
+++ b/emacs/notmuch-lib.el
@@ -301,6 +301,16 @@ current buffer, if possible."
   (loop for (key value . rest) on plist by #'cddr
 	collect (cons (intern (substring (symbol-name key) 1)) value)))
 
+(defun notmuch-face-ensure-list-form (face)
+  "Return FACE in face list form.
+
+If FACE is already a face list, it will be returned as-is.  If
+FACE is a face name or face plist, it will be returned as a
+single element face list."
+  (if (and (listp face) (not (keywordp (car face))))
+      face
+    (list face)))
+
 (defun notmuch-combine-face-text-property (start end face)
   "Combine FACE into the 'face text property between START and END.
 
@@ -309,11 +319,20 @@ and END.  Attributes specified by FACE take precedence over
 existing attributes.  FACE must be a face name (a symbol or
 string), a property list of face attributes, or a list of these."
 
-  (let ((pos start))
+  ;; A face property can have three forms: a face name (a string or
+  ;; symbol), a property list, or a list of these two forms.  In the
+  ;; list case, the faces will be combined, with the earlier faces
+  ;; taking precedent.  Here we canonicalize everything to list form
+  ;; to make it easy to combine.
+  (let ((pos start)
+	(face-list (notmuch-face-ensure-list-form face)))
     (while (< pos end)
-      (let ((cur (get-text-property pos 'face))
-	    (next (next-single-property-change pos 'face nil end)))
-	(put-text-property pos next 'face (cons face cur))
+      (let* ((cur (get-text-property pos 'face))
+	     (cur-list (notmuch-face-ensure-list-form cur))
+	     (new (cond ((null cur-list) face)
+			(t (append face-list cur-list))))
+	     (next (next-single-property-change pos 'face nil end)))
+	(put-text-property pos next 'face new)
 	(setq pos next)))))
 
 (defun notmuch-logged-error (msg &optional extra)
-- 
1.7.10.4