Use different labels for wash buttons when text is visible or hidden.

Before the change, citation and signature wash buttons used the
same label in both visible and hidden states.  Sometimes it is
very convenient when you can determine if the text is hidden or
shown without reading the context and/or clicking the button.
The patch makes it easy to see if the text is shown or hidden by
explicitly saying what the button does (shows or hides the text).

emacs/notmuch-wash.el

@@ -35,16 +35,26 @@
   "\\(^[[:space:]]*>.*\n\\)+"
   "Pattern to match citation lines.")
 
-(defvar notmuch-wash-signature-button-format
+(defvar notmuch-wash-button-signature-hidden-format
-  "[ %d-line signature. Click/Enter to toggle visibility. ]"
+  "[ %d-line signature. Click/Enter to show. ]"
   "String used to construct button text for hidden signatures.
 Can use up to one integer format parameter, i.e. %d")
 
-(defvar notmuch-wash-citation-button-format
+(defvar notmuch-wash-button-signature-visible-format
-  "[ %d more citation lines. Click/Enter to toggle visibility. ]"
+  "[ %d-line signature. Click/Enter to hide. ]"
+  "String used to construct button text for visible signatures.
+Can use up to one integer format parameter, i.e. %d")
+
+(defvar notmuch-wash-button-citation-hidden-format
+  "[ %d more citation lines. Click/Enter to show. ]"
   "String used to construct button text for hidden citations.
 Can use up to one integer format parameter, i.e. %d")
 
+(defvar notmuch-wash-button-citation-visible-format
+  "[ %d more citation lines. Click/Enter to hide. ]"
+  "String used to construct button text for visible citations.
+Can use up to one integer format parameter, i.e. %d")
+
 (defvar notmuch-wash-signature-lines-max 12
   "Maximum length of signature that will be hidden by default.")
 
@@ -69,6 +79,16 @@ collapse the remaining lines into a button.")
     (if (invisible-p invis-spec)
 	(remove-from-invisibility-spec invis-spec)
       (add-to-invisibility-spec invis-spec)))
+  (let* ((new-start (button-start cite-button))
+	 (overlay (button-get cite-button 'overlay))
+	 (button-label (notmuch-wash-button-label overlay))
+	 (inhibit-read-only t))
+    (save-excursion
+      (goto-char new-start)
+      (insert button-label)
+      (let ((old-end (button-end cite-button)))
+	(move-overlay cite-button new-start (point))
+	(delete-region (point) old-end))))
   (force-window-update)
   (redisplay t))
 
@@ -88,13 +108,21 @@ collapse the remaining lines into a button.")
 (defun notmuch-wash-region-isearch-show (overlay)
   (remove-from-invisibility-spec (overlay-get overlay 'invisible)))
 
-(defun notmuch-wash-region-to-button (beg end type prefix button-text)
+(defun notmuch-wash-button-label (overlay)
+  (let* ((type (overlay-get overlay 'type))
+	 (invis-spec (overlay-get overlay 'invisible))
+	 (state (if (invisible-p invis-spec) "hidden" "visible"))
+	 (label-format (symbol-value (intern-soft (concat "notmuch-wash-button-"
+							  type "-" state "-format"))))
+	 (lines-count (count-lines (overlay-start overlay) (overlay-end overlay))))
+    (format label-format lines-count)))
+
+(defun notmuch-wash-region-to-button (beg end type prefix)
   "Auxilary function to do the actual making of overlays and buttons
 
 BEG and END are buffer locations. TYPE should a string, either
 \"citation\" or \"signature\". PREFIX is some arbitrary text to
-insert before the button, probably for indentation.  BUTTON-TEXT
+insert before the button, probably for indentation."
-is what to put on the button."
 
   ;; This uses some slightly tricky conversions between strings and
   ;; symbols because of the way the button code works. Note that
@@ -108,12 +136,14 @@ is what to put on the button."
     (add-to-invisibility-spec invis-spec)
     (overlay-put overlay 'invisible invis-spec)
     (overlay-put overlay 'isearch-open-invisible #'notmuch-wash-region-isearch-show)
+    (overlay-put overlay 'type type)
     (goto-char (1+ end))
     (save-excursion
       (goto-char (1- beg))
       (insert prefix)
-      (insert-button button-text
+      (insert-button (notmuch-wash-button-label overlay)
 		     'invisibility-spec invis-spec
+		     'overlay overlay
 		     :type button-type))))
 
 (defun notmuch-wash-excerpt-citations (depth)
@@ -136,11 +166,7 @@ is what to put on the button."
 	  (forward-line (- notmuch-wash-citation-lines-suffix))
 	  (notmuch-wash-region-to-button
 	   hidden-start (point-marker)
-	   "citation" "\n"
+	   "citation" "\n")))))
-	   (format notmuch-wash-citation-button-format
-		   (- cite-lines
-		      notmuch-wash-citation-lines-prefix
-		      notmuch-wash-citation-lines-suffix)))))))
   (if (and (not (eobp))
 	   (re-search-forward notmuch-wash-signature-regexp nil t))
       (let* ((sig-start (match-beginning 0))
@@ -154,8 +180,7 @@ is what to put on the button."
 	      (overlay-put (make-overlay sig-start-marker sig-end-marker) 'face 'message-cited-text-face)
 	      (notmuch-wash-region-to-button
 	       sig-start-marker sig-end-marker
-	       "signature" "\n"
+	       "signature" "\n"))))))
-	       (format notmuch-wash-signature-button-format sig-lines)))))))
 
 ;;