notmuch.el: Add command to (a)rchive a thread from notmuch-show mode.

This is our first race-free implementation of archive-thread! It
acts only on the messages explcitly contained in the buffer, not
on an entire thread ID, so it's safe in the face of new messages
have been delivered for this thread since the view was made.

notmuch.el

@@ -40,10 +40,11 @@
     ; Will be much preferable to switch to direct manipulation for
     ; toggling visibility of these components. Probably using
     ; overlays-at to query and manipulate the current overlay.
+    (define-key map "a" 'notmuch-show-archive-thread)
     (define-key map "b" 'notmuch-show-toggle-body-read-visible)
     (define-key map "c" 'notmuch-show-toggle-citations-visible)
     (define-key map "h" 'notmuch-show-toggle-headers-visible)
-    (define-key map "n" 'notmuch-show-next-message)
+    (define-key map "n" 'notmuch-show-mark-read-then-next-message)
     (define-key map "p" 'notmuch-show-previous-message)
     (define-key map "q" 'kill-this-buffer)
     (define-key map "s" 'notmuch-show-toggle-signatures-visible)
@@ -108,13 +109,28 @@
   (notmuch-call-notmuch-process "tag" (concat "-" tag) (concat "id:" (notmuch-show-get-message-id)))
   (notmuch-show-set-tags (delete tag (notmuch-show-get-tags))))
 
+(defun notmuch-show-archive-thread ()
+  "Archive each message currrently shown by removing the \"inbox\" tag from each.
+
+This command is safe from any race condition of new messages
+being delivered to the same thread. It does not archive the
+entire thread, but only the messages shown in the current
+buffer."
+  (interactive)
+  (save-excursion
+    (goto-char (point-min))
+    (while (not (eobp))
+      (notmuch-show-remove-tag "inbox")
+      (if (not (eobp))
+	  (forward-char))
+      (if (not (re-search-forward notmuch-show-message-begin-regexp nil t))
+	  (goto-char (point-max))))))
+
 (defun notmuch-show-next-message ()
   "Advance point to the beginning of the next message in the buffer.
 
-Before moving, also remove the \"unread\" tag from the current message."
+Does nothing if already on the last message."
   (interactive)
-  (if (member "unread" (notmuch-show-get-tags))
-      (notmuch-show-remove-tag "unread"))
   ; First, ensure we get off the current message marker
   (if (not (eobp))
       (forward-char))
@@ -135,7 +151,9 @@ Before moving, also remove the \"unread\" tag from the current message."
   (recenter 0))
 
 (defun notmuch-show-previous-message ()
-  "Advance point to the beginning of the previous message in the buffer."
+  "Backup to the beginning of the previous message in the buffer.
+
+Does nothing if already on the first message in the buffer."
   (interactive)
   ; First, ensure we get off the current message marker
   (if (not (bobp))
@@ -156,6 +174,13 @@ Before moving, also remove the \"unread\" tag from the current message."
   (beginning-of-line)
   (recenter 0))
 
+(defun notmuch-show-mark-read-then-next-message ()
+  "Remove uread tag from current message, then advance to next message."
+  (interactive)
+  (if (member "unread" (notmuch-show-get-tags))
+      (notmuch-show-remove-tag "unread"))
+  (notmuch-show-next-message))
+
 (defun notmuch-show-markup-citations-region (beg end)
   (goto-char beg)
   (beginning-of-line)