[PATCH] Use IMAP MOVE extension if available

[Nikolaus Rath <Nikolaus@rath.org>]

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Hello,

Currently Gnus uses a combination of COPY, STORE + EXPUNGE to move
messages from one imap group into another.

The attached patch enables the use of the MOVE command instead if the
server supports it.

Thanks for considering.

(Is this the right place to post patches, or should it go to
bug-gnu-emacs@gnu.org?)

Best,
-Nikolaus

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--- nnimap.el.bak	2015-05-25 11:04:15.671769838 -0700
+++ nnimap.el	2015-05-25 12:58:27.051313588 -0700
@@ -881,17 +882,19 @@
       ;; way.
       (let ((message-id (message-field-value "message-id")))
 	(if internal-move-group
-	    (let ((result
-		   (with-current-buffer (nnimap-buffer)
-		     (nnimap-command "UID COPY %d %S"
-				     article
-				     (utf7-encode internal-move-group t)))))
-	      (when (car result)
-		(nnimap-delete-article article)
-		(cons internal-move-group
-		      (or (nnimap-find-uid-response "COPYUID" (cadr result))
-			  (nnimap-find-article-by-message-id
-			   internal-move-group server message-id
+            (with-current-buffer (nnimap-buffer)
+              (let* ((can-move (nnimap-capability "MOVE"))
+                    (command (if can-move
+                                 "UID MOVE %d %S"
+                               "UID COPY %d %S"))
+                    (result (nnimap-command command article
+                                            (utf7-encode internal-move-group t))))
+                (when (and (car result) (not can-move))
+                  (nnimap-delete-article article))
+                (cons internal-move-group
+                      (or (nnimap-find-uid-response "COPYUID" (cadr result))
+                          (nnimap-find-article-by-message-id
+                           internal-move-group server message-id
                            nnimap-request-articles-find-limit)))))
 	  ;; Move the article to a different method.
 	  (let ((result (eval accept-form)))