[PATCH] nnimap: enable additional expunge options (v3)

[Nikolaus Rath <Nikolaus@rath.org>]

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If the IMAP server supports the UID EXPUNGE command, the nnimap backend
currently always expunges deleted articles.

If the IMAP server does not support this command, articles are either
not expunged at all (nnimap-expunge is nil), or ALL articles that are
currently flagged as deleted will be expunged when any one article is
deleted in Gnus.

This patch introduces three new settings for nnimap-expunge:

 * If nnimap-expunge is 'never, deleted articles are marked with the
   IMAP \\Delete flag but not automatically expunged.

 * If nnimap-expunge is 'immediately, deleted articles are immediately
   expunged (this requires the server to support the UID EXPUNGE
   command).

 * If nnimap-expunge is 'on-exit, deleted articles are flagged, and all
   flagged articles are expunged when the group is closed.

Note that none of these behaviors is available with the current settings
(nil / non-nil).

The 'on-exit setting is mostly useful as a safe-guard: as long as the
group is not closed, article deletions are reversal (either by using a
different IMAP client, or by exiting Gnus without updating the summary
buffer).

The 'never setting is not (yet) very useful because Gnus does not
distinguish between deleted articles and regular articles in the summary
buffer. However, this will be addressed by a separate patch.

Changes in v2:

  * Made first line of docstring a complete sentence.

Changes in v3:

  * Correctly handle multiple active nnimap backends.

Thanks for considering,
-Nikolaus

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diff --git a/nnimap.el b/nnimap.el
--- a/nnimap.el
+++ b/nnimap.el
@@ -103,10 +103,21 @@
 Possible choices are nil (use default methods), `anonymous',
 `login', `plain' and `cram-md5'.")
 
-(defvoo nnimap-expunge t
-  "If non-nil, expunge articles after deleting them.
-This is always done if the server supports UID EXPUNGE, but it's
-not done by default on servers that doesn't support that command.")
+(defvoo nnimap-expunge 'on-exit
+  "When to expunge deleted messages.
+If 'never, deleted articles are marked with the IMAP \\Delete
+flag but not automatically expunged. If 'immediately, deleted
+articles are immediately expunged (this requires the server to
+support the UID EXPUNGE command). If 'on-exit, deleted articles
+are flagged, and all flagged articles are expunged when the
+group is closed.
+
+For backwards compatibility, this variable may also be set to t
+or nil. If the server supports UID EXPUNGE, both t and nil are
+equivalent to 'immediately. If the server does not support UID
+EXPUNGE nil is equivalent to 'never, while t will immediately
+expunge ALL articles that are currently flagged as deleted
+(i.e., potentially not only the article that was just deleted).")
 
 (defvoo nnimap-streaming t
   "If non-nil, try to use streaming commands with IMAP servers.
@@ -865,7 +876,11 @@
     (nreverse articles)))
 
 (deffoo nnimap-close-group (group &optional server)
-  t)
+  (when (eq nnimap-expunge 'on-exit)
+    (nnoo-change-server 'nnimap server nil)
+    (with-current-buffer (nnimap-buffer)
+      (nnimap-wait-for-response
+       (nnimap-send-command "EXPUNGE")))))
 
 (deffoo nnimap-request-move-article (article group server accept-form
 					     &optional last internal-move-group)
@@ -910,8 +925,7 @@
     articles)
    ((and force
 	 (eq nnmail-expiry-target 'delete))
-    (unless (nnimap-delete-article (gnus-compress-sequence articles))
-      (nnheader-message 7 "Article marked for deletion, but not expunged."))
+    (nnimap-delete-article (gnus-compress-sequence articles))
     nil)
    (t
     (let ((deletable-articles
@@ -1027,21 +1041,36 @@
             (when (and limit number-of-article)
               (nnimap-find-article-by-message-id group server message-id))))))))
 
-(defun nnimap-delete-article (articles)
+(defun nnimap-delete-article (articles &optional sync)
+  "Delete ARTICLES.
+
+If sync is non-nil, wait for server response."
   (with-current-buffer (nnimap-buffer)
     (nnimap-command "UID STORE %s +FLAGS.SILENT (\\Deleted)"
 		    (nnimap-article-ranges articles))
+    (let ((sequence
     (cond
-     ((nnimap-capability "UIDPLUS")
+            ((eq nnimap-expunge 'immediately)
+             (if (nnimap-capability "UIDPLUS")
       (nnimap-command "UID EXPUNGE %s"
 		      (nnimap-article-ranges articles))
-      t)
+               (nnheader-message 3 (concat "nnimap-expunge set to 'immediately, but "
+                                           "server doesn't support UIDPLUS"))))
+
+            ((memq nnimap-expunge '(on-exit never)) nil)
+
+            ((nnimap-capability "UIDPLUS")
+             (nnimap-command "UID EXPUNGE %s"
+                             (nnimap-article-ranges articles)))
+
      (nnimap-expunge
-      (nnimap-command "EXPUNGE")
-      t)
-     (t (gnus-message 7 (concat "nnimap: nnimap-expunge is not set and the "
-                                "server doesn't support UIDPLUS, so we won't "
-                                "delete this article now"))))))
+             (nnimap-command "EXPUNGE"))
+
+            (t
+             (nnheader-message 7 "Article marked for deletion, but not expunged.")))))
+
+      (if (and sync sequence)
+          (nnimap-wait-for-response sequence)))))
 
 (deffoo nnimap-request-scan (&optional group server)
   (when group
@@ -2043,27 +2072,9 @@
 	      (nnimap-wait-for-response (caar sequences))
 	      ;; And then mark the successful copy actions as deleted,
 	      ;; and possibly expunge them.
-	      (nnimap-mark-and-expunge-incoming
-	       (nnimap-parse-copied-articles sequences)))
-            (nnimap-mark-and-expunge-incoming junk-articles)))))))
-
-(defun nnimap-mark-and-expunge-incoming (range)
-  (when range
-    (setq range (nnimap-article-ranges range))
-    (erase-buffer)
-    (let ((sequence
-	   (nnimap-send-command
-	    "UID STORE %s +FLAGS.SILENT (\\Deleted)" range)))
-      (cond
-       ;; If the server supports it, we now delete the message we have
-       ;; just copied over.
-       ((nnimap-capability "UIDPLUS")
-	(setq sequence (nnimap-send-command "UID EXPUNGE %s" range)))
-       ;; If it doesn't support UID EXPUNGE, then we only expunge if the
-       ;; user has configured it.
-       (nnimap-expunge
-	(setq sequence (nnimap-send-command "EXPUNGE"))))
-      (nnimap-wait-for-response sequence))))
+              (nnimap-delete-article
+               (nnimap-parse-copied-articles sequences) t))
+            (nnimap-delete-article junk-articles t)))))))
 
 (defun nnimap-parse-copied-articles (sequences)
   (let (sequence copied range)