Make nnimap support IMAP namespaces

* lisp/gnus/nnimap.el (nnimap-use-namespaces): Introduce new
server variable.
(nnimap-group-to-imap, nnimap-get-groups): Transform IMAP group
names to Gnus group name by stripping / prefixing personal
namespace prefix.
(nnimap-open-connection-1): Ask server for namespaces and store
them.

* lisp/gnus/nnimap.el (nnimap-request-group-scan)
(nnimap-request-create-group, nnimap-request-delete-group)
(nnimap-request-rename-group, nnimap-request-move-article)
(nnimap-process-expiry-targets)
(nnimap-request-update-group-status)
(nnimap-request-accept-article, nnimap-request-list)
(nnimap-retrieve-group-data-early, nnimap-change-group)
(nnimap-split-incoming-mail): Use nnimap-group-to-imap.
(nnimap-group-to-imap): New function to map Gnus group names to
IMAP folder names.  (Bug#21057)

3 files changed, 79 insertions, 27 deletions

diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index 6793ed2e9f1..6ccb9e55f31 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -14320,6 +14320,12 @@ fetch all textual parts, while leaving the rest on the server.
 If non-@code{nil}, record all @acronym{IMAP} commands in the
 @samp{"*imap log*"} buffer.
 
+@item nnimap-use-namespaces
+If non-@code{nil}, omit the IMAP namespace prefix in nnimap group
+names.  If your IMAP mailboxes are called something like @samp{INBOX}
+and @samp{INBOX.Lists.emacs}, but you'd like the nnimap group names to
+be @samp{INBOX} and @samp{Lists.emacs}, you should enable this option.
+
 @end table
 
 
diff --git a/etc/NEWS b/etc/NEWS
index 21887f5bfd3..0b1e6499f41 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -53,6 +53,13 @@ option --enable-check-lisp-object-type is therefore no longer as
 useful and so is no longer enabled by default in developer builds,
 to reduce differences between developer and production builds.
 
+** Gnus
+
++++
+*** The nnimap backend now has support for IMAP namespaces.
+This feature can be enabled by setting the new 'nnimap-use-namespaces'
+server variable to non-nil.
+
 
 * Startup Changes in Emacs 27.1
 
diff --git a/lisp/gnus/nnimap.el b/lisp/gnus/nnimap.el
index 3b397319272..12892c516a7 100644
--- a/lisp/gnus/nnimap.el
+++ b/lisp/gnus/nnimap.el
@@ -55,6 +55,13 @@
 If nnimap-stream is `ssl', this will default to `imaps'.  If not,
 it will default to `imap'.")
 
+(defvoo nnimap-use-namespaces nil
+  "Whether to use IMAP namespaces.
+If in Gnus your folder names in all start with (e.g.) `INBOX',
+you probably want to set this to t.  The effects of this are
+purely cosmetic, but changing this variable will affect the
+names of your nnimap groups. ")
+
 (defvoo nnimap-stream 'undecided
   "How nnimap talks to the IMAP server.
 The value should be either `undecided', `ssl' or `tls',
@@ -110,6 +117,8 @@ some servers.")
 
 (defvoo nnimap-current-infos nil)
 
+(defvoo nnimap-namespace nil)
+
 (defun nnimap-decode-gnus-group (group)
   (decode-coding-string group 'utf-8))
 
@@ -166,6 +175,19 @@ textual parts.")
 
 (defvar nnimap-inhibit-logging nil)
 
+(defun nnimap-group-to-imap (group)
+  "Convert Gnus group name to IMAP mailbox name."
+  (let* ((inbox (if nnimap-namespace
+                    (substring nnimap-namespace 0 -1) nil)))
+    (utf7-encode
+     (cond ((or (not inbox)
+                (string-equal group inbox))
+            group)
+           ((string-prefix-p "#" group)
+            (substring group 1))
+           (t
+            (concat nnimap-namespace group))) t)))
+
 (defun nnimap-buffer ()
   (nnimap-find-process-buffer nntp-server-buffer))
 
@@ -442,7 +464,8 @@ textual parts.")
              (props (cdr stream-list))
              (greeting (plist-get props :greeting))
              (capabilities (plist-get props :capabilities))
-             (stream-type (plist-get props :type)))
+             (stream-type (plist-get props :type))
+             (server (nnoo-current-server 'nnimap)))
         (when (and stream (not (memq (process-status stream) '(open run))))
           (setq stream nil))
 
@@ -475,9 +498,7 @@ textual parts.")
                                ;; the virtual server name and the address
                                (nnimap-credentials
                                 (gnus-delete-duplicates
-                                 (list
-                                  (nnoo-current-server 'nnimap)
-                                  nnimap-address))
+                                 (list server nnimap-address))
                                 ports
                                 nnimap-user))))
                   (setq nnimap-object nil)
@@ -496,8 +517,17 @@ textual parts.")
                       (dolist (response (cddr (nnimap-command "CAPABILITY")))
                         (when (string= "CAPABILITY" (upcase (car response)))
                           (setf (nnimap-capabilities nnimap-object)
-                                (mapcar #'upcase (cdr response))))))
-                  ;; If the login failed, then forget the credentials
+                                (mapcar #'upcase (cdr response)))))
+                      (when (and nnimap-use-namespaces
+                                 (nnimap-capability "NAMESPACE"))
+                        (erase-buffer)
+                        (nnimap-wait-for-response (nnimap-send-command "NAMESPACE"))
+                        (let ((response (nnimap-last-response-string)))
+                          (when (string-match
+                                 "^\\*\\W+NAMESPACE\\W+((\"\\([^\"\n]+\\)\"\\W+\"\\(.\\)\"))\\W+"
+                                 response)
+                            (setq nnimap-namespace (match-string 1 response))))))
+                  ;; If the login failed, then forget the credentials
                   ;; that are now possibly cached.
                   (dolist (host (list (nnoo-current-server 'nnimap)
                                       nnimap-address))
@@ -837,7 +867,7 @@ textual parts.")
       (with-current-buffer (nnimap-buffer)
         (erase-buffer)
         (let ((group-sequence
-               (nnimap-send-command "SELECT %S" (utf7-encode group t)))
+               (nnimap-send-command "SELECT %S" (nnimap-group-to-imap group)))
               (flag-sequence
                (nnimap-send-command "UID FETCH 1:* FLAGS")))
           (setf (nnimap-group nnimap-object) group)
@@ -870,13 +900,13 @@ textual parts.")
   (setq group (nnimap-decode-gnus-group group))
   (when (nnimap-change-group nil server)
     (with-current-buffer (nnimap-buffer)
-      (car (nnimap-command "CREATE %S" (utf7-encode group t))))))
+      (car (nnimap-command "CREATE %S" (nnimap-group-to-imap group))))))
 
 (deffoo nnimap-request-delete-group (group &optional _force server)
   (setq group (nnimap-decode-gnus-group group))
   (when (nnimap-change-group nil server)
     (with-current-buffer (nnimap-buffer)
-      (car (nnimap-command "DELETE %S" (utf7-encode group t))))))
+      (car (nnimap-command "DELETE %S" (nnimap-group-to-imap group))))))
 
 (deffoo nnimap-request-rename-group (group new-name &optional server)
   (setq group (nnimap-decode-gnus-group group))
@@ -884,7 +914,7 @@ textual parts.")
     (with-current-buffer (nnimap-buffer)
       (nnimap-unselect-group)
       (car (nnimap-command "RENAME %S %S"
-                           (utf7-encode group t) (utf7-encode new-name t))))))
+                           (nnimap-group-to-imap group) (nnimap-group-to-imap new-name))))))
 
 (defun nnimap-unselect-group ()
   ;; Make sure we don't have this group open read/write by asking
@@ -944,7 +974,7 @@ textual parts.")
                                 "UID COPY %d %S"))
                      (result (nnimap-command
                               command article
-                              (utf7-encode internal-move-group t))))
+                              (nnimap-group-to-imap internal-move-group))))
                 (when (and (car result) (not can-move))
                   (nnimap-delete-article article))
                 (cons internal-move-group
@@ -1011,7 +1041,7 @@ textual parts.")
                     "UID MOVE %s %S"
                   "UID COPY %s %S")
                 (nnimap-article-ranges (gnus-compress-sequence articles))
-                (utf7-encode (gnus-group-real-name nnmail-expiry-target) t))
+                (nnimap-group-to-imap (gnus-group-real-name nnmail-expiry-target)))
                (set (if can-move 'deleted-articles 'articles-to-delete) articles))))
       t)
      (t
@@ -1136,7 +1166,7 @@ If LIMIT, first try to limit the search to the N last articles."
                       (unsubscribe "UNSUBSCRIBE")))))
       (when command
         (with-current-buffer (nnimap-buffer)
-          (nnimap-command "%s %S" (cadr command) (utf7-encode group t)))))))
+          (nnimap-command "%s %S" (cadr command) (nnimap-group-to-imap group)))))))
 
 (deffoo nnimap-request-set-mark (group actions &optional server)
   (setq group (nnimap-decode-gnus-group group))
@@ -1191,7 +1221,7 @@ If LIMIT, first try to limit the search to the N last articles."
             (nnimap-unselect-group))
           (erase-buffer)
           (setq sequence (nnimap-send-command
-                          "APPEND %S {%d}" (utf7-encode group t)
+                          "APPEND %S {%d}" (nnimap-group-to-imap group)
                           (length message)))
           (unless nnimap-streaming
             (nnimap-wait-for-connection "^[+]"))
@@ -1271,8 +1301,12 @@ If LIMIT, first try to limit the search to the N last articles."
 
 (defun nnimap-get-groups ()
   (erase-buffer)
-  (let ((sequence (nnimap-send-command "LIST \"\" \"*\""))
-        groups)
+  (let* ((sequence (nnimap-send-command "LIST \"\" \"*\""))
+         (prefix nnimap-namespace)
+         (prefix-len (if prefix (length prefix) nil))
+         (inbox (if prefix
+                    (substring prefix 0 -1) nil))
+         groups)
     (nnimap-wait-for-response sequence)
     (subst-char-in-region (point-min) (point-max)
                           ?\\ ?% t)
@@ -1289,11 +1323,16 @@ If LIMIT, first try to limit the search to the N last articles."
                            (skip-chars-backward " \r\"")
                            (point)))))
         (unless (member '%NoSelect flags)
-          (push (utf7-decode (if (stringp group)
-                                 group
-                               (format "%s" group))
-                             t)
-                groups))))
+          (let* ((group (utf7-decode (if (stringp group) group
+                                       (format "%s" group)) t))
+                 (group (cond ((or (not prefix)
+                                   (equal inbox group))
+                               group)
+                              ((string-prefix-p prefix group)
+                               (substring group prefix-len))
+                              (t
+                               (concat "#" group)))))
+            (push group groups)))))
     (nreverse groups)))
 
 (defun nnimap-get-responses (sequences)
@@ -1319,7 +1358,7 @@ If LIMIT, first try to limit the search to the N last articles."
             (dolist (group groups)
               (setf (nnimap-examined nnimap-object) group)
               (push (list (nnimap-send-command "EXAMINE %S"
-                                               (utf7-encode group t))
+                                               (nnimap-group-to-imap group))
                           group)
                     sequences))
             (nnimap-wait-for-response (caar sequences))
@@ -1391,7 +1430,7 @@ If LIMIT, first try to limit the search to the N last articles."
                    unexist)
               (push
                (list (nnimap-send-command "EXAMINE %S (%s (%s %s))"
-                                          (utf7-encode group t)
+                                          (nnimap-group-to-imap group)
                                           (nnimap-quirk "QRESYNC")
                                           uidvalidity modseq)
                      'qresync
@@ -1413,7 +1452,7 @@ If LIMIT, first try to limit the search to the N last articles."
                 (cl-incf (nnimap-initial-resync nnimap-object))
                 (setq start 1))
               (push (list (nnimap-send-command "%s %S" command
-                                               (utf7-encode group t))
+                                               (nnimap-group-to-imap group))
                           (nnimap-send-command "UID FETCH %d:* FLAGS" start)
                           start group command)
                     sequences))))
@@ -1847,7 +1886,7 @@ Return the server's response to the SELECT or EXAMINE command."
                                       (if read-only
                                           "EXAMINE"
                                         "SELECT")
-                                      (utf7-encode group t))))
+                                      (nnimap-group-to-imap group))))
           (when (car result)
             (setf (nnimap-group nnimap-object) group
                   (nnimap-select-result nnimap-object) result)
@@ -2105,7 +2144,7 @@ Return the server's response to the SELECT or EXAMINE command."
             (dolist (spec specs)
               (when (and (not (member (car spec) groups))
                          (not (eq (car spec) 'junk)))
-                (nnimap-command "CREATE %S" (utf7-encode (car spec) t))))
+                (nnimap-command "CREATE %S" (nnimap-group-to-imap (car spec)))))
             ;; Then copy over all the messages.
             (erase-buffer)
             (dolist (spec specs)
@@ -2121,7 +2160,7 @@ Return the server's response to the SELECT or EXAMINE command."
                                      "UID MOVE %s %S"
                                    "UID COPY %s %S")
                                  (nnimap-article-ranges ranges)
-                                 (utf7-encode group t))
+                                (nnimap-group-to-imap group))
                                 ranges)
                           sequences)))))
             ;; Wait for the last COPY response...