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)

1 files changed, 7 insertions, 0 deletions

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