remove support for the status_backend configuration option

Stop the run when this option is found. Migrating from the historical plain
text status cache is still supported.

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

docs/offlineimap.txt

@@ -228,10 +228,10 @@ if a mail has been added or deleted on either side.
 The historical status cache is a plain text file that writes out the complete
 file for each single new message (or even changed flag) to a temporary file. If
 you have plenty of files in a folder, this is a few hundred kilo to megabytes
-for each mail and is bound to make things slow. The latest default status cache
+for each mail and is bound to make things slow. The latest status cache
 is sqlite. This saves plenty of disk activity. The sqlite engine and the Python
-sqlite module must be installed. Enable the 'status_backend = plain' setting in
-'offlineimap.conf' for legacy compatibility with versions prior to '6.4.0'.
+sqlite module must be installed. The historical plain status cache is not
+supported anymore.
 +
 If you switch the backend from plain to sqlite, you may want to delete the old
 cache directory in '<metadata>/Account-<account>/LocalStatus' manually (the

offlineimap.conf

@@ -314,14 +314,6 @@ remoterepository = RemoteExample
 #postsynchook = notifysync.sh
 
 
-# This option stands in the [Account Test] section.
-#
-# The historical backend is 'plain' which writes out the state in plain text
-# files. See manual.
-#
-#status_backend = sqlite
-
-
 # This option stands in the [Account Test] section.
 #
 # If you have a limited amount of bandwidth available you can exclude larger

offlineimap/repository/LocalStatus.py

@@ -20,31 +20,37 @@ import os
 from offlineimap.folder.LocalStatus import LocalStatusFolder
 from offlineimap.folder.LocalStatusSQLite import LocalStatusSQLiteFolder
 from offlineimap.repository.Base import BaseRepository
+from offlineimap.error import OfflineImapError
 
 
 class LocalStatusRepository(BaseRepository):
     def __init__(self, reposname, account):
         BaseRepository.__init__(self, reposname, account)
 
-        # class and root for all backends
+        # class and root for all backends.
         self.backends = {}
         self.backends['sqlite'] = {
             'class': LocalStatusSQLiteFolder,
             'root': os.path.join(account.getaccountmeta(), 'LocalStatus-sqlite')
         }
-
         self.backends['plain'] = {
             'class': LocalStatusFolder,
             'root': os.path.join(account.getaccountmeta(), 'LocalStatus')
         }
 
-        # Set class and root for the configured backend
-        self.setup_backend(self.account.getconf('status_backend', 'sqlite'))
+        if self.account.getconf('status_backend', None) is not None:
+            raise OfflineImapError(
+                "the 'status_backend' configuration option is not supported"
+                " anymore; please, remove this configuration option.",
+                OfflineImapError.ERROR.REPO
+            )
+        # Set class and root for sqlite.
+        self.setup_backend('sqlite')
 
         if not os.path.exists(self.root):
             os.mkdir(self.root, 0o700)
 
-        # self._folders is a dict of name:LocalStatusFolders()
+        # self._folders is a dict of name:LocalStatusFolders().
         self._folders = {}
 
     def _instanciatefolder(self, foldername):
@@ -56,10 +62,6 @@ class LocalStatusRepository(BaseRepository):
             self.root = self.backends[backend]['root']
             self.LocalStatusFolderClass = self.backends[backend]['class']
 
-        else:
-            raise SyntaxWarning("Unknown status_backend '%s' for account '%s'"%
-                (backend, self.account.name))
-
     def import_other_backend(self, folder):
         for bk, dic in self.backends.items():
             # Skip folder's own type.