mod_blocklist: Add option 'migrate_legacy_blocking' to disable migration from mod_privacy

Tiny performance improvement for new users by skipping this check. Most
servers should have gone trough the migration for all active users long
ago.

As a suitable first step of phasing out this code, we make it possible
to disable it first. Later it can be disabled by default, before finally
the code is deleted.

CHANGES

@@ -33,6 +33,7 @@ TRUNK
 ## Changes
 
 - Support sub-second precision timestamps
+- mod_blocklist: New option 'migrate_legacy_blocking' to disable migration from mod_privacy
 
 ## Removed
 

plugins/mod_blocklist.lua

@@ -54,6 +54,7 @@ local function set_blocklist(username, blocklist)
 end
 
 -- Migrates from the old mod_privacy storage
+-- TODO mod_privacy was removed in 0.10.0, this should be phased out
 local function migrate_privacy_list(username)
 	local legacy_data = module:open_store("privacy"):get(username);
 	if not legacy_data or not legacy_data.lists or not legacy_data.default then return; end
@@ -77,6 +78,13 @@ local function migrate_privacy_list(username)
 	return migrated_data;
 end
 
+if not module:get_option_boolean("migrate_legacy_blocking", true) then
+	migrate_privacy_list = function (username)
+		module:log("debug", "Migrating from mod_privacy disabled, user '%s' will start with a fresh blocklist", username);
+		return nil;
+	end
+end
+
 local function get_blocklist(username)
 	local blocklist = cache2:get(username);
 	if not blocklist then