Make `Migrator.current_version` work without a current database

This is necessary in order to make the processing dependent on
`Migrator.current_version` work even without database.

Context: https://github.com/rails/rails/pull/31135#issuecomment-348404326

1 files changed, 9 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 15e9c09ffb..4d4b0dc67a 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -1053,7 +1053,15 @@ module ActiveRecord
         end
       end
 
-      def current_version(connection = Base.connection)
+      def current_version(connection = nil)
+        if connection.nil?
+          begin
+            connection = Base.connection
+          rescue ActiveRecord::NoDatabaseError
+            return nil
+          end
+        end
+
         get_all_versions(connection).max || 0
       end