Added RuboCop cops for checking DB migrationsmigration-cops

There are currently two cops for this:

* Migration/AddIndex: checks if indexes are added concurrently
* Migration/ColumnWithDefault: checks if columns with default values are
  added in a concurrent manner

Both cops are fairly simple and make no attempt at correcting the code
as this is quite hard to do (e.g. modifications may need to be applied
in various places in the same file). They however should provide enough
to catch people ignoring the comments in generated migrations telling
them to use add_concurrent_index or add_column_with_default.

1 files changed, 10 insertions, 0 deletions

diff --git a/rubocop/migration_helpers.rb b/rubocop/migration_helpers.rb
new file mode 100644
index 00000000000..3160a784a04
--- /dev/null
+++ b/rubocop/migration_helpers.rb
@@ -0,0 +1,10 @@
+module RuboCop
+  # Module containing helper methods for writing migration cops.
+  module MigrationHelpers
+    # Returns true if the given node originated from the db/migrate directory.
+    def in_migration?(node)
+      File.dirname(node.location.expression.source_buffer.name).
+        end_with?('db/migrate')
+    end
+  end
+end