Rails initializers

By default, Rails loads Zeitwerk after the initializers in config/initializers are loaded. Autoloading before Zeitwerk is loaded is now deprecated but because we use a lot of autoloaded constants in our initializers, we had to move the loading of Zeitwerk earlier than these initializers.

A side-effect of this is that in the initializers, config.autoload_paths is already frozen.

To run an initializer before Zeitwerk is loaded, you need put them in config/initializers_before_autoloader. Ruby files in this folder are loaded in alphabetical order just like the default Rails initializers.

Some examples where you would need to do this are:

  1. Modifying Rails’ config.autoload_paths
  2. Changing configuration that Zeitwerk uses, for example, inflections

Database connections in initializers

Ideally, database connections are not opened from Rails initializers. Opening a database connection (for example, checking the database exists, or making a database query) from an initializer means that tasks like db:drop, and db:test:prepare will fail because an active session prevents the database from being dropped.

To help detect when database connections are opened from initializers, we now warn in stderr. For example:

DEPRECATION WARNING: Database connection should not be called during initializers (called from block in <module:HasVariable> at app/models/concerns/ci/has_variable.rb:22)

If you wish to print out the full backtrace, set the DEBUG_INITIALIZER_CONNECTIONS environment variable.