There are many new features and enhancements in Rails 7.1, which was recently released. The addition of a new configuration method, config.autoload_lib(ignore:), is one of the features.

In Rails, the lib directory is frequently used for custom modules, utility classes, and other shared pieces of code. But as the framework has evolved, there have been modifications to how Rails handles the lib directory.

By default, engines or apps do not include the lib directory in their autoload paths.

This configuration enables us to autoload files in the lib sub-directory and it allows us to ignore specific folders in the lib directory as well.

Autoload Paths in Early Versions of Rails:

Prior to Rails 3, the lib directory was autoloaded by default in earlier versions of Rails. When classes or modules are referred to in our application, Rails will automatically search the folders listed in autoloaded paths to locate and load those references. As a result, any Ruby files added to the lib directory would be loaded immediately in both development and production environments.

Including lib in the autoload paths appeared to be convenient, but it was not an ideal solution when apps were operating in production mode. Rails uses eager loading, in which all classes and modules are loaded in advance for better performance. It wasn’t always suitable for lib files, such as “generators,” meant for development, not automatic loading in a running application.

Starting with Rails 3, the lib directory was removed from the standard autoload paths. As a result, Rails won’t load classes or modules from the lib directory by default. Check Rails 3.0 general configuration and Rails 2.3 configuration

Before:

Starting with Rails version 6, we can pass the lib path to the autoload_paths and eager_load_paths methods. This will load all the classes and modules inside the lib sub-directory.

Under the hood, the autoloader paths uses Zeitwerk which loads the classes and modules in the project on-demand without calling the require.

The autoload_paths loads every sub-directory in the app directory by default except assets, javascript, and views.

We can ignore any sub-directories in the lib directory that do not contain Ruby files by passing their paths to Rails.autoloaders.main.ignore.

# config/application.rb

config.autoload_paths << "#{Rails.root}/lib"
config.eager_load_paths << "#{Rails.root}/lib"

%w(assets generators tasks templates).each do |subdir|
  Rails.autoloaders.main.ignore("#{Rails.root}/lib/#{subdir}")
end

After:

From Rails 7.1, config.autoload_lib(ignore:) method adds the lib directory to config.autoload_paths and config.eager_load_paths.

It cannot be used by engines and must be called from config/application.rb or config/environments/*.rb

  # config/application.rb

  config.autoload_lib(ignore: %w(assets tasks))

The config.autoload_lib(ignore:) method also allow us to avoid autoloading or eager loading specific sub-directories inside the lib directory. We can specify the sub-directory names that need to be ignored using the ignore keyword argument, as shown in the above example. In this case, the assets and tasks sub-directories inside the lib directory will not be autoloaded.