rubocop/rubocop · error · ArgumentError

Passing a project root directory to `inject_defaults!` is no

Error message

Passing a project root directory to `inject_defaults!` is no longer supported.

What it means

`RuboCop::ConfigLoader.inject_defaults!` merges a plugin's `default.yml` into RuboCop's default configuration. Older plugin ecosystems passed the gem's project root directory; the API now requires the exact YAML file path. Passing a directory first prints a deprecation warning, then raises `ArgumentError`. It is a testing/documentation API — with `rubocop/rspec/support` it is usually unneeded.

Source

Thrown at lib/rubocop/config_loader.rb:166

      def default_configuration
        @default_configuration ||= begin
          print 'Default ' if debug?
          load_file(DEFAULT_FILE)
        end
      end

      # This API is primarily intended for testing and documenting plugins.
      # When testing a plugin using `rubocop/rspec/support`, the plugin is loaded automatically,
      # so this API is usually not needed. It is intended to be used only when implementing tests
      # that do not use `rubocop/rspec/support`.
      def inject_defaults!(config_yml_path)
        if Pathname(config_yml_path).directory?
          warn Rainbow(<<~MESSAGE).yellow, uplevel: 1
            Use config YAML file path instead of project root directory.
            e.g., `path/to/config/default.yml`
          MESSAGE
          raise ArgumentError,
                'Passing a project root directory to `inject_defaults!` is no longer supported.'
        end

        path = config_yml_path.to_s
        hash = ConfigLoader.load_yaml_configuration(path)
        config = Config.new(hash, path).tap(&:make_excludes_absolute)

        @default_configuration = ConfigLoader.merge_with_default(config, path)
      end

      # Returns the path RuboCop inferred as the root of the project. No file
      # searches will go past this directory.
      # @deprecated Use `RuboCop::ConfigFinder.project_root` instead.
      def project_root
        warn Rainbow(<<~WARNING).yellow, uplevel: 1
          `RuboCop::ConfigLoader.project_root` is deprecated and will be removed in RuboCop 2.0. \
          Use `RuboCop::ConfigFinder.project_root` instead.
        WARNING

View on GitHub (pinned to ea712edf2b)

Solutions

Pass the full path to the YAML file: `RuboCop::ConfigLoader.inject_defaults!(File.join(__dir__, 'config', 'default.yml'))`.
If the call lives in a third-party plugin gem, upgrade it to a release compatible with current RuboCop.
If your specs use `rubocop/rspec/support`, delete the `inject_defaults!` call entirely — the plugin loads automatically.
The deprecation warning printed before the raise shows the exact expected form; mirror it.

Example fix

# before
RuboCop::ConfigLoader.inject_defaults!(File.expand_path(__dir__))

# after
RuboCop::ConfigLoader.inject_defaults!(File.join(__dir__, 'config', 'default.yml'))

Defensive patterns

Strategy: type-guard

Validate before calling

path = File.expand_path('config/default.yml', __dir__)
raise ArgumentError, 'pass the YAML file, not a directory' if File.directory?(path)
raise ArgumentError, 'missing default.yml' unless File.file?(path)
RuboCop::ConfigLoader.inject_defaults!(path)

Type guard

def defaults_yaml_path?(path)
  path = Pathname(path)
  path.file? && path.extname == '.yml'
end

Try / catch

begin
  RuboCop::ConfigLoader.inject_defaults!(config_path)
rescue ArgumentError => e
  raise if e.message !~ /project root directory/
  # retry with the YAML file inside the passed directory
  RuboCop::ConfigLoader.inject_defaults!(File.join(config_path, 'config', 'default.yml'))
end

Prevention

Always build the path to `config/default.yml` explicitly; never pass a directory to inject_defaults!.
Prefer `rubocop/rspec/support` in extension specs — it loads plugins automatically and removes the need for inject_defaults!.
Read the deprecation warning output; RuboCop prints the exact expected call form before raising.
When maintaining a plugin, add a spec that exercises the support setup so API changes fail your build first.

When it happens

Trigger: Calling `RuboCop::ConfigLoader.inject_defaults!(File.expand_path(__dir__))` or `inject_defaults!(gem_root)` (a directory) instead of `inject_defaults!('path/to/config/default.yml')`; old README examples from rubocop-extension gems copied into a new plugin.

Common situations: Maintaining a rubocop plugin (e.g. rubocop-foo with its own cops) whose spec support predates the API change; upgrading RuboCop in a gem that still injects defaults via the directory convention.

Related errors

AI-assisted analysis of rubocop/rubocop@ea712edf2b (2026-08-21). Data as JSON: /api/errors/ae21ba7a12a11a79. Report an issue: GitHub.