memoized_helpers_in_example_group.rb

# frozen_string_literal: true

module RuboCop
  module Cop
    module RSpec
      # Checks for over-usage of `let` and `subject` blocks in example groups.
      #
      # The maximum count can be configured.
      # This cop can be configured with the option `AllowSubject` which
      # will configure the cop to only register offenses on explicit calls to
      # `let` and not calls to `subject`
      #
      # @example
      #   # bad
      #   describe MyClass do
      #     let(:foo) { [] }
      #     it { expect(foo).to be_empty }
      #   end
      #
      #   describe MyClass do
      #     subject(:foo) { [] }
      #     it { expect(foo).to be_empty }
      #   end
      #
      #   # good
      #   describe MyClass do
      #     it do
      #       foo = []
      #       expect(foo).to be_empty
      #     end
      #   end
      #
      # @example with AllowSubject configuration
      #
      #   # rubocop.yml
      #   # RSpec/MemoizedHelpersInExampleGroup:
      #   #   AllowSubject: true
      #
      #   # bad
      #   describe MyClass do
      #     let(:foo) { [] }
      #     it { expect(foo).to be_empty }
      #   end
      #
      #   # good
      #   describe MyClass do
      #     subject(:foo) { [] }
      #     it { expect(foo).to be_empty }
      #   end
      #
      #   describe MyClass do
      #     it do
      #       foo = []
      #       expect(foo).to be_empty
      #     end
      #   end
      #
      class MemoizedHelpersInExampleGroup < Cop
        MSG = 'Too many memoized helpers used. [%<count>d/%<max>d]'

        def on_block(node)
          return unless example_group?(node)

          count = count_helpers(node)

          node.each_ancestor(:block) do |ancestor|
            count += count_helpers(ancestor)
          end

          return if count <= max

          add_offense(node, message: format(MSG, count: count, max: max))
        end

        private

        def count_helpers(node)
          example_group = RuboCop::RSpec::ExampleGroup.new(node)
          count = example_group.lets.count
          count += example_group.subjects.count unless allow_subject?
          count
        end

        def max
          cop_config['Max']
        end

        def allow_subject?
          cop_config['AllowSubject']
        end
      end
    end
  end
end