no_let.rb

# frozen_string_literal: true

# TODO: when finished, run `rake generate_cops_documentation` to update the docs
module RuboCop
  module Cop
    module RSpec
      # Checks for usage of `let` blocks in specs.
      #
      # 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/NoLet:
      #   #   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 NoLet < Cop
        MSG = 'Avoid using `%<method>s` ' \
              '– use a method call or local variable instead.'

        def_node_matcher :let?, <<~PATTERN
          (send nil? :let ...)
        PATTERN

        def_node_matcher :subject?, <<~PATTERN
          (send nil? :subject ...)
        PATTERN

        def on_send(node)
          if subject?(node) && !allow_subject?
            add_offense(node, message: format(MSG, method: 'subject'))
          elsif let?(node)
            add_offense(node, message: format(MSG, method: 'let'))
          end
        end

        private

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