bbatsov/rubocop

# frozen_string_literal: true

module RuboCop
  module Cop
    module Style
      # Looks for trivial reader/writer methods, that could
      # have been created with the attr_* family of functions automatically.
      # `to_ary`, `to_a`, `to_c`, `to_enum`, `to_h`, `to_hash`, `to_i`, `to_int`, `to_io`,
      # `to_open`, `to_path`, `to_proc`, `to_r`, `to_regexp`, `to_str`, `to_s`, and `to_sym` methods
      # are allowed by default. These are customizable with `AllowedMethods` option.
      #
      # @example
      #   # bad
      #   def foo
      #     @foo
      #   end
      #
      #   def bar=(val)
      #     @bar = val
      #   end
      #
      #   def self.baz
      #     @baz
      #   end
      #
      #   # good
      #   attr_reader :foo
      #   attr_writer :bar
      #
      #   class << self
      #     attr_reader :baz
      #   end
      #
      # @example ExactNameMatch: true (default)
      #   # good
      #   def name
      #     @other_name
      #   end
      #
      # @example ExactNameMatch: false
      #   # bad
      #   def name
      #     @other_name
      #   end
      #
      # @example AllowPredicates: true (default)
      #   # good
      #   def foo?
      #     @foo
      #   end
      #
      # @example AllowPredicates: false
      #   # bad
      #   def foo?
      #     @foo
      #   end
      #
      #   # good
      #   attr_reader :foo
      #
      # @example AllowDSLWriters: true (default)
      #   # good
      #   def on_exception(action)
      #     @on_exception=action
      #   end
      #
      # @example AllowDSLWriters: false
      #   # bad
      #   def on_exception(action)
      #     @on_exception=action
      #   end
      #
      #   # good
      #   attr_writer :on_exception
      #
      # @example IgnoreClassMethods: false (default)
      #   # bad
      #   def self.foo
      #     @foo
      #   end
      #
      #   # good
      #   class << self
      #     attr_reader :foo
      #   end
      #
      # @example IgnoreClassMethods: true
      #   # good
      #   def self.foo
      #     @foo
      #   end
      #
      # @example AllowedMethods: ['allowed_method']
      #   # good
      #   def allowed_method
      #     @foo
      #   end
      class TrivialAccessors < Base
        include AllowedMethods
        extend AutoCorrector

        MSG = 'Use `attr_%<kind>s` to define trivial %<kind>s methods.'

        def on_def(node)
          return if top_level_node?(node)
          return if in_module_or_instance_eval?(node)
          return if ignore_class_methods? && node.defs_type?

          on_method_def(node)
        end
        alias on_defs on_def

        private

        def in_module_or_instance_eval?(node)
          node.each_ancestor(:block, :class, :sclass, :module).each do |pnode|
            case pnode.type
            when :class, :sclass
              return false
            when :module
              return true
            else
              return true if pnode.method?(:instance_eval)
            end
          end
          false
        end

        def on_method_def(node)
          kind = if trivial_reader?(node)
                   'reader'
                 elsif trivial_writer?(node)
                   'writer'
                 end
          return unless kind

          add_offense(node.loc.keyword, message: format(MSG, kind: kind)) do |corrector|
            autocorrect(corrector, node)
          end
        end

        def autocorrect(corrector, node)
          parent = node.parent
          return if parent&.send_type?

          if node.def_type?
            autocorrect_instance(corrector, node)
          elsif node.defs_type? && node.children.first.self_type?
            autocorrect_class(corrector, node)
          end
        end

        def exact_name_match?
          cop_config['ExactNameMatch']
        end

        def allow_predicates?
          cop_config['AllowPredicates']
        end

        def allow_dsl_writers?
          cop_config['AllowDSLWriters']
        end

        def ignore_class_methods?
          cop_config['IgnoreClassMethods']
        end

        def allowed_method_names
          allowed_methods.map(&:to_sym) + [:initialize]
        end

        def dsl_writer?(node)
          !node.assignment_method?
        end

        def trivial_reader?(node)
          looks_like_trivial_reader?(node) && !allowed_method_name?(node) && !allowed_reader?(node)
        end

        def looks_like_trivial_reader?(node)
          !node.arguments? && node.body&.ivar_type?
        end

        def trivial_writer?(node)
          looks_like_trivial_writer?(node) && !allowed_method_name?(node) && !allowed_writer?(node)
        end

        # @!method looks_like_trivial_writer?(node)
        def_node_matcher :looks_like_trivial_writer?, <<~PATTERN
          {(def    _ (args (arg ...)) (ivasgn _ (lvar _)))
           (defs _ _ (args (arg ...)) (ivasgn _ (lvar _)))}
        PATTERN

        def allowed_method_name?(node)
          allowed_method_names.include?(node.method_name) ||
            (exact_name_match? && !names_match?(node))
        end

        def allowed_writer?(node)
          allow_dsl_writers? && dsl_writer?(node)
        end

        def allowed_reader?(node)
          allow_predicates? && node.predicate_method?
        end

        def names_match?(node)
          ivar_name, = *node.body

          node.method_name.to_s.sub(/[=?]$/, '') == ivar_name[1..]
        end

        def trivial_accessor_kind(node)
          if trivial_writer?(node) && !dsl_writer?(node)
            'writer'
          elsif trivial_reader?(node)
            'reader'
          end
        end

        def accessor(kind, method_name)
          "attr_#{kind} :#{method_name.to_s.chomp('=')}"
        end

        def autocorrect_instance(corrector, node)
          kind = trivial_accessor_kind(node)

          return unless names_match?(node) && !node.predicate_method? && kind

          corrector.replace(node, accessor(kind, node.method_name))
        end

        def autocorrect_class(corrector, node)
          kind = trivial_accessor_kind(node)

          return unless names_match?(node) && kind

          indent = ' ' * node.loc.column
          corrector.replace(
            node,
            ['class << self',
             "#{indent}  #{accessor(kind, node.method_name)}",
             "#{indent}end"].join("\n")
          )
        end

        def top_level_node?(node)
          node.parent.nil?
        end
      end
    end
  end
end