Add Sevencop/MapMethodChain cop

README.md

@@ -32,6 +32,7 @@ Note that all cops are `Enabled: false` by default.
 - [Sevencop/FactoryBotAssociationOption](lib/rubocop/cop/sevencop/factory_bot_association_option.rb)
 - [Sevencop/FactoryBotAssociationStyle](lib/rubocop/cop/sevencop/factory_bot_association_style.rb)
 - [Sevencop/HashElementOrdered](lib/rubocop/cop/sevencop/hash_element_ordered.rb)
+- [Sevencop/MapMethodChain](lib/rubocop/cop/sevencop/map_method_chain.rb)
 - [Sevencop/MethodDefinitionArgumentsMultiline](lib/rubocop/cop/sevencop/method_definition_arguments_multiline.rb)
 - [Sevencop/MethodDefinitionInIncluded](lib/rubocop/cop/sevencop/method_definition_in_included.rb)
 - [Sevencop/MethodDefinitionKeywordArgumentOrdered](lib/rubocop/cop/sevencop/method_definition_keyword_argument_ordered.rb)

config/default.yml

@@ -37,6 +37,12 @@ Sevencop/HashElementOrdered:
   Enabled: false
   Safe: false
 
+Sevencop/MapMethodChain:
+  Description: |
+    Checks if the map method is used in a chain.
+  Enabled: false
+  Safe: false
+
 Sevencop/MethodDefinitionArgumentsMultiline:
   Description: |
     Inserts new lines between method definition arguments.

lib/rubocop/cop/sevencop/map_method_chain.rb

@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Sevencop
+      # Checks if the map method is used in a chain.
+      #
+      # This cop is another version of `Performance/MapMethodChain` cop which has the autocorrection support.
+      # They have decided not to add autocorrection, so we have this cop in case you want to use it.
+      # https://github.com/rubocop/rubocop-performance/issues/436
+      #
+      # @example
+      #   # bad
+      #   array.map(&:foo).map(&:bar)
+      #
+      #   # good
+      #   array.map { |element| element.foo.bar }
+      class MapMethodChain < Base
+        extend AutoCorrector
+
+        include IgnoredNode
+
+        RESTRICT_ON_SEND = %i[map collect].freeze
+
+        # @!method block_pass_with_symbol_arg?(node)
+        def_node_matcher :block_pass_with_symbol_arg?, <<~PATTERN
+          (:block_pass (:sym $_))
+        PATTERN
+
+        def on_send(node)
+          return if part_of_ignored_node?(node)
+          return unless (map_arg = block_pass_with_symbol_arg?(node.first_argument))
+
+          map_args = [map_arg]
+          return unless (begin_of_chained_map_method = find_begin_of_chained_map_method(node, map_args))
+
+          range = begin_of_chained_map_method.loc.selector.begin.join(node.source_range.end)
+          replacement = "#{begin_of_chained_map_method.method_name} { |element| element.#{map_args.join('.')} }"
+          add_offense(
+            range,
+            message: format(
+              'Use `%<replacement>s` instead of `%<method_name>s` method chain.',
+              method_name: begin_of_chained_map_method.method_name,
+              replacement: replacement
+            )
+          ) do |corrector|
+            corrector.replace(range, replacement)
+          end
+
+          ignore_node(node)
+        end
+
+        private
+
+        def find_begin_of_chained_map_method(
+          node,
+          map_args
+        )
+          return unless (chained_map_method = node.receiver)
+          return if !chained_map_method.call_type? || !RESTRICT_ON_SEND.include?(chained_map_method.method_name)
+          return unless (map_arg = block_pass_with_symbol_arg?(chained_map_method.first_argument))
+
+          map_args.unshift(map_arg)
+
+          receiver = chained_map_method.receiver
+
+          return chained_map_method unless receiver&.call_type? && block_pass_with_symbol_arg?(receiver.first_argument)
+
+          find_begin_of_chained_map_method(chained_map_method, map_args)
+        end
+      end
+    end
+  end
+end

lib/sevencop.rb

@@ -8,6 +8,7 @@
 require_relative 'rubocop/cop/sevencop/factory_bot_association_option'
 require_relative 'rubocop/cop/sevencop/factory_bot_association_style'
 require_relative 'rubocop/cop/sevencop/hash_element_ordered'
+require_relative 'rubocop/cop/sevencop/map_method_chain'
 require_relative 'rubocop/cop/sevencop/method_definition_arguments_multiline'
 require_relative 'rubocop/cop/sevencop/method_definition_in_included'
 require_relative 'rubocop/cop/sevencop/method_definition_keyword_argument_ordered'

spec/rubocop/cop/sevencop/map_method_chain_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Sevencop::MapMethodChain, :config do
+  context 'with 2 map method chain' do
+    it 'registers offense' do
+      expect_offense(<<~RUBY)
+        array.map(&:foo).map(&:bar)
+              ^^^^^^^^^^^^^^^^^^^^^ Use `map { |element| element.foo.bar }` instead of `map` method chain.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        array.map { |element| element.foo.bar }
+      RUBY
+    end
+  end
+
+  context 'with 3 map method chain' do
+    it 'registers offense' do
+      expect_offense(<<~RUBY)
+        array&.map(&:foo).map(&:bar).map(&:baz)
+               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `map { |element| element.foo.bar.baz }` instead of `map` method chain.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        array&.map { |element| element.foo.bar.baz }
+      RUBY
+    end
+  end
+end