Add new Style/BisectedAttrAccessor cop

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#7868](https://github.com/rubocop-hq/rubocop/pull/7868): `Cop::Base` is the new recommended base class for cops. ([@marcandre][])
+* [#8244](https://github.com/rubocop-hq/rubocop/pull/8244): Add new `Style/BisectedAttrAccessor` cop. ([@fatkodima][])
 * [#7458](https://github.com/rubocop-hq/rubocop/issues/7458): Add new `AsciiConstants` option for `Naming/AsciiIdentifiers`. ([@fatkodima][])
 * [#7373](https://github.com/rubocop-hq/rubocop/issues/7373): Add new `Style/RedundantAssignment` cop. ([@fatkodima][])
 * [#8213](https://github.com/rubocop-hq/rubocop/pull/8213): Permit to specify TargetRubyVersion 2.8 (experimental). ([@koic][])

config/default.yml

@@ -2366,6 +2366,13 @@ Style/BeginBlock:
   Enabled: true
   VersionAdded: '0.9'
 
+Style/BisectedAttrAccessor:
+  Description: >-
+                Checks for places where `attr_reader` and `attr_writer`
+                for the same method can be combined into single `attr_accessor`.
+  Enabled: 'pending'
+  VersionAdded: '0.87'
+
 Style/BlockComments:
   Description: 'Do not use block comments.'
   StyleGuide: '#no-block-comments'

docs/modules/ROOT/pages/cops.adoc

@@ -321,6 +321,7 @@ In the following section you find all available cops:
 * xref:cops_style.adoc#styleautoresourcecleanup[Style/AutoResourceCleanup]
 * xref:cops_style.adoc#stylebarepercentliterals[Style/BarePercentLiterals]
 * xref:cops_style.adoc#stylebeginblock[Style/BeginBlock]
+* xref:cops_style.adoc#stylebisectedattraccessor[Style/BisectedAttrAccessor]
 * xref:cops_style.adoc#styleblockcomments[Style/BlockComments]
 * xref:cops_style.adoc#styleblockdelimiters[Style/BlockDelimiters]
 * xref:cops_style.adoc#stylecaseequality[Style/CaseEquality]

docs/modules/ROOT/pages/cops_style.adoc

@@ -446,6 +446,37 @@ BEGIN { test }
 
 * https://rubystyle.guide#no-BEGIN-blocks
 
+== Style/BisectedAttrAccessor
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Pending
+| Yes
+| Yes
+| 0.87
+| -
+|===
+
+This cop checks for places where `attr_reader` and `attr_writer`
+for the same method can be combined into single `attr_accessor`.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+class Foo
+  attr_reader :bar
+  attr_writer :bar
+end
+
+# good
+class Foo
+  attr_accessor :bar
+end
+----
+
 == Style/BlockComments
 
 |===

lib/rubocop.rb

@@ -364,6 +364,7 @@
 require_relative 'rubocop/cop/style/auto_resource_cleanup'
 require_relative 'rubocop/cop/style/bare_percent_literals'
 require_relative 'rubocop/cop/style/begin_block'
+require_relative 'rubocop/cop/style/bisected_attr_accessor'
 require_relative 'rubocop/cop/style/block_comments'
 require_relative 'rubocop/cop/style/block_delimiters'
 require_relative 'rubocop/cop/style/case_equality'

lib/rubocop/cop/style/bisected_attr_accessor.rb

@@ -0,0 +1,121 @@
+# frozen_string_literal: true
+
+require 'set'
+
+module RuboCop
+  module Cop
+    module Style
+      # This cop checks for places where `attr_reader` and `attr_writer`
+      # for the same method can be combined into single `attr_accessor`.
+      #
+      # @example
+      #   # bad
+      #   class Foo
+      #     attr_reader :bar
+      #     attr_writer :bar
+      #   end
+      #
+      #   # good
+      #   class Foo
+      #     attr_accessor :bar
+      #   end
+      #
+      class BisectedAttrAccessor < Cop
+        MSG = 'Combine both accessors into `attr_accessor :%<name>s`.'
+
+        def on_class(class_node)
+          reader_names, writer_names = accessor_names(class_node)
+
+          accessor_macroses(class_node).each do |macro|
+            check(macro, reader_names, writer_names)
+          end
+        end
+        alias on_module on_class
+
+        def autocorrect(node)
+          macro = node.parent
+
+          lambda do |corrector|
+            corrector.replace(macro, replacement(macro, node))
+          end
+        end
+
+        private
+
+        def accessor_names(class_node)
+          reader_names = Set.new
+          writer_names = Set.new
+
+          accessor_macroses(class_node).each do |macro|
+            names = macro.arguments.map(&:value)
+
+            names.each do |name|
+              if attr_reader?(macro)
+                reader_names.add(name)
+              else
+                writer_names.add(name)
+              end
+            end
+          end
+
+          [reader_names, writer_names]
+        end
+
+        def accessor_macroses(class_node)
+          class_def = class_node.body
+          return [] if !class_def || class_def.def_type?
+
+          send_nodes =
+            if class_def.send_type?
+              [class_def]
+            else
+              class_def.each_child_node(:send)
+            end
+
+          send_nodes.select { |node| node.macro? && (attr_reader?(node) || attr_writer?(node)) }
+        end
+
+        def attr_reader?(send_node)
+          send_node.method?(:attr_reader) || send_node.method?(:attr)
+        end
+
+        def attr_writer?(send_node)
+          send_node.method?(:attr_writer)
+        end
+
+        def check(macro, reader_names, writer_names)
+          macro.arguments.each do |arg_node|
+            name = arg_node.value
+
+            if (attr_reader?(macro) && writer_names.include?(name)) ||
+               (attr_writer?(macro) && reader_names.include?(name))
+              add_offense(arg_node, message: format(MSG, name: name))
+            end
+          end
+        end
+
+        def replacement(macro, node)
+          rest_args = macro.arguments
+          rest_args.delete(node)
+          args = rest_args.map(&:source).join(', ')
+
+          if attr_reader?(macro)
+            if args.empty?
+              "attr_accessor #{node.source}"
+            else
+              "attr_accessor #{node.source}\n#{indent(macro)}#{macro.method_name} #{args}"
+            end
+          elsif args.empty?
+            ''
+          else
+            "#{indent(macro)}#{macro.method_name} #{args}"
+          end
+        end
+
+        def indent(node)
+          ' ' * node.loc.column
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/style/bisected_attr_accessor_spec.rb

@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Style::BisectedAttrAccessor do
+  subject(:cop) { described_class.new }
+
+  it 'registers an offense and corrects when both accessors of the name exists' do
+    expect_offense(<<~RUBY)
+      class Foo
+        attr_reader :bar
+                    ^^^^ Combine both accessors into `attr_accessor :bar`.
+        attr_writer :bar
+                    ^^^^ Combine both accessors into `attr_accessor :bar`.
+        other_macro :something
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      class Foo
+        attr_accessor :bar
+
+        other_macro :something
+      end
+    RUBY
+  end
+
+  it 'registers an offense and corrects when attr and attr_writer exists' do
+    expect_offense(<<~RUBY)
+      class Foo
+        attr :bar
+             ^^^^ Combine both accessors into `attr_accessor :bar`.
+        attr_writer :bar
+                    ^^^^ Combine both accessors into `attr_accessor :bar`.
+        other_macro :something
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      class Foo
+        attr_accessor :bar
+
+        other_macro :something
+      end
+    RUBY
+  end
+
+  it 'registers an offense and corrects when both accessors of the name exists and accessor contains multiple names' do
+    expect_offense(<<~RUBY)
+      class Foo
+        attr_reader :baz, :bar, :quux
+                          ^^^^ Combine both accessors into `attr_accessor :bar`.
+        attr_writer :bar
+                    ^^^^ Combine both accessors into `attr_accessor :bar`.
+        other_macro :something
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      class Foo
+        attr_accessor :bar
+        attr_reader :baz, :quux
+
+        other_macro :something
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when only one accessor of the name exists' do
+    expect_no_offenses(<<~RUBY)
+      class Foo
+        attr_reader :bar
+        attr_writer :baz
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `attr_accessor`' do
+    expect_no_offenses(<<~RUBY)
+      class Foo
+        attr_accessor :bar
+      end
+    RUBY
+  end
+end