Add new Lint/DeprecatedConstants cop

changelog/new_add_new_deprecated_constants_cop.md

@@ -0,0 +1 @@
+* [#9324](https://github.com/rubocop-hq/rubocop/pull/9324): Add new `Lint/DeprecatedConstants` cop. ([@koic][])

config/default.yml

@@ -1469,6 +1469,34 @@ Lint/DeprecatedClassMethods:
   Enabled: true
   VersionAdded: '0.19'
 
+Lint/DeprecatedConstants:
+  Description: 'Checks for deprecated constants.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+  # You can configure deprecated constants.
+  # If there is an alternative method, you can set alternative value as `Alternative`.
+  # And you can set the deprecated version as `DeprecatedVersion`.
+  # These options can be omitted if they are not needed.
+  #
+  # DeprecatedConstants:
+  #   'DEPRECATED_CONSTANT':
+  #     Alternative: 'alternative_value'
+  #     DeprecatedVersion: 'deprecated_version'
+  #
+  DeprecatedConstants:
+    'NIL':
+      Alternative: 'nil'
+      DeprecatedVersion: '2.4'
+    'TRUE':
+      Alternative: 'true'
+      DeprecatedVersion: '2.4'
+    'FALSE':
+      Alternative: 'false'
+      DeprecatedVersion: '2.4'
+    'Random::DEFAULT':
+      Alternative: 'Random.new'
+      DeprecatedVersion: '3.0'
+
 Lint/DeprecatedOpenSSLConstant:
   Description: "Don't use algorithm constants for `OpenSSL::Cipher` and `OpenSSL::Digest`."
   Enabled: true

lib/rubocop.rb

@@ -262,6 +262,7 @@
 require_relative 'rubocop/cop/lint/constant_resolution'
 require_relative 'rubocop/cop/lint/debugger'
 require_relative 'rubocop/cop/lint/deprecated_class_methods'
+require_relative 'rubocop/cop/lint/deprecated_constants'
 require_relative 'rubocop/cop/lint/deprecated_open_ssl_constant'
 require_relative 'rubocop/cop/lint/disjunctive_assignment_in_constructor'
 require_relative 'rubocop/cop/lint/duplicate_branch'

lib/rubocop/cop/lint/deprecated_constants.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for deprecated constants.
+      #
+      # It has `DeprecatedConstants` config. If there is an alternative method, you can set
+      # alternative value as `Alternative`. And you can set the deprecated version as
+      # `DeprecatedVersion`. These options can be omitted if they are not needed.
+      #
+      #   DeprecatedConstants:
+      #     'DEPRECATED_CONSTANT':
+      #       Alternative: 'alternative_value'
+      #       DeprecatedVersion: 'deprecated_version'
+      #
+      # By default, `NIL`, `TRUE`, `FALSE` and `Random::DEFAULT` are configured.
+      #
+      # @example
+      #
+      #   # bad
+      #   NIL
+      #   TRUE
+      #   FALSE
+      #   Random::DEFAULT # Return value of Ruby 2 is `Random` instance, Ruby 3.0 is `Random` class.
+      #
+      #   # good
+      #   nil
+      #   true
+      #   false
+      #   Random.new # `::DEFAULT` has been deprecated in Ruby 3, `.new` is compatible with Ruby 2.
+      #
+      class DeprecatedConstants < Base
+        extend AutoCorrector
+
+        SUGGEST_GOOD_MSG = 'Use `%<good>s` instead of `%<bad>s`%<deprecated_message>s.'
+        DO_NOT_USE_MSG = 'Do not use `%<bad>s`%<deprecated_message>s.'
+
+        def on_const(node)
+          constant = node.absolute? ? consntant_name(node, node.short_name.to_s) : node.source
+          return unless (deprecated_constant = deprecated_constants[constant])
+
+          alternative = deprecated_constant['Alternative']
+          version = deprecated_constant['DeprecatedVersion']
+
+          add_offense(node, message: message(alternative, node.source, version)) do |corrector|
+            corrector.replace(node, alternative)
+          end
+        end
+
+        private
+
+        def consntant_name(node, nested_constant_name)
+          return nested_constant_name unless node.namespace.const_type?
+
+          consntant_name(node.namespace, "#{node.namespace.short_name}::#{nested_constant_name}")
+        end
+
+        def message(good, bad, deprecated_version)
+          deprecated_message = ", deprecated since Ruby #{deprecated_version}" if deprecated_version
+
+          if good
+            format(SUGGEST_GOOD_MSG, good: good, bad: bad, deprecated_message: deprecated_message)
+          else
+            format(DO_NOT_USE_MSG, bad: bad, deprecated_message: deprecated_message)
+          end
+        end
+
+        def deprecated_constants
+          cop_config.fetch('DeprecatedConstants', {})
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/deprecated_constants_spec.rb

@@ -0,0 +1,142 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::DeprecatedConstants, :config do
+  let(:cop_config) do
+    {
+      'DeprecatedConstants' => {
+        'NIL' => { 'Alternative' => 'nil', 'DeprecatedVersion' => '2.4' },
+        'TRUE' => { 'Alternative' => 'true', 'DeprecatedVersion' => '2.4' },
+        'FALSE' => { 'Alternative' => 'false', 'DeprecatedVersion' => '2.4' },
+        'Random::DEFAULT' => { 'Alternative' => 'Random.new', 'DeprecatedVersion' => '3.0' },
+        'Triple::Nested::Constant' => { 'Alternative' => 'Value', 'DeprecatedVersion' => '2.4' },
+        'Have::No::Alternative' => { 'DeprecatedVersion' => '2.4' },
+        'Have::No::DeprecatedVersion' => { 'Alternative' => 'Value' }
+      }
+    }
+  end
+
+  it 'registers and corrects an offense when using `NIL`' do
+    expect_offense(<<~RUBY)
+      NIL
+      ^^^ Use `nil` instead of `NIL`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      nil
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `TRUE`' do
+    expect_offense(<<~RUBY)
+      TRUE
+      ^^^^ Use `true` instead of `TRUE`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      true
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `FALSE`' do
+    expect_offense(<<~RUBY)
+      FALSE
+      ^^^^^ Use `false` instead of `FALSE`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      false
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `Random::DEFAULT`' do
+    expect_offense(<<~RUBY)
+      Random::DEFAULT
+      ^^^^^^^^^^^^^^^ Use `Random.new` instead of `Random::DEFAULT`, deprecated since Ruby 3.0.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Random.new
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::NIL`' do
+    expect_offense(<<~RUBY)
+      ::NIL
+      ^^^^^ Use `nil` instead of `::NIL`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      nil
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::TRUE`' do
+    expect_offense(<<~RUBY)
+      ::TRUE
+      ^^^^^^ Use `true` instead of `::TRUE`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      true
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::FALSE`' do
+    expect_offense(<<~RUBY)
+      ::FALSE
+      ^^^^^^^ Use `false` instead of `::FALSE`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      false
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::Random::DEFAULT`' do
+    expect_offense(<<~RUBY)
+      ::Random::DEFAULT
+      ^^^^^^^^^^^^^^^^^ Use `Random.new` instead of `::Random::DEFAULT`, deprecated since Ruby 3.0.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Random.new
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using `::Triple::Nested::Constant`' do
+    expect_offense(<<~RUBY)
+      ::Triple::Nested::Constant
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `Value` instead of `::Triple::Nested::Constant`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Value
+    RUBY
+  end
+
+  it 'registers and corrects an offense when using deprecated methods that have no alternative' do
+    expect_offense(<<~RUBY)
+      Have::No::Alternative
+      ^^^^^^^^^^^^^^^^^^^^^ Do not use `Have::No::Alternative`, deprecated since Ruby 2.4.
+    RUBY
+
+    expect_no_corrections
+  end
+
+  it 'registers and corrects an offense when using deprecated methods that have no deprecated version' do
+    expect_offense(<<~RUBY)
+      Have::No::DeprecatedVersion
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `Value` instead of `Have::No::DeprecatedVersion`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      Value
+    RUBY
+  end
+
+  it 'does not register an offense when not using deprecated consntant' do
+    expect_no_offenses(<<~RUBY)
+      Foo::TRUE
+    RUBY
+  end
+end