Add new Lint/ItWithoutArgumentsInBlock cop

changelog/new_add_new_lint_it_without_arguments_in_block_cop.md

@@ -0,0 +1 @@
+* [#12516](https://github.com/rubocop/rubocop/pull/12516): Add new `Lint/ItWithoutArgumentsInBlock` cop. ([@koic][])

config/default.yml

@@ -1963,6 +1963,12 @@ Lint/InterpolationCheck:
   VersionAdded: '0.50'
   VersionChanged: '1.40'
 
+Lint/ItWithoutArgumentsInBlock:
+  Description: 'Checks uses of `it` calls without arguments in block.'
+  Reference: 'https://bugs.ruby-lang.org/issues/18980'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Lint/LambdaWithoutLiteralBlock:
   Description: 'Checks uses of lambda without a literal block.'
   Enabled: pending

lib/rubocop.rb

@@ -332,6 +332,7 @@
 require_relative 'rubocop/cop/lint/ineffective_access_modifier'
 require_relative 'rubocop/cop/lint/inherit_exception'
 require_relative 'rubocop/cop/lint/interpolation_check'
+require_relative 'rubocop/cop/lint/it_without_arguments_in_block'
 require_relative 'rubocop/cop/lint/lambda_without_literal_block'
 require_relative 'rubocop/cop/lint/literal_as_condition'
 require_relative 'rubocop/cop/lint/literal_assignment_in_condition'

lib/rubocop/cop/lint/it_without_arguments_in_block.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # Emulates the following Ruby warning in Ruby 3.3.
+      #
+      # [source,ruby]
+      # ----
+      # $ ruby -e '0.times { it }'
+      # -e:1: warning: `it` calls without arguments will refer to the first block param in Ruby 3.4;
+      # use it() or self.it
+      # ----
+      #
+      # `it` calls without arguments will refer to the first block param in Ruby 3.4.
+      # So use `it()` or `self.it` to ensure compatibility.
+      #
+      # @example
+      #
+      #   # bad
+      #   do_something { it }
+      #
+      #   # good
+      #   do_something { it() }
+      #   do_something { self.it }
+      #
+      class ItWithoutArgumentsInBlock < Base
+        include NodePattern::Macros
+
+        MSG = '`it` calls without arguments will refer to the first block param in Ruby 3.4; ' \
+              'use `it()` or `self.it`.'
+
+        def on_block(node) # rubocop:disable InternalAffairs/NumblockHandler
+          return unless (body = node.body)
+          return unless node.arguments.empty_and_without_delimiters?
+
+          if body.send_type? && deprecated_it_method?(body)
+            add_offense(body)
+          else
+            body.each_descendant(:send).each do |send_node|
+              next unless deprecated_it_method?(send_node)
+
+              add_offense(send_node)
+            end
+          end
+        end
+
+        def deprecated_it_method?(node)
+          return false unless node.method?(:it)
+
+          !node.receiver && node.arguments.empty? && !node.parenthesized? && !node.block_literal?
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/it_without_arguments_in_block_spec.rb

@@ -0,0 +1,139 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::ItWithoutArgumentsInBlock, :config do
+  it 'registers an offense when using `it` without arguments in the single line block' do
+    expect_offense(<<~RUBY)
+      0.times { it }
+                ^^ `it` calls without arguments will refer to the first block param in Ruby 3.4; use `it()` or `self.it`.
+    RUBY
+  end
+
+  it 'registers an offense when using `it` without arguments in the multiline block' do
+    expect_offense(<<~RUBY)
+      0.times do
+        it
+        ^^ `it` calls without arguments will refer to the first block param in Ruby 3.4; use `it()` or `self.it`.
+        it = 1
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` with arguments in the single line block' do
+    expect_no_offenses(<<~RUBY)
+      0.times { it(42) }
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` with block argument in the single line block' do
+    expect_no_offenses(<<~RUBY)
+      0.times { it { do_something } }
+    RUBY
+  end
+
+  it 'does not register an offense when using `it()` in the single line block' do
+    expect_no_offenses(<<~RUBY)
+      0.times { it() }
+    RUBY
+  end
+
+  it 'does not register an offense when using `self.it` in the single line block' do
+    expect_no_offenses(<<~RUBY)
+      0.times { self.it }
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` with arguments in the multiline block' do
+    expect_no_offenses(<<~RUBY)
+      0.times do
+        it(42)
+        it = 1
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` with block argument in the multiline block' do
+    expect_no_offenses(<<~RUBY)
+      0.times do
+        it { do_something }
+        it = 1
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it()` in the multiline block' do
+    expect_no_offenses(<<~RUBY)
+      0.times do
+        it()
+        it = 1
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `self.it` without arguments in the multiline block' do
+    expect_no_offenses(<<~RUBY)
+      0.times do
+        self.it
+        it = 1
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` without arguments in `if` body' do
+    expect_no_offenses(<<~RUBY)
+      if false
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` without arguments in `def` body' do
+    expect_no_offenses(<<~RUBY)
+      def foo
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` without arguments in the block with empty block parameter' do
+    expect_no_offenses(<<~RUBY)
+      0.times { ||
+        it
+      }
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` without arguments in the block with useless block parameter' do
+    expect_no_offenses(<<~RUBY)
+      0.times { |_n|
+        it
+      }
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` inner local variable in block' do
+    expect_no_offenses(<<~RUBY)
+      0.times do
+        it = 1
+        it
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when using `it` outer local variable in block' do
+    expect_no_offenses(<<~RUBY)
+      it = 1
+      0.times { it }
+    RUBY
+  end
+
+  it 'does not register an offense when using empty block' do
+    expect_no_offenses(<<~RUBY)
+      0.times {}
+    RUBY
+  end
+end