Add new InternalAffairs/CopDescription cop

Enforces the cop discription to start with a word such as verb.

## example

```rb
# bad
# This cop checks ....
class SomeCop < Base
  ....
end

# good
# Checks ...
class SomeCop < Base
  ...
end
```

lib/rubocop/cop/internal_affairs.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require_relative 'internal_affairs/cop_description'
 require_relative 'internal_affairs/empty_line_between_expect_offense_and_correction'
 require_relative 'internal_affairs/example_description'
 require_relative 'internal_affairs/inherit_deprecated_cop_class'

lib/rubocop/cop/internal_affairs/cop_description.rb

@@ -0,0 +1,96 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module InternalAffairs
+      # Enforces the cop description to start with a word such as verb.
+      #
+      # @example
+      #   # bad
+      #   # This cop checks ....
+      #   class SomeCop < Base
+      #     ....
+      #   end
+      #
+      #   # good
+      #   # Checks ...
+      #   class SomeCop < Base
+      #     ...
+      #   end
+      #
+      class CopDescription < Base
+        extend AutoCorrector
+
+        MSG = 'Description should be started with %<suggestion>s instead of `This cop ...`.'
+
+        SPECIAL_WORDS = %w[is can could should will would must may].freeze
+        COP_DESC_OFFENSE_REGEX = \
+          /^\s+# This cop (?<special>#{SPECIAL_WORDS.join('|')})?\s*(?<word>.+?) .*/.freeze
+        REPLACEMENT_REGEX = /^\s+# This cop (#{SPECIAL_WORDS.join('|')})?\s*(.+?) /.freeze
+
+        def on_class(node)
+          return unless (module_node = node.parent)
+
+          description_beginning = first_comment_line(module_node)
+          return unless description_beginning
+
+          start_with_subject = description_beginning.match(COP_DESC_OFFENSE_REGEX)
+          return unless start_with_subject
+
+          suggestion = start_with_subject['word']&.capitalize
+          range = range(module_node, description_beginning)
+          suggestion_for_message = suggestion_for_message(suggestion, start_with_subject)
+          message = format(MSG, suggestion: suggestion_for_message)
+
+          add_offense(range, message: message) do |corrector|
+            if suggestion && !start_with_subject['special']
+              replace_with_suggestion(corrector, range, suggestion, description_beginning)
+            end
+          end
+        end
+
+        private
+
+        def replace_with_suggestion(corrector, range, suggestion, description_beginning)
+          replacement = description_beginning.gsub(REPLACEMENT_REGEX, "#{suggestion} ")
+          corrector.replace(range, replacement)
+        end
+
+        def range(node, comment_line)
+          source_buffer = node.loc.expression.source_buffer
+
+          begin_pos = node.loc.expression.begin_pos
+          begin_pos += comment_index(node, comment_line)
+          end_pos = begin_pos + comment_body(comment_line).length
+
+          Parser::Source::Range.new(source_buffer, begin_pos, end_pos)
+        end
+
+        def suggestion_for_message(suggestion, match_data)
+          if suggestion && !match_data['special']
+            "`#{suggestion}`"
+          else
+            'a word such as verb'
+          end
+        end
+
+        def first_comment_line(node)
+          node.loc.expression.source.lines.find { |line| comment_line?(line) }
+        end
+
+        def comment_body(comment_line)
+          comment_line.gsub(/^\s*# /, '')
+        end
+
+        def comment_index(node, comment_line)
+          body = comment_body(comment_line)
+          node.loc.expression.source.index(body)
+        end
+
+        def relevant_file?(file)
+          file.match?(%r{/cop/.*\.rb\z})
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/internal_affairs/cop_description_spec.rb

@@ -0,0 +1,123 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::InternalAffairs::CopDescription, :config do
+  before do
+    allow_any_instance_of(described_class).to receive(:relevant_file?).and_return(true) # rubocop:disable RSpec/AnyInstance
+  end
+
+  context 'The description starts with `This cop ...`' do
+    it 'registers an offense and corrects if using just a verb' do
+      expect_offense(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              # This cop checks some offenses...
+                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Description should be started with `Checks` instead of `This cop ...`.
+              #
+              # ...
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              # Checks some offenses...
+              #
+              # ...
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+    end
+
+    it 'registers an offense if using an auxiliary verb' do
+      expect_offense(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              # This cop can check some offenses...
+                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Description should be started with a word such as verb instead of `This cop ...`.
+              #
+              # ...
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+    end
+
+    it 'registers an offense if the description like `This cop is ...`' do
+      expect_offense(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              # This cop is used to...
+                ^^^^^^^^^^^^^^^^^^^^^^ Description should be started with a word such as verb instead of `This cop ...`.
+              #
+              # ...
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+    end
+  end
+
+  context 'The description starts with a word such as verb' do
+    it 'does not register if the description like `Checks`' do
+      expect_no_offenses(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              # Checks some problem
+              #
+              # ...
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+    end
+
+    it 'does not register if the description starts with non-verb word' do
+      expect_no_offenses(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              # Either foo or bar ...
+              #
+              # ...
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+    end
+  end
+
+  context 'There is no description comment' do
+    it 'does not register offense' do
+      expect_no_offenses(<<~RUBY)
+        module RuboCop
+          module Cop
+            module Lint
+              class Foo < Base
+              end
+            end
+          end
+        end
+      RUBY
+    end
+  end
+end