Add AllowGemfileRubyComment option to Layout/LeadingCommentSpace

This PR remove the offense for comments that starts with `#ruby` as this style is
a valid syntax to write Ruby versions in Gemfile that can be used with bundler, RVM, and others.

Example:

```ruby
  # Specific version (comment) will be used by RVM
  #ruby=2.7.0
  #ruby-gemset=myproject
  ruby '~> 2.7.0'
```

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#7577](https://github.com/rubocop-hq/rubocop/pull/7577): Add `AllowGemfileRubyComment` configuration on `Layout/LeadingCommentSpace`. ([@cetinajero][])
+
 ### Changes
 
 * [#7636](https://github.com/rubocop-hq/rubocop/issues/7636): Remove `console` from `Lint/Debugger` to prevent false positives. ([@gsamokovarov][])
@@ -4324,3 +4328,4 @@
 [@mangara]: https://github.com/mangara
 [@pirj]: https://github.com/pirj
 [@pawptart]: https://github.com/pawptart
+[@cetinajero]: https://github.com/cetinajero

config/default.yml

@@ -794,6 +794,7 @@ Layout/LeadingCommentSpace:
   VersionAdded: '0.49'
   VersionChanged: '0.73'
   AllowDoxygenCommentStyle: false
+  AllowGemfileRubyComment: false
 
 Layout/LeadingEmptyLines:
   Description: Check for unnecessary blank lines at the beginning of a file.

lib/rubocop/cop/layout/leading_comment_space.rb

@@ -35,6 +35,20 @@ module Layout
       #   # Another line of comment
       #   #*
       #
+      # @example AllowGemfileRubyComment: false (default)
+      #
+      #   # bad
+      #
+      #   #ruby=2.7.0
+      #   #ruby-gemset=myproject
+      #
+      # @example AllowGemfileRubyComment: true
+      #
+      #   # good
+      #
+      #   #ruby=2.7.0
+      #   #ruby-gemset=myproject
+      #
       class LeadingCommentSpace < Cop
         include RangeHelp
 
@@ -44,7 +58,8 @@ def investigate(processed_source)
           processed_source.each_comment do |comment|
             next unless comment.text =~ /\A#+[^#\s=:+-]/
             next if comment.loc.line == 1 && allowed_on_first_line?(comment)
-            next if allow_doxygen_comment? && doxygen_comment_style?(comment)
+            next if doxygen_comment_style?(comment)
+            next if gemfile_ruby_comment?(comment)
 
             add_offense(comment)
           end
@@ -80,7 +95,23 @@ def allow_doxygen_comment?
         end
 
         def doxygen_comment_style?(comment)
-          comment.text.start_with?('#*')
+          allow_doxygen_comment? && comment.text.start_with?('#*')
+        end
+
+        def allow_gemfile_ruby_comment?
+          cop_config['AllowGemfileRubyComment']
+        end
+
+        def gemfile?
+          File.basename(processed_source.file_path).eql?('Gemfile')
+        end
+
+        def ruby_comment_in_gemfile?(comment)
+          gemfile? && comment.text.start_with?('#ruby')
+        end
+
+        def gemfile_ruby_comment?(comment)
+          allow_gemfile_ruby_comment? && ruby_comment_in_gemfile?(comment)
         end
       end
     end

manual/cops_layout.md

@@ -2822,12 +2822,29 @@ or rackup options.
 # Another line of comment
 #*
 ```
+#### AllowGemfileRubyComment: false (default)
+
+```ruby
+# bad
+
+#ruby=2.7.0
+#ruby-gemset=myproject
+```
+#### AllowGemfileRubyComment: true
+
+```ruby
+# good
+
+#ruby=2.7.0
+#ruby-gemset=myproject
+```
 
 ### Configurable attributes
 
 Name | Default value | Configurable values
 --- | --- | ---
 AllowDoxygenCommentStyle | `false` | Boolean
+AllowGemfileRubyComment | `false` | Boolean
 
 ### References
 

spec/rubocop/cop/layout/leading_comment_space_spec.rb

@@ -130,4 +130,49 @@
       =end
     RUBY
   end
+
+  describe 'Gemfile Ruby comment' do
+    context 'when config option is disabled' do
+      let(:cop_config) { { 'AllowGemfileRubyComment' => false } }
+
+      it 'registers an offense when using ruby config as comment' do
+        expect_offense(<<~'RUBY')
+          # Specific version (comment) will be used by RVM
+          #ruby=2.7.0
+          ^^^^^^^^^^^ Missing space after `#`.
+          #ruby-gemset=myproject
+          ^^^^^^^^^^^^^^^^^^^^^^ Missing space after `#`.
+          ruby '~> 2.7.0'
+        RUBY
+      end
+    end
+
+    context 'when config option is enabled' do
+      let(:cop_config) { { 'AllowGemfileRubyComment' => true } }
+
+      context 'file not named Gemfile' do
+        it 'registers an offense when using ruby config as comment' do
+          expect_offense(<<~'RUBY', 'test/test_case.rb')
+            # Specific version (comment) will be used by RVM
+            #ruby=2.7.0
+            ^^^^^^^^^^^ Missing space after `#`.
+            #ruby-gemset=myproject
+            ^^^^^^^^^^^^^^^^^^^^^^ Missing space after `#`.
+            ruby '~> 2.7.0'
+          RUBY
+        end
+      end
+
+      context 'file named Gemfile' do
+        it 'does not register an offense when using ruby config as comment' do
+          expect_no_offenses(<<~'RUBY', 'Gemfile')
+            # Specific version (comment) will be used by RVM
+            #ruby=2.7.0
+            #ruby-gemset=myproject
+            ruby '~> 2.7.0'
+          RUBY
+        end
+      end
+    end
+  end
 end