Support AllowComments option for Style/EmptyElse

This PR is support `AllowComments` option for `Style/EmptyElse`.
The default for this option is false.

In the case of complex conditional statements,
we may want to leave `else` empty or nil and
write only the explanation of the `else` case in the comments.

`AllowComments: true` will not treat when `else` as offense
if the `else` with an intentional comment.

### @example AllowComments: false (default)

```ruby
# bad
if condition
  statement
else
  # something comment
  nil
end

# bad
if condition
  statement
else
  # something comment
end
```

### @example AllowComments: true

```ruby
# good
if condition
  statement
else
  # something comment
  nil
end

# good
if condition
  statement
else
  # something comment
end
```

changelog/new_support_allow_comments_for_empty_else.md

@@ -0,0 +1 @@
+* [#10790](https://github.com/rubocop/rubocop/pull/10790): Support `AllowComments` option for `Style/EmptyElse`. ([@ydah][])

config/default.yml

@@ -3512,6 +3512,7 @@ Style/EmptyElse:
     - empty
     - nil
     - both
+  AllowComments: false
 
 Style/EmptyLambdaParameter:
   Description: 'Omit parens for empty lambda parameters.'

lib/rubocop/cop/style/empty_else.rb

@@ -89,6 +89,41 @@ module Style
       #   if condition
       #     statement
       #   end
+      #
+      # @example AllowComments: false (default)
+      #
+      #   # bad
+      #   if condition
+      #     statement
+      #   else
+      #     # something comment
+      #     nil
+      #   end
+      #
+      #   # bad
+      #   if condition
+      #     statement
+      #   else
+      #     # something comment
+      #   end
+      #
+      # @example AllowComments: true
+      #
+      #   # good
+      #   if condition
+      #     statement
+      #   else
+      #     # something comment
+      #     nil
+      #   end
+      #
+      #   # good
+      #   if condition
+      #     statement
+      #   else
+      #     # something comment
+      #   end
+      #
       class EmptyElse < Base
         include OnNormalIfUnless
         include ConfigurableEnforcedStyle
@@ -108,6 +143,8 @@ def on_case(node)
         private
 
         def check(node)
+          return if cop_config['AllowComments'] && comment_in_else?(node.loc)
+
           empty_check(node) if empty_style?
           nil_check(node) if nil_style?
         end

spec/rubocop/cop/style/empty_else_spec.rb

@@ -530,6 +530,174 @@
     end
   end
 
+  context 'when `AllowComments: true`' do
+    let(:config) do
+      RuboCop::Config.new('Style/EmptyElse' => {
+                            'AllowComments' => true,
+                            'EnforcedStyle' => 'both',
+                            'SupportedStyles' => %w[empty nil both]
+                          },
+                          'Style/MissingElse' => missing_else_config)
+    end
+
+    context 'given an if-statement' do
+      context 'with not comment and empty else-clause' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY)
+            if condition
+              statement
+            else
+            ^^^^ Redundant `else`-clause.
+            end
+          RUBY
+        end
+      end
+
+      context 'with not comment and nil else-clause' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY)
+            if condition
+              statement
+            else
+            ^^^^ Redundant `else`-clause.
+              nil
+            end
+          RUBY
+        end
+      end
+
+      context 'with comment and empty else-clause' do
+        it "doesn't register an offense" do
+          expect_no_offenses(<<~RUBY)
+            if condition
+              statement
+            else
+              # some comment
+            end
+          RUBY
+        end
+      end
+
+      context 'with comment and nil else-clause' do
+        it "doesn't register an offense" do
+          expect_no_offenses(<<~RUBY)
+            if condition
+              statement
+            else
+              nil # some comment
+            end
+          RUBY
+        end
+      end
+    end
+
+    context 'given an unless-statement' do
+      context 'with not comment and empty else-clause' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY)
+            unless condition
+              statement
+            else
+            ^^^^ Redundant `else`-clause.
+            end
+          RUBY
+        end
+      end
+
+      context 'with not comment and nil else-clause' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY)
+            unless condition
+              statement
+            else
+            ^^^^ Redundant `else`-clause.
+              nil
+            end
+          RUBY
+        end
+      end
+
+      context 'with comment and empty else-clause' do
+        it "doesn't register an offense" do
+          expect_no_offenses(<<~RUBY)
+            unless condition
+              statement
+            else
+              # some comment
+            end
+          RUBY
+        end
+      end
+
+      context 'with comment and nil else-clause' do
+        it "doesn't register an offense" do
+          expect_no_offenses(<<~RUBY)
+            unless condition
+              statement
+            else
+              nil # some comment
+            end
+          RUBY
+        end
+      end
+    end
+
+    context 'given a case statement' do
+      context 'with not comment and empty else-clause' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY)
+            case a
+            when condition
+              statement
+            else
+            ^^^^ Redundant `else`-clause.
+            end
+          RUBY
+        end
+      end
+
+      context 'with not comment and nil else-clause' do
+        it 'registers an offense' do
+          expect_offense(<<~RUBY)
+            case a
+            when condition
+              statement
+            else
+            ^^^^ Redundant `else`-clause.
+              nil
+            end
+          RUBY
+        end
+      end
+
+      context 'with comment and empty else-clause' do
+        it "doesn't register an offense" do
+          expect_no_offenses(<<~RUBY)
+            case a
+            when condition
+              statement
+            else
+              # some comment
+            end
+          RUBY
+        end
+      end
+
+      context 'with comment and nil else-clause' do
+        it "doesn't register an offense" do
+          expect_no_offenses(<<~RUBY)
+            case a
+            when condition
+              statement
+            else
+              nil # some comment
+            end
+          RUBY
+        end
+      end
+    end
+  end
+
   context 'with nested if and case statement' do
     let(:config) do
       RuboCop::Config.new('Style/EmptyElse' => {