Ignore unused block parameter if it is a keyword argument

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Bug fixes
 
 * [#2983](https://github.com/bbatsov/rubocop/pull/2983): `Style/AlignParameters` message was clarified for `with_fixed_indentation` style. ([@dylanahsmith][])
+* [#2314](https://github.com/bbatsov/rubocop/pull/2314): Ignore `UnusedBlockArgument` for keyword arguments. ([@volkert][])
 
 ## 0.39.0 (27/03/2016)
 

config/default.yml

@@ -1051,6 +1051,10 @@ Lint/UnusedMethodArgument:
   AllowUnusedKeywordArguments: false
   IgnoreEmptyMethods: true
 
+# Checks for unused block arguments.
+Lint/UnusedBlockArgument:
+  AllowUnusedKeywordArguments: false
+
 ##################### Performance ############################
 
 Performance/RedundantMerge:

lib/rubocop/cop/lint/unused_block_argument.rb

@@ -16,6 +16,8 @@ class UnusedBlockArgument < Cop
 
         def check_argument(variable)
           return unless variable.block_argument?
+          return if variable.keyword_argument? &&
+                    cop_config && cop_config['AllowUnusedKeywordArguments']
 
           if cop_config['IgnoreEmptyBlocks']
             _send, _args, body = *variable.scope.node

spec/rubocop/cli_spec.rb

@@ -147,6 +147,8 @@ def interrupt
                                    '    super(arg1, arg2) { |response| }',
                                    '  end',
                                    'end'])
+        create_file('.rubocop.yml', ['Lint/UnusedBlockArgument:',
+                                     '  IgnoreEmptyBlocks: true'])
         expect(cli.run(['--format', 'simple', 'example.rb'])).to eq(0)
         expect($stdout.string)
           .to eq(['',

spec/rubocop/cop/cop_spec.rb

@@ -95,7 +95,7 @@
       context 'when offense was corrected' do
         before do
           allow(@cop).to receive(:autocorrect?).and_return(true)
-          allow(@cop).to receive(:autocorrect).and_return(->(corrector) {})
+          allow(@cop).to receive(:autocorrect).and_return(->(_corrector) {})
         end
 
         it 'is set to true' do

spec/rubocop/cop/lint/unused_block_argument_spec.rb

@@ -4,7 +4,8 @@
 require 'spec_helper'
 
 describe RuboCop::Cop::Lint::UnusedBlockArgument, :config do
-  subject(:cop) { described_class.new }
+  subject(:cop) { described_class.new(config) }
+  let(:cop_config) { { 'AllowUnusedKeywordArguments' => false } }
 
   context 'inspection' do
     before do
@@ -144,6 +145,31 @@
       end
     end
 
+    context 'when an optional keyword argument is unused', ruby: 2 do
+      let(:source) { <<-END }
+        define_method(:foo) do |bar: 'default'|
+          puts 'bar'
+        end
+      END
+
+      it 'registers an offense but does not suggest underscore-prefix' do
+        expect(cop.offenses.size).to eq(1)
+        expect(cop.highlights).to eq(['bar'])
+        expect(cop.offenses.first.message).to eq(
+          'Unused block argument - `bar`. ' \
+          "You can omit the argument if you don't care about it."
+        )
+      end
+
+      context 'and AllowUnusedKeywordArguments set' do
+        let(:cop_config) { { 'AllowUnusedKeywordArguments' => true } }
+
+        it 'does not care' do
+          expect(cop.offenses).to be_empty
+        end
+      end
+    end
+
     context 'when a method argument is not used' do
       let(:source) { <<-END }
         def some_method(foo)