Add AllowKeywordBlockArguments option to UnderscorePrefixedVariableName

CHANGELOG.md

@@ -29,6 +29,7 @@
 * [#6903](https://github.com/rubocop-hq/rubocop/issues/6903): Handle variables prefixed with `_` in `Naming/RescuedExceptionsVariableName` cop. ([@anthony-robin][])
 * [#6917](https://github.com/rubocop-hq/rubocop/issues/6917): Bump Bundler dependency to >= 1.15.0. ([@koic][])
 * Add `--auto-gen-only-exclude` to the command outputted in `rubocop_todo.yml` if the option is specified. ([@dvandersluis][])
+* [#6887](https://github.com/rubocop-hq/rubocop/pull/6887): Allow `Lint/UnderscorePrefixedVariableName` cop to be configured to allow use of block keyword args. ([@dduugg][])
 
 ## 0.67.2 (2019-04-05)
 

config/default.yml

@@ -1564,6 +1564,7 @@ Lint/UnderscorePrefixedVariableName:
   Description: 'Do not use prefix `_` for a variable that is used.'
   Enabled: true
   VersionAdded: '0.21'
+  AllowKeywordBlockArguments: false
 
 Lint/UnifiedInteger:
   Description: 'Use Integer instead of Fixnum or Bignum'

lib/rubocop/cop/lint/underscore_prefixed_variable_name.rb

@@ -6,29 +6,40 @@ module Lint
       # This cop checks for underscore-prefixed variables that are actually
       # used.
       #
-      # @example
+      # Since block keyword arguments cannot be arbitrarily named at call
+      # sites, the `AllowKeywordBlockArguments` will allow use of underscore-
+      # prefixed block keyword arguments.
+      #
+      # @example AllowKeywordBlockArguments: false (default)
       #
       #   # bad
       #
       #   [1, 2, 3].each do |_num|
       #     do_something(_num)
       #   end
       #
-      # @example
+      #   query(:sales) do |_id:, revenue:, cost:|
+      #     {_id: _id, profit: revenue - cost}
+      #   end
       #
       #   # good
       #
       #   [1, 2, 3].each do |num|
       #     do_something(num)
       #   end
       #
-      # @example
+      #   [1, 2, 3].each do |_num|
+      #     do_something # not using `_num`
+      #   end
+      #
+      # @example AllowKeywordBlockArguments: true
       #
       #   # good
       #
-      #   [1, 2, 3].each do |_num|
-      #     do_something # not using `_num`
+      #   query(:sales) do |_id:, revenue:, cost:|
+      #     {_id: _id, profit: revenue - cost}
       #   end
+      #
       class UnderscorePrefixedVariableName < Cop
         MSG = 'Do not use prefix `_` for a variable that is used.'.freeze
 
@@ -45,6 +56,7 @@ def after_leaving_scope(scope, _variable_table)
         def check_variable(variable)
           return unless variable.should_be_unused?
           return if variable.references.none?(&:explicit?)
+          return if allowed_keyword_block_argument?(variable)
 
           node = variable.declaration_node
 
@@ -56,6 +68,14 @@ def check_variable(variable)
 
           add_offense(nil, location: location)
         end
+
+        private
+
+        def allowed_keyword_block_argument?(variable)
+          variable.block_argument? &&
+            variable.keyword_argument? &&
+            cop_config['AllowKeywordBlockArguments']
+        end
       end
     end
   end

manual/cops_lint.md

@@ -2077,30 +2077,51 @@ Enabled | Yes | No | 0.21 | -
 This cop checks for underscore-prefixed variables that are actually
 used.
 
+Since block keyword arguments cannot be arbitrarily named at call
+sites, the `AllowKeywordBlockArguments` will allow use of underscore-
+prefixed block keyword arguments.
+
 ### Examples
 
+#### AllowKeywordBlockArguments: false (default)
+
 ```ruby
 # bad
 
 [1, 2, 3].each do |_num|
   do_something(_num)
 end
-```
-```ruby
+
+query(:sales) do |_id:, revenue:, cost:|
+  {_id: _id, profit: revenue - cost}
+end
+
 # good
 
 [1, 2, 3].each do |num|
   do_something(num)
 end
+
+[1, 2, 3].each do |_num|
+  do_something # not using `_num`
+end
 ```
+#### AllowKeywordBlockArguments: true
+
 ```ruby
 # good
 
-[1, 2, 3].each do |_num|
-  do_something # not using `_num`
+query(:sales) do |_id:, revenue:, cost:|
+  {_id: _id, profit: revenue - cost}
 end
 ```
 
+### Configurable attributes
+
+Name | Default value | Configurable values
+--- | --- | ---
+AllowKeywordBlockArguments | `false` | Boolean
+
 ## Lint/UnifiedInteger
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged

spec/rubocop/cop/lint/underscore_prefixed_variable_name_spec.rb

@@ -1,7 +1,9 @@
 # frozen_string_literal: true
 
-RSpec.describe RuboCop::Cop::Lint::UnderscorePrefixedVariableName do
-  subject(:cop) { described_class.new }
+RSpec.describe RuboCop::Cop::Lint::UnderscorePrefixedVariableName, :config do
+  subject(:cop) { described_class.new(config) }
+
+  let(:cop_config) { { 'AllowKeywordBlockArguments' => false } }
 
   context 'when an underscore-prefixed variable is used' do
     it 'registers an offense' do
@@ -49,14 +51,41 @@ def some_method(_foo)
   end
 
   context 'when an underscore-prefixed block argument is used' do
+    [true, false].each do |config|
+      let(:cop_config) { { 'AllowKeywordBlockArguments' => config } }
+
+      it 'registers an offense' do
+        expect_offense(<<-RUBY.strip_indent)
+          1.times do |_foo|
+                      ^^^^ Do not use prefix `_` for a variable that is used.
+            puts _foo
+          end
+        RUBY
+      end
+    end
+  end
+
+  context 'when an underscore-prefixed keyword block argument is used' do
     it 'registers an offense' do
       expect_offense(<<-RUBY.strip_indent)
-        1.times do |_foo|
-                    ^^^^ Do not use prefix `_` for a variable that is used.
+        define_method(:foo) do |_foo: 'default'|
+                                ^^^^ Do not use prefix `_` for a variable that is used.
           puts _foo
         end
       RUBY
     end
+
+    context 'when AllowKeywordBlockArguments is set' do
+      let(:cop_config) { { 'AllowKeywordBlockArguments' => true } }
+
+      it 'does not register an offense' do
+        expect_no_offenses(<<-RUBY.strip_indent)
+          define_method(:foo) do |_foo: 'default'|
+            puts _foo
+          end
+        RUBY
+      end
+    end
   end
 
   context 'when an underscore-prefixed variable in top-level scope is used' do