[Fix rubocop#833] Fix a false positive for Rails/Pluck

Fixes rubocop#833 and rubocop#835.

This commit fixes a false positive for `Rails/Pluck` when using multiple block arguments

Author: koic

changelog/fix_false_positive_for_rails_pluck.md

@@ -0,0 +1 @@
+* [#833](https://github.com/rubocop/rubocop-rails/issues/833): Fix a false positive for `Rails/Pluck` when using multiple block arguments. ([@koic][])

lib/rubocop/cop/rails/pluck.rb

@@ -31,6 +31,8 @@ class Pluck < Base
 
         def on_block(node)
           pluck_candidate?(node) do |argument, key|
+            next unless use_one_block_argument?(argument)
+
             match = if node.block_type?
                       block_argument = argument.children.first.source
                       use_block_argument_in_key?(block_argument, key)
@@ -39,18 +41,19 @@ def on_block(node)
                     end
             next unless match
 
-            replacement = "pluck(#{key.source})"
-            message = message(replacement, node)
-
-            add_offense(offense_range(node), message: message) do |corrector|
-              corrector.replace(offense_range(node), replacement)
-            end
+            register_offense(node, key)
           end
         end
         alias on_numblock on_block
 
         private
 
+        def use_one_block_argument?(argument)
+          return true if argument == 1 # Checks for numbered argument `_1`.
+
+          argument.respond_to?(:one?) && argument.one?
+        end
+
         def use_block_argument_in_key?(block_argument, key)
           key.each_descendant(:lvar).none? { |lvar| block_argument == lvar.source }
         end
@@ -59,6 +62,15 @@ def offense_range(node)
           node.send_node.loc.selector.join(node.loc.end)
         end
 
+        def register_offense(node, key)
+          replacement = "pluck(#{key.source})"
+          message = message(replacement, node)
+
+          add_offense(offense_range(node), message: message) do |corrector|
+            corrector.replace(offense_range(node), replacement)
+          end
+        end
+
         def message(replacement, node)
           current = offense_range(node).source
 

spec/rubocop/cop/rails/pluck_spec.rb

@@ -58,6 +58,14 @@
         end
       end
 
+      context 'when there are multiple block arguments' do
+        it 'does not register an offense' do
+          expect_no_offenses(<<~RUBY)
+            x.#{method} { |_, obj| obj['id'] }
+          RUBY
+        end
+      end
+
       context 'when using Ruby 2.7 or newer', :ruby27 do
         context 'when using numbered parameter' do
           context "when `#{method}` can be replaced with `pluck`" do
@@ -80,6 +88,14 @@
               RUBY
             end
           end
+
+          context 'when numblock argument is not `_1`' do
+            it 'does not register an offense' do
+              expect_no_offenses(<<~RUBY)
+                x.#{method} { _2['id'] }
+              RUBY
+            end
+          end
         end
       end
     end