Support Ruby 2.7's numbered parameter for Style/RedundantSort

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#7654](https://github.com/rubocop-hq/rubocop/issues/7654): Support `with_fixed_indentation` option for `Layout/ArrayAlignment` cop. ([@nikitasakov][])
+* [#7783](https://github.com/rubocop-hq/rubocop/pull/7783): Support Ruby 2.7's numbered parameter for `Style/RedundantSort`. ([@koic][])
 
 ### Bug fixes
 

lib/rubocop/cop/style/redundant_sort.rb

@@ -63,9 +63,9 @@ class RedundantSort < Cop
             (send $(send _ $:sort_by _) ${:last :first})
             (send $(send _ $:sort_by _) ${:[] :at :slice} {(int 0) (int -1)})
 
-            (send (block $(send _ ${:sort_by :sort}) ...) ${:last :first})
+            (send ({block numblock} $(send _ ${:sort_by :sort}) ...) ${:last :first})
             (send
-              (block $(send _ ${:sort_by :sort}) ...)
+              ({block numblock} $(send _ ${:sort_by :sort}) ...)
               ${:[] :at :slice} {(int 0) (int -1)}
             )
           }

spec/rubocop/cop/style/redundant_sort_spec.rb

@@ -178,4 +178,42 @@
       expect(new_source).to eq('foo.max_by { |x| x.something }')
     end
   end
+
+  context '>= Ruby 2.7', :ruby27 do
+    context 'when using numbered parameter' do
+      it 'registers an offense and corrects when last is called on sort with ' \
+         'comparator' do
+        expect_offense(<<~RUBY)
+          foo.sort { _2 <=> _1 }.last
+              ^^^^^^^^^^^^^^^^^^^^^^^ Use `max` instead of `sort...last`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          foo.max { _2 <=> _1 }
+        RUBY
+      end
+
+      it 'registers an offense and corrects when first is called on sort_by' do
+        expect_offense(<<~RUBY)
+          [1, 2, 3].sort_by { _1.length }.first
+                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `min_by` instead of `sort_by...first`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          [1, 2, 3].min_by { _1.length }
+        RUBY
+      end
+
+      it 'registers an offense and corrects when at(0) is called on sort_by' do
+        expect_offense(<<~RUBY)
+          [1, 2, 3].sort_by { _1.foo }.at(0)
+                    ^^^^^^^^^^^^^^^^^^^^^^^^ Use `min_by` instead of `sort_by...at(0)`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          [1, 2, 3].min_by { _1.foo }
+        RUBY
+      end
+    end
+  end
 end