[Fix #10061] Fix a false positive for Style/RedundantSort

changelog/fix_a_false_positive_for_style_redundant_sort.md

@@ -0,0 +1 @@
+* [#10061](https://github.com/rubocop/rubocop/issues/10061): Fix a false positive for `Style/RedundantSort` when using `size` method in the block. ([@koic][])

lib/rubocop/cop/style/redundant_sort.rb

@@ -76,22 +76,37 @@ class RedundantSort < Base
 
         def on_send(node)
           if (sort_node, sorter, accessor = redundant_sort?(node.parent))
+            return if use_size_method_in_block?(sort_node)
+
             ancestor = node.parent
           elsif (sort_node, sorter, accessor = redundant_sort?(node.parent&.parent))
+            return if use_size_method_in_block?(sort_node)
+
             ancestor = node.parent.parent
           else
             return
           end
 
+          register_offense(ancestor, sort_node, sorter, accessor)
+        end
+
+        private
+
+        def use_size_method_in_block?(sort_node)
+          return true if sort_node.send_type? && sort_node.block_node&.body&.method?(:size)
+          return false unless sort_node.block_argument?
+
+          sort_node.last_argument.children.first.value == :size
+        end
+
+        def register_offense(ancestor, sort_node, sorter, accessor)
           message = message(ancestor, sorter, accessor)
 
           add_offense(offense_range(sort_node, ancestor), message: message) do |corrector|
             autocorrect(corrector, ancestor, sort_node, sorter, accessor)
           end
         end
 
-        private
-
         def autocorrect(corrector, node, sort_node, sorter, accessor)
           # Remove accessor, e.g. `first` or `[-1]`.
           corrector.remove(range_between(accessor_start(node), node.loc.expression.end_pos))

spec/rubocop/cop/style/redundant_sort_spec.rb

@@ -231,7 +231,17 @@
     expect_no_offenses('[[1, 2], [3, 4]].first.sort')
   end
 
-  # `[2, 1, 3].sort_by.first` is equivalent to `[2, 1, 3].first`, but this
+  # `[3, 1, 2].sort_by(&:size).last` is equivalent to `[3, 1, 2].max_by(&:size)`.
+  it 'does not register an offense when using `sort_by(&:size).last`' do
+    expect_no_offenses('[2, 1, 3].sort_by(&:size).last')
+  end
+
+  # `[3, 1, 2].sort_by { |i| i.size }.last` is equivalent to `[3, 1, 2].max_by { |i| i.size }`.
+  it 'does not register an offense when using `sort_by { |i| i.size }.last`' do
+    expect_no_offenses('[2, 1, 3].sort_by { |i| i.size }.last')
+  end
+
+  # `[2, 1, 3].sort_by(&:size).first` is not equivalent to `[2, 1, 3].first`, but this
   # cop would "correct" it to `[2, 1, 3].min_by`.
   it 'does not register an offense when sort_by is not given a block' do
     expect_no_offenses('[2, 1, 3].sort_by.first')