[Fix rubocop#437] Fix a false positive for `Performance/ChainArrayAll…

…ocation`

Fixes rubocop#437.

This PR fixes a false positive for `Performance/ChainArrayAllocation`
when using `select` with block argument after `select`.

changelog/fix_a_false_positive_for_performance_chain_array_allocation.md

@@ -0,0 +1 @@
+* [#437](https://github.com/rubocop/rubocop-performance/issues/437): Fix a false positive for `Performance/ChainArrayAllocation` when using `select` with block argument after `select`. ([@koic][])

lib/rubocop/cop/performance/chain_array_allocation.rb

@@ -63,6 +63,10 @@ def on_send(node)
           chain_array_allocation?(node) do |fm, sm|
             return if node.each_descendant(:send).any? { |descendant| descendant.method?(:lazy) }
 
+            # NOTE: `QueryMethods#select` in Rails accepts positional arguments, whereas `Enumerable#select` does not.
+            #        This difference can be utilized to reduce the knowledge requirements related to `select`.
+            return if node.method?(:select) && node.arguments.any?
+
             range = range_between(node.loc.dot.begin_pos, node.source_range.end_pos)
 
             add_offense(range, message: format(MSG, method: fm, second_method: sm))

spec/rubocop/cop/performance/chain_array_allocation_spec.rb

@@ -53,4 +53,21 @@
       RUBY
     end
   end
+
+  describe 'when using `select` with block argument after `select`' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        model.select(:foo, :bar).select { |item| item.do_something }
+                                ^^^^^^^ Use unchained `select` and `select!` (followed by `return array` if required) instead of chaining `select...select`.
+      RUBY
+    end
+  end
+
+  describe 'when using `select` with positional arguments after `select`' do
+    it 'does not register an offense' do
+      expect_no_offenses(<<~RUBY)
+        model.select(:foo, :bar).select(:baz, :qux)
+      RUBY
+    end
+  end
 end