1 files changed, 32 insertions, 0 deletions
diff --git a/rubocop/cop/performance/readlines_each.rb b/rubocop/cop/performance/readlines_each.rb
new file mode 100644
index 00000000000..cb4ffaca6e9
--- /dev/null
+++ b/rubocop/cop/performance/readlines_each.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Performance
+      class ReadlinesEach < RuboCop::Cop::Cop
+        MESSAGE = 'Avoid `IO.readlines.each`, since it reads contents into memory in full. ' \
+          'Use `IO.each_line` or `IO.each` instead.'
+
+        def_node_matcher :full_file_read_via_class?, <<~PATTERN
+          (send
+            (send (const nil? {:IO :File}) :readlines _) :each)
+        PATTERN
+
+        def_node_matcher :full_file_read_via_instance?, <<~PATTERN
+          (... (... :readlines) :each)
+        PATTERN
+
+        def on_send(node)
+          full_file_read_via_class?(node) { add_offense(node, location: :selector, message: MESSAGE) }
+          full_file_read_via_instance?(node) { add_offense(node, location: :selector, message: MESSAGE) }
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            corrector.replace(node.loc.expression, node.source.gsub('readlines.each', 'each_line'))
+          end
+        end
+      end
+    end
+  end
+end