1 files changed, 57 insertions, 0 deletions
diff --git a/rubocop/cop/performance/ar_exists_and_present_blank.rb b/rubocop/cop/performance/ar_exists_and_present_blank.rb
new file mode 100644
index 00000000000..54c2d6bf95a
--- /dev/null
+++ b/rubocop/cop/performance/ar_exists_and_present_blank.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Performance
+      class ARExistsAndPresentBlank < RuboCop::Cop::Cop
+        def message_present(ivar)
+          "Avoid `#{ivar}.present?`, because it will generate database query 'Select TABLE.*' which is expensive. "\
+          "Suggest to use `#{ivar}.any?` to replace `#{ivar}.present?`"
+        end
+
+        def message_blank(ivar)
+          "Avoid `#{ivar}.blank?`, because it will generate database query 'Select TABLE.*' which is expensive. "\
+          "Suggest to use `#{ivar}.empty?` to replace `#{ivar}.blank?`"
+        end
+
+        def_node_matcher :exists_match, <<~PATTERN
+          (send (ivar $_) :exists?)
+        PATTERN
+
+        def_node_matcher :present_match, <<~PATTERN
+          (send (ivar $_) :present?)
+        PATTERN
+
+        def_node_matcher :blank_match, <<~PATTERN
+          (send (ivar $_) :blank?)
+        PATTERN
+
+        def file_name(node)
+          node.location.expression.source_buffer.name
+        end
+
+        def in_haml_file?(node)
+          file_name(node).end_with?('.haml.rb')
+        end
+
+        def on_send(node)
+          return unless in_haml_file?(node)
+
+          ivar_present = present_match(node)
+          ivar_blank = blank_match(node)
+          return unless ivar_present || ivar_blank
+
+          node.each_ancestor(:begin) do |begin_node|
+            begin_node.each_descendant do |n|
+              ivar_exists = exists_match(n)
+              next unless ivar_exists
+
+              add_offense(node, location: :expression, message: message_present(ivar_exists)) if ivar_exists == ivar_present
+              add_offense(node, location: :expression, message: message_blank(ivar_exists)) if ivar_exists == ivar_blank
+            end
+          end
+        end
+      end
+    end
+  end
+end