1 files changed, 45 insertions, 0 deletions
diff --git a/rubocop/cop/gitlab/has_many_through_scope.rb b/rubocop/cop/gitlab/has_many_through_scope.rb
new file mode 100644
index 00000000000..770a2a0529f
--- /dev/null
+++ b/rubocop/cop/gitlab/has_many_through_scope.rb
@@ -0,0 +1,45 @@
+require 'gitlab/styles/rubocop/model_helpers'
+
+module RuboCop
+  module Cop
+    module Gitlab
+      class HasManyThroughScope < RuboCop::Cop::Cop
+        include ::Gitlab::Styles::Rubocop::ModelHelpers
+
+        MSG = 'Always provide an explicit scope calling auto_include(false) when using has_many :through'.freeze
+
+        def_node_search :through?, <<~PATTERN
+          (pair (sym :through) _)
+        PATTERN
+
+        def_node_matcher :has_many_through?, <<~PATTERN
+          (send nil? :has_many ... #through?)
+        PATTERN
+
+        def_node_search :disables_auto_include?, <<~PATTERN
+          (send _ :auto_include false)
+        PATTERN
+
+        def_node_matcher :scope_disables_auto_include?, <<~PATTERN
+          (block (send nil? :lambda) _ #disables_auto_include?)
+        PATTERN
+
+        def on_send(node)
+          return unless in_model?(node)
+          return unless has_many_through?(node)
+
+          target = node
+          scope_argument = node.children[3]
+
+          if scope_argument.children[0].children.last == :lambda
+            return if scope_disables_auto_include?(scope_argument)
+
+            target = scope_argument
+          end
+
+          add_offense(target, location: :expression)
+        end
+      end
+    end
+  end
+end