1 files changed, 71 insertions, 0 deletions
diff --git a/rubocop/cop/gitlab/event_store_subscriber.rb b/rubocop/cop/gitlab/event_store_subscriber.rb
new file mode 100644
index 00000000000..0b2dd94bc42
--- /dev/null
+++ b/rubocop/cop/gitlab/event_store_subscriber.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Gitlab
+      # Cop that checks the implementation of Gitlab::EventStore::Subscriber
+      #
+      # A worker that implements Gitlab::EventStore::Subscriber
+      # must implement the method #handle_event(event) and
+      # must not override the method #perform(*args)
+      #
+      #  # bad
+      #  class MySubscriber
+      #    include Gitlab::EventStore::Subscriber
+      #
+      #    def perform(*args)
+      #    end
+      #  end
+      #
+      #  # bad
+      #  class MySubscriber
+      #    include Gitlab::EventStore::Subscriber
+      #  end
+      #
+      #  # good
+      #  class MySubscriber
+      #    include Gitlab::EventStore::Subscriber
+      #
+      #    def handle_event(event)
+      #    end
+      #  end
+      #
+      class EventStoreSubscriber < RuboCop::Cop::Cop
+        SUBSCRIBER_MODULE_NAME = 'Gitlab::EventStore::Subscriber'
+        FORBID_PERFORM_OVERRIDE = "Do not override `perform` in a `#{SUBSCRIBER_MODULE_NAME}`."
+        REQUIRE_HANDLE_EVENT = "A `#{SUBSCRIBER_MODULE_NAME}` must implement `#handle_event(event)`."
+
+        def_node_matcher :includes_subscriber?, <<~PATTERN
+          (send nil? :include (const (const (const nil? :Gitlab) :EventStore) :Subscriber))
+        PATTERN
+
+        def on_send(node)
+          return unless includes_subscriber?(node)
+
+          self.is_subscriber ||= true
+          self.include_subscriber_node ||= node
+        end
+
+        def on_def(node)
+          if is_subscriber && node.method_name == :perform
+            add_offense(node, message: FORBID_PERFORM_OVERRIDE)
+          end
+
+          self.implements_handle_event ||= true if node.method_name == :handle_event
+        end
+
+        def on_investigation_end
+          super
+
+          if is_subscriber && !implements_handle_event
+            add_offense(include_subscriber_node, message: REQUIRE_HANDLE_EVENT)
+          end
+        end
+
+        private
+
+        attr_accessor :is_subscriber, :include_subscriber_node, :implements_handle_event
+      end
+    end
+  end
+end