WIP: specific error when calling DiscourseEvent.on outside of `plug…

…in.rb`

lib/rubocop/cop/discourse/plugins/discourse_event.rb

@@ -7,6 +7,8 @@ module Plugins
         class DiscourseEvent < Base
           MSG =
             "Use `on` instead of `DiscourseEvent.on` as the latter will listen to events even if the plugin is disabled."
+          NOT_OUTSIDE_PLUGIN_RB =
+            "Don’t call `DiscourseEvent.on` outside of `plugin.rb`."
           RESTRICT_ON_SEND = [:on].freeze
 
           def_node_matcher :discourse_event_on?, <<~MATCHER
@@ -15,7 +17,14 @@ class DiscourseEvent < Base
 
           def on_send(node)
             return unless discourse_event_on?(node)
-            add_offense(node, message: MSG)
+            return add_offense(node, message: MSG) if in_plugin_rb_file?
+            add_offense(node, message: NOT_OUTSIDE_PLUGIN_RB)
+          end
+
+          private
+
+          def in_plugin_rb_file?
+            processed_source.path.split("/").last == "plugin.rb"
           end
         end
       end

spec/lib/rubocop/cop/plugins/discourse_event_spec.rb

@@ -7,20 +7,33 @@
 
   let(:config) { RuboCop::Config.new }
 
-  context "when `DiscourseEvent.on` is called" do
-    it "registers an offense" do
-      expect_offense(<<~RUBY)
+  context "when outside `plugin.rb`" do
+    context "when `DiscourseEvent.on` is called" do
+      it "registers an offense" do
+        expect_offense(<<~RUBY, "another_file.rb")
+          DiscourseEvent.on(:topic_status_updated) { do_something }
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Discourse/Plugins/DiscourseEvent: Don’t call `DiscourseEvent.on` outside of `plugin.rb`.
+        RUBY
+      end
+    end
+  end
+
+  context "when inside `plugin.rb`" do
+    context "when `DiscourseEvent.on` is called" do
+      it "registers an offense" do
+        expect_offense(<<~RUBY, "plugin.rb")
         DiscourseEvent.on(:topic_status_updated) { do_something }
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Discourse/Plugins/DiscourseEvent: Use `on` instead of `DiscourseEvent.on` [...]
       RUBY
+      end
     end
-  end
 
-  context "when `on` is called" do
-    it "does not register an offense" do
-      expect_no_offenses(<<~RUBY)
+    context "when `on` is called" do
+      it "does not register an offense" do
+        expect_no_offenses(<<~RUBY, "plugin.rb")
         on(:topic_status_updated) { do_something }
       RUBY
+      end
     end
   end
 end