Merge branch 'demodulize-model-headers' into 'master'

Demodulize model headers in emails

See merge request gitlab-org/gitlab-ce!31968

app/mailers/notify.rb

@@ -125,9 +125,8 @@ class Notify < BaseMailer
   def mail_thread(model, headers = {})
     add_project_headers
     add_unsubscription_headers_and_links
+    add_model_headers(model)
 
-    headers["X-GitLab-#{model.class.name}-ID"] = model.id
-    headers["X-GitLab-#{model.class.name}-IID"] = model.iid if model.respond_to?(:iid)
     headers['X-GitLab-Reply-Key'] = reply_key
 
     @reason = headers['X-GitLab-NotificationReason']
@@ -196,6 +195,18 @@ class Notify < BaseMailer
     @reply_key ||= SentNotification.reply_key
   end
 
+  # This method applies threading headers to the email to identify
+  # the instance we are discussing.
+  #
+  # All model instances must have `#id`, and may implement `#iid`.
+  def add_model_headers(object)
+    # Use replacement so we don't strip the module.
+    prefix = "X-GitLab-#{object.class.name.gsub(/::/, '-')}"
+
+    headers["#{prefix}-ID"] = object.id
+    headers["#{prefix}-IID"] = object.iid if object.respond_to?(:iid)
+  end
+
   def add_project_headers
     return unless @project
 

spec/mailers/notify_spec.rb

@@ -543,6 +543,73 @@ describe Notify do
       end
     end
 
+    describe '#mail_thread' do
+      set(:mail_thread_note) { create(:note) }
+
+      let(:headers) do
+        {
+          from: 'someone@test.com',
+          to: 'someone-else@test.com',
+          subject: 'something',
+          template_name: '_note_email' # re-use this for testing
+        }
+      end
+
+      let(:mailer) do
+        mailer = described_class.new
+        mailer.instance_variable_set(:@note, mail_thread_note)
+        mailer
+      end
+
+      context 'the model has no namespace' do
+        class TopLevelThing
+          include Referable
+          include Noteable
+
+          def to_reference(*_args)
+            'tlt-ref'
+          end
+
+          def id
+            'tlt-id'
+          end
+        end
+
+        subject do
+          mailer.send(:mail_thread, TopLevelThing.new, headers)
+        end
+
+        it 'has X-GitLab-Namespaced-Thing-ID header' do
+          expect(subject.header['X-GitLab-TopLevelThing-ID'].value).to eq('tlt-id')
+        end
+      end
+
+      context 'the model has a namespace' do
+        module Namespaced
+          class Thing
+            include Referable
+            include Noteable
+
+            def to_reference(*_args)
+              'some-reference'
+            end
+
+            def id
+              'some-id'
+            end
+          end
+        end
+
+        subject do
+          mailer.send(:mail_thread, Namespaced::Thing.new, headers)
+        end
+
+        it 'has X-GitLab-Namespaced-Thing-ID header' do
+          expect(subject.header['X-GitLab-Namespaced-Thing-ID'].value).to eq('some-id')
+        end
+      end
+    end
+
     context 'for issue notes' do
       let(:host) { Gitlab.config.gitlab.host }