FIX: include topic title and domain name in topic invite mail

app/mailers/invite_mailer.rb

@@ -24,6 +24,7 @@ class InviteMailer < ActionMailer::Base
       build_email(invite.email,
                   template: 'invite_mailer',
                   invitee_name: invitee_name,
+                  site_domain_name: Discourse.current_hostname,
                   invite_link: "#{Discourse.base_url}/invites/#{invite.invite_key}",
                   topic_title: first_topic.try(:title),
                   topic_excerpt: topic_excerpt,

config/locales/server.en.yml

@@ -1048,7 +1048,7 @@ en:
       blocked: "is blocked."
 
   invite_mailer:
-    subject_template: "%{invitee_name} invited you to a discussion at %{site_name}"
+    subject_template: "%{invitee_name} invited you to '%{topic_title}' on %{site_domain_name}"
     text_body_template: |
       %{invitee_name} invited you to a discussion
 

spec/mailers/invite_mailer_spec.rb

@@ -42,6 +42,14 @@ describe InviteMailer do
         expect(invite_mail.subject).to be_present
       end
 
+      it 'renders topic title in subject' do
+        expect(invite_mail.subject).to match(topic.title)
+      end
+
+      it 'renders site domain name in subject' do
+        expect(invite_mail.subject).to match(Discourse.current_hostname)
+      end
+
       it 'renders the body' do
         expect(invite_mail.body).to be_present
       end