FIX: better error message when invited user already exists

app/assets/javascripts/discourse/templates/modal/invite.hbs

@@ -2,7 +2,7 @@
   {{#if model.error}}
     <div class="alert alert-error">
       <button class="close" data-dismiss="alert">×</button>
-      {{errorMessage}}
+      {{{errorMessage}}}
     </div>
   {{/if}}
   {{#if model.finished}}

app/models/invite.rb

@@ -103,7 +103,7 @@ class Invite < ActiveRecord::Base
 
     if user
       extend_permissions(topic, user, invited_by) if topic
-      return nil
+      raise StandardError.new I18n.t("invite.user_exists", email: lower_email, username: user.username)
     end
 
     invite = Invite.with_deleted

config/locales/server.en.yml

@@ -138,6 +138,7 @@ en:
 
   invite:
     not_found: "Your invite token is invalid. Please contact the site's administrator."
+    user_exists: "There's no need to invite <b>%{email}</b>, they <a href='/users/%{username}/summary'>already have an account!</a>"
 
   bulk_invite:
     file_should_be_csv: "The uploaded file should be of csv format."

spec/models/invite_spec.rb

@@ -152,11 +152,10 @@ describe Invite do
   context 'an existing user' do
     let(:topic) { Fabricate(:topic, category_id: nil, archetype: 'private_message') }
     let(:coding_horror) { Fabricate(:coding_horror) }
-    let!(:invite) { topic.invite_by_email(topic.user, coding_horror.email) }
 
     it "works" do
       # doesn't create an invite
-      expect(invite).to be_blank
+      expect { topic.invite_by_email(topic.user, coding_horror.email) }.to raise_error(StandardError)
 
       # gives the user permission to access the topic
       expect(topic.allowed_users.include?(coding_horror)).to eq(true)

spec/models/topic_spec.rb

@@ -1773,8 +1773,7 @@ describe Topic do
 
       it "should add user to the group" do
         expect(Guardian.new(walter).can_see?(group_private_topic)).to be_falsey
-        invite = group_private_topic.invite(group_manager, walter.email)
-        expect(invite).to be_nil
+        expect { group_private_topic.invite(group_manager, walter.email) }.to raise_error(StandardError)
         expect(walter.groups).to include(group)
         expect(Guardian.new(walter).can_see?(group_private_topic)).to be_truthy
       end