FIX: rescue specific errors on invite failure

app/controllers/invites_controller.rb

@@ -74,7 +74,7 @@ class InvitesController < ApplicationController
       else
         render json: failed_json, status: 422
       end
-    rescue => e
+    rescue Invite::UserExists => e
       render json: {errors: [e.message]}, status: 422
     end
   end

app/controllers/topics_controller.rb

@@ -497,7 +497,7 @@ class TopicsController < ApplicationController
       else
         render json: failed_json, status: 422
       end
-    rescue => e
+    rescue Topic::UserExists => e
       render json: {errors: [e.message]}, status: 422
     end
   end

app/models/invite.rb

@@ -1,6 +1,7 @@
 require_dependency 'rate_limiter'
 
 class Invite < ActiveRecord::Base
+  class UserExists < StandardError; end
   include RateLimiter::OnCreateRecord
   include Trashable
 
@@ -103,7 +104,7 @@ class Invite < ActiveRecord::Base
 
     if user
       extend_permissions(topic, user, invited_by) if topic
-      raise StandardError.new I18n.t("invite.user_exists", email: lower_email, username: user.username)
+      raise UserExists.new I18n.t("invite.user_exists", email: lower_email, username: user.username)
     end
 
     invite = Invite.with_deleted

app/models/topic.rb

@@ -10,6 +10,7 @@ require_dependency 'discourse_tagging'
 require_dependency 'search'
 
 class Topic < ActiveRecord::Base
+  class UserExists < StandardError; end
   include ActionView::Helpers::SanitizeHelper
   include RateLimiter::OnCreateRecord
   include HasCustomFields
@@ -722,7 +723,7 @@ SQL
     if private_message?
       # If the user exists, add them to the message.
       user = User.find_by_username_or_email(username_or_email)
-      raise StandardError.new I18n.t("topic_invite.user_exists") if user.present? && topic_allowed_users.where(user_id: user.id).exists?
+      raise UserExists.new I18n.t("topic_invite.user_exists") if user.present? && topic_allowed_users.where(user_id: user.id).exists?
 
       if user && topic_allowed_users.create!(user_id: user.id)
         # Create a small action message
@@ -747,7 +748,7 @@ SQL
     else
       # invite existing member to a topic
       user = User.find_by_username(username_or_email)
-      raise StandardError.new I18n.t("topic_invite.user_exists") if user.present? && topic_allowed_users.where(user_id: user.id).exists?
+      raise UserExists.new I18n.t("topic_invite.user_exists") if user.present? && topic_allowed_users.where(user_id: user.id).exists?
 
       if user && topic_allowed_users.create!(user_id: user.id)
         # rate limit topic invite

spec/models/invite_spec.rb

@@ -162,7 +162,7 @@ describe Invite do
 
     it "works" do
       # doesn't create an invite
-      expect { topic.invite_by_email(topic.user, coding_horror.email) }.to raise_error(StandardError)
+      expect { topic.invite_by_email(topic.user, coding_horror.email) }.to raise_error(Invite::UserExists)
 
       # gives the user permission to access the topic
       expect(topic.allowed_users.include?(coding_horror)).to eq(true)

spec/models/topic_spec.rb

@@ -1678,7 +1678,7 @@ describe Topic do
 
       it "should add user to the group" do
         expect(Guardian.new(walter).can_see?(group_private_topic)).to be_falsey
-        expect { group_private_topic.invite(group_manager, walter.email) }.to raise_error(StandardError)
+        expect { group_private_topic.invite(group_manager, walter.email) }.to raise_error(Invite::UserExists)
         expect(walter.groups).to include(group)
         expect(Guardian.new(walter).can_see?(group_private_topic)).to be_truthy
       end