Support for custom messages and redirects when creating posts (#8434)

* Support for custom messages and redirects when creating posts

When a post/topic is created Discourse serializes a `NewPostResult`
object. Normally this contains a status like `created_post` or
errors describing why the post could not be created.

There are times when a plugin might want to take the inputted post
and do something in the background. In this case, the plugin
can return a custom `message` and `route_to` attribute in the
`NewPostResult`.

If present, the message will be displayed in an alert, and when "Ok" is
clicked the user will be routed to the new URL.

* Destroy the draft in parallel

app/assets/javascripts/discourse/controllers/composer.js.es6

@@ -709,6 +709,17 @@ export default Controller.extend({
         if (result.responseJson.action === "create_post") {
           this.appEvents.trigger("post:highlight", result.payload.post_number);
         }
+
+        if (result.responseJson.route_to) {
+          this.destroyDraft();
+          if (result.responseJson.message) {
+            return bootbox.alert(result.responseJson.message, () => {
+              DiscourseURL.routeTo(result.responseJson.route_to);
+            });
+          }
+          return DiscourseURL.routeTo(result.responseJson.route_to);
+        }
+
         this.close();
 
         const currentUser = this.currentUser;

app/serializers/new_post_result_serializer.rb

@@ -6,7 +6,9 @@ class NewPostResultSerializer < ApplicationSerializer
              :errors,
              :success,
              :pending_count,
-             :reason
+             :reason,
+             :message,
+             :route_to
 
   has_one :pending_post, serializer: TopicPendingPostSerializer, root: false, embed: :objects
 
@@ -64,4 +66,20 @@ class NewPostResultSerializer < ApplicationSerializer
     pending_count.present?
   end
 
+  def route_to
+    object.route_to
+  end
+
+  def include_route_to?
+    object.route_to.present?
+  end
+
+  def message
+    object.message
+  end
+
+  def include_message?
+    object.message.present?
+  end
+
 end

lib/new_post_result.rb

@@ -9,6 +9,8 @@ class NewPostResult
   attr_accessor :post
   attr_accessor :reviewable
   attr_accessor :pending_count
+  attr_accessor :route_to
+  attr_accessor :message
 
   def initialize(action, success = false)
     @action = action

spec/serializers/new_post_result_serializer_spec.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe NewPostResultSerializer do
+
+  it "includes the message and route_to if present" do
+    result = NewPostResult.new(:custom, true)
+    result.message = 'hello :)'
+    result.route_to = "/cool-route"
+
+    serializer = described_class.new(result)
+    expect(serializer.success).to eq(true)
+    expect(serializer.message).to eq('hello :)')
+    expect(serializer.route_to).to eq('/cool-route')
+  end
+end

test/javascripts/acceptance/composer-test.js.es6

@@ -234,6 +234,26 @@ QUnit.test("Create an enqueued Topic", async assert => {
   assert.ok(invisible(".d-modal"), "the modal can be dismissed");
 });
 
+QUnit.test("Can display a message and route to a URL", async assert => {
+  await visit("/");
+  await click("#create-topic");
+  await fillIn("#reply-title", "This title doesn't matter");
+  await fillIn(".d-editor-input", "custom message");
+  await click("#reply-control button.create");
+  assert.equal(
+    find(".bootbox .modal-body").text(),
+    "This is a custom response"
+  );
+  assert.equal(currentURL(), "/", "it doesn't change routes");
+
+  await click(".bootbox .btn-primary");
+  assert.equal(
+    currentURL(),
+    "/faq",
+    "can navigate to a `route_to` destination"
+  );
+});
+
 QUnit.test("Create a Reply", async assert => {
   await visit("/t/internationalization-localization/280");
 

test/javascripts/helpers/create-pretender.js.es6

@@ -497,6 +497,15 @@ export default function() {
         });
       }
 
+      if (data.raw === "custom message") {
+        return response(200, {
+          success: true,
+          action: "custom",
+          message: "This is a custom response",
+          route_to: "/faq"
+        });
+      }
+
       return response(200, {
         success: true,
         action: "create_post",