Adds better reusable error message support. Added to fetching remote

posts. /cc @riking

app/assets/javascripts/discourse/controllers/topic_controller.js

@@ -223,6 +223,8 @@ Discourse.TopicController = Discourse.ObjectController.extend(Discourse.Selected
       this.set('loadingExpanded', true);
       post.expand().then(function() {
         self.set('firstPostExpanded', true);
+      }).catch(function(error) {
+        bootbox.alert($.parseJSON(error.responseText).errors);
       }).finally(function() {
         self.set('loadingExpanded', false);
       });

app/controllers/application_controller.rb

@@ -5,10 +5,12 @@ require_dependency 'custom_renderer'
 require_dependency 'archetype'
 require_dependency 'rate_limiter'
 require_dependency 'crawler_detection'
+require_dependency 'json_error'
 
 class ApplicationController < ActionController::Base
   include CurrentUser
   include CanonicalURL::ControllerExtensions
+  include JsonError
 
   serialization_scope :guardian
 
@@ -242,11 +244,7 @@ class ApplicationController < ActionController::Base
     end
 
     def render_json_error(obj)
-      if obj.present?
+      render json: MultiJson.dump(create_errors_json(obj)), status: 422
-        render json: MultiJson.dump(errors: obj.errors.full_messages), status: 422
-      else
-        render json: MultiJson.dump(errors: [I18n.t('js.generic_error')]), status: 422
-      end
     end
 
     def success_json

app/controllers/posts_controller.rb

@@ -151,6 +151,8 @@ class PostsController < ApplicationController
       doc.content
     end
     render json: {cooked: content}
+  rescue
+    render_json_error I18n.t('errors.embed.load_from_remote')
   end
 
   def recover

config/locales/server.en.yml

@@ -28,6 +28,10 @@ en:
   via: "%{username} via %{site_name}"
   is_reserved: "is reserved"
 
+  errors:
+    embed:
+      load_from_remote: "There was an error loading that post."
+
   backup:
     operation_already_running: "An operation is currently running. Can't start a new job right now."
     backup_file_should_be_tar_gz: "The backup file should be a .tar.gz archive."

lib/json_error.rb

@@ -0,0 +1,21 @@
+module JsonError
+
+  def create_errors_json(obj)
+
+    # If we're passed a string, assume that is the error message
+    return {errors: [obj]} if obj.is_a?(String)
+
+    # If it looks like an activerecord object, extract its messages
+    return {errors: obj.errors.full_messages } if obj.respond_to?(:errors) && obj.errors.present?
+
+    # default to a generic error
+    JsonError.generic_error
+  end
+
+  private
+
+    def self.generic_error
+      {errors: [I18n.t('js.generic_error')]}
+    end
+
+end

spec/components/json_error_spec.rb

@@ -0,0 +1,55 @@
+require 'spec_helper'
+require_dependency 'json_error'
+
+shared_examples "a generic error" do
+  let(:result) { creator.create_errors_json(obj) }
+
+  it "should have a result object" do
+    result.should be_present
+  end
+
+  it "has a generic error message" do
+    result[:errors].should == [I18n.t('js.generic_error')]
+  end
+end
+
+describe JsonError do
+
+  let(:creator) { Object.new.extend(JsonError) }
+
+  describe "with a nil argument" do
+    it_behaves_like "a generic error" do
+      let(:obj) { nil }
+    end
+  end
+
+  describe "with an empty array" do
+    it_behaves_like "a generic error" do
+      let(:obj) { [] }
+    end
+  end
+
+  describe "with an activerecord object with no errors" do
+    it_behaves_like "a generic error" do
+      let(:obj) { Fabricate.build(:user) }
+    end
+  end
+
+  describe "with a string" do
+    it "returns the string in the error format" do
+      creator.create_errors_json("test error").should == {errors: ["test error"]}
+    end
+  end
+
+  describe "an activerecord objec with errors" do
+    let(:invalid_user) { User.new }
+    it "returns the errors correctly" do
+      invalid_user.should_not be_valid
+      result = creator.create_errors_json(invalid_user)
+      result.should be_present
+      result[:errors].should_not be_blank
+    end
+  end
+
+end
+