UX: Add group name to error message (#11333)

The group name used to be part of the error message, but was removed
in a past commit.

app/controllers/application_controller.rb

@@ -207,6 +207,7 @@ class ApplicationController < ActionController::Base
       403,
       include_ember: true,
       custom_message: e.custom_message,
+      custom_message_params: e.custom_message_params,
       group: e.group
     )
   end

app/controllers/topics_controller.rb

@@ -112,6 +112,7 @@ class TopicsController < ApplicationController
             'not in group',
             ex.obj,
             custom_message: 'not_in_group.title_topic',
+            custom_message_params: { group: group.name },
             group: group
           )
         end

config/locales/server.en.yml

@@ -281,7 +281,7 @@ en:
   email_template_cant_be_modified: "This email template can't be modified"
   invalid_whisper_access: "Either whispers are not enabled or you do not have access to create whisper posts"
   not_in_group:
-    title_topic: "You must be in a group to see this topic."
+    title_topic: "You need to request membership to the '%{group}' group to see this topic."
     title_category: "You must be in a group to see this category."
     request_membership: "Request Membership"
     join_group: "Join Group"

lib/discourse.rb

@@ -142,6 +142,7 @@ module Discourse
     attr_reader :obj
     attr_reader :opts
     attr_reader :custom_message
+    attr_reader :custom_message_params
     attr_reader :group
 
     def initialize(msg = nil, obj = nil, opts = nil)
@@ -150,6 +151,7 @@ module Discourse
       @opts = opts || {}
       @obj = obj
       @custom_message = opts[:custom_message] if @opts[:custom_message]
+      @custom_message_params = opts[:custom_message_params] if @opts[:custom_message_params]
       @group = opts[:group] if @opts[:group]
     end
   end

spec/requests/topics_controller_spec.rb

@@ -1584,6 +1584,30 @@ RSpec.describe TopicsController do
       end
     end
 
+    describe 'when topic is allowed to a group' do
+      let(:group) { Fabricate(:group, public_admission: true) }
+      let(:category) do
+        Fabricate(:category_with_definition).tap do |category|
+          category.set_permissions(group => :full)
+          category.save!
+        end
+      end
+      let(:topic) { Fabricate(:topic, category: category) }
+
+      before do
+        SiteSetting.detailed_404 = true
+      end
+
+      it 'shows a descriptive error message containing the group name' do
+        get "/t/#{topic.id}.json"
+
+        html = CGI.unescapeHTML(response.parsed_body["extras"]["html"])
+        expect(response.status).to eq(403)
+        expect(html).to include(I18n.t('not_in_group.title_topic', group: group.name))
+        expect(html).to include(I18n.t('not_in_group.join_group'))
+      end
+    end
+
     it 'correctly renders canoicals' do
       get "/t/#{topic.id}", params: { slug: topic.slug }