users: lock out users with invalid names until they change their name.

Forcibly redirect users to the name change page if their name is
invalid. This means user with invalid names can't do anything or view
any pages until they change their name. API requests are still allowed.

app/controllers/application_controller.rb

@@ -15,6 +15,7 @@ class ApplicationController < ActionController::Base
   before_action :set_variant
   before_action :add_headers
   before_action :cause_error
+  before_action :redirect_if_name_invalid?
   after_action :skip_session_if_publicly_cached
   after_action :reset_current_user
   layout "default"
@@ -198,6 +199,13 @@ class ApplicationController < ActionController::Base
     render_error_page(status, error)
   end
 
+  def redirect_if_name_invalid?
+    if request.format.html? && CurrentUser.user.name_invalid?
+      flash[:notice] = "You must change your username to continue using #{Danbooru.config.app_name}"
+      redirect_to new_user_name_change_request_path
+    end
+  end
+
   def ip_ban_check
     raise User::PrivilegeError if !request.get? && IpBan.hit!(:full, CurrentUser.ip_addr)
   end

app/controllers/user_name_change_requests_controller.rb

@@ -3,6 +3,8 @@
 class UserNameChangeRequestsController < ApplicationController
   respond_to :html, :json, :xml
 
+  skip_before_action :redirect_if_name_invalid?
+
   def new
     @change_request = authorize UserNameChangeRequest.new(permitted_attributes(UserNameChangeRequest))
     respond_with(@change_request)

test/functional/application_controller_test.rb

@@ -76,13 +76,12 @@ class ApplicationControllerTest < ActionDispatch::IntegrationTest
     end
 
     context "when a user has an invalid username" do
-      should "show a warning banner" do
+      should "redirect to the name change page" do
         @user = create(:user)
         @user.update_columns(name: "foo__bar")
 
         get_auth posts_path, @user
-        assert_response :success
-        assert_select "#invalid-name-notice"
+        assert_redirected_to new_user_name_change_request_path
       end
     end