Do not load ActiveJobs if ActiveJob is not loaded (#602)

* Do not load ActiveJobs if ActiveJob is not loaded

* Do not include Broadcastable in ActiveRecord::Base if ActiveJob is not loaded

app/models/concerns/turbo/broadcastable.rb

@@ -1,4 +1,4 @@
-# Turbo streams can be broadcasted directly from models that include this module (this is automatically done for Active Records).
+# Turbo streams can be broadcasted directly from models that include this module (this is automatically done for Active Records if ActiveJob is loaded).
 # This makes it convenient to execute both synchronous and asynchronous updates, and render directly from callbacks in models
 # or from controllers or jobs that act on those models. Here's an example:
 #

lib/turbo/engine.rb

@@ -15,6 +15,27 @@ class Engine < Rails::Engine
       #{root}/app/jobs
     )
 
+    # If the parent application does not use Active Job, app/jobs cannot
+    # be eager loaded, because it references the ActiveJob constant.
+    #
+    # When turbo-rails depends on Rails 7 or above, the entire block can be
+    # reduced to
+    #
+    #   unless defined?(ActiveJob)
+    #     Rails.autoloaders.once.do_not_eager_load("#{root}/app/jobs")
+    #   end
+    #
+    initializer "turbo.no_active_job", before: :set_eager_load_paths do
+      unless defined?(ActiveJob)
+        if Rails.autoloaders.zeitwerk_enabled?
+          Rails.autoloaders.once.do_not_eager_load("#{root}/app/jobs")
+        else
+          # This else branch only runs in Rails 6.x + classic mode.
+          config.eager_load_paths.delete("#{root}/app/jobs")
+        end
+      end
+    end
+
     # If the parent application does not use Action Cable, app/channels cannot
     # be eager loaded, because it references the ActionCable constant.
     #
@@ -70,8 +91,10 @@ class Engine < Rails::Engine
     end
 
     initializer "turbo.broadcastable" do
-      ActiveSupport.on_load(:active_record) do
-        include Turbo::Broadcastable
+      ActiveSupport.on_load(:active_job) do
+        ActiveSupport.on_load(:active_record) do
+          include Turbo::Broadcastable
+        end
       end
     end
 
@@ -99,10 +122,12 @@ class Engine < Rails::Engine
         include Turbo::TestAssertions
       end
 
-      ActiveSupport.on_load(:action_cable) do
-        ActiveSupport.on_load(:active_support_test_case) do
-          require "turbo/broadcastable/test_helper"
-          include Turbo::Broadcastable::TestHelper
+      ActiveSupport.on_load(:active_job) do
+        ActiveSupport.on_load(:action_cable) do
+          ActiveSupport.on_load(:active_support_test_case) do
+            require "turbo/broadcastable/test_helper"
+            include Turbo::Broadcastable::TestHelper
+          end
         end
       end