Inject Rails' channel paths in engine.

We were explicitly referencing Rails.root in ActionCable::Server::Configuration.initialize,
thereby coupling ourselves to Rails.

Instead add `app/channels` to Rails' app paths and assign the existent files
to `channel_paths`.

Users can still append to those load paths with `<<` and `push` in `config/application.rb`.

This means we can remove the custom `Dir` lookup in `channel_paths` and the Rails
and root definitions in the tests.

actioncable/lib/action_cable/engine.rb

@@ -31,6 +31,8 @@ class Railtie < Rails::Engine # :nodoc:
           self.cable = Rails.application.config_for(config_path).with_indifferent_access
         end
 
+        self.channel_paths = Rails.application.paths['app/channels'].existent
+
         options.each { |k,v| send("#{k}=", v) }
       end
     end

actioncable/lib/action_cable/server/configuration.rb

@@ -5,27 +5,20 @@ module Server
     class Configuration
       attr_accessor :logger, :log_tags
       attr_accessor :connection_class, :worker_pool_size
-      attr_accessor :channel_load_paths
       attr_accessor :disable_request_forgery_protection, :allowed_request_origins
       attr_accessor :cable, :url
 
+      attr_accessor :channel_paths # :nodoc:
+
       def initialize
         @log_tags = []
 
         @connection_class  = ApplicationCable::Connection
         @worker_pool_size  = 100
 
-        @channel_load_paths = [Rails.root.join('app/channels')]
-
         @disable_request_forgery_protection = false
       end
 
-      def channel_paths
-        @channel_paths ||= channel_load_paths.flat_map do |path|
-          Dir["#{path}/**/*_channel.rb"]
-        end
-      end
-
       def channel_class_names
         @channel_class_names ||= channel_paths.collect do |channel_path|
           Pathname.new(channel_path).basename.to_s.split('.').first.camelize

actioncable/test/client_test.rb

@@ -16,20 +16,16 @@ def setup
     ::Object.const_set(:ApplicationCable, Module.new)
     ::ApplicationCable.const_set(:Connection, Class.new(ActionCable::Connection::Base))
 
-    ::Object.const_set(:Rails, Module.new)
-    ::Rails.singleton_class.send(:define_method, :root) { Pathname.new(__dir__) }
-
     ActionCable.instance_variable_set(:@server, nil)
     server = ActionCable.server
-    server.config = ActionCable::Server::Configuration.new
     inner_logger = Logger.new(StringIO.new).tap { |l| l.level = Logger::UNKNOWN }
     server.config.logger = ActionCable::Connection::TaggedLoggerProxy.new(inner_logger, tags: [])
 
     server.config.cable = { adapter: 'async' }.with_indifferent_access
 
     # and now the "real" setup for our test:
     server.config.disable_request_forgery_protection = true
-    server.config.channel_load_paths = [File.expand_path('client', __dir__)]
+    server.config.channel_paths = [ File.expand_path('client/echo_channel.rb', __dir__) ]
 
     Thread.new { EventMachine.run } unless EventMachine.reactor_running?
     Thread.pass until EventMachine.reactor_running?
@@ -45,10 +41,6 @@ def teardown
       ::Object.send(:remove_const, :ApplicationCable)
     rescue NameError
     end
-    begin
-      ::Object.send(:remove_const, :Rails)
-    rescue NameError
-    end
   end
 
   def with_puma_server(rack_app = ActionCable.server, port = 3099)

actioncable/test/subscription_adapter/common.rb

@@ -13,11 +13,7 @@ def setup
     ::Object.const_set(:ApplicationCable, Module.new)
     ::ApplicationCable.const_set(:Connection, Class.new(ActionCable::Connection::Base))
 
-    ::Object.const_set(:Rails, Module.new)
-    ::Rails.singleton_class.send(:define_method, :root) { Pathname.new(__dir__) }
-
     server = ActionCable::Server::Base.new
-    server.config = ActionCable::Server::Configuration.new
     inner_logger = Logger.new(StringIO.new).tap { |l| l.level = Logger::UNKNOWN }
     server.config.logger = ActionCable::Connection::TaggedLoggerProxy.new(inner_logger, tags: [])
 
@@ -39,10 +35,6 @@ def teardown
       ::Object.send(:remove_const, :ApplicationCable)
     rescue NameError
     end
-    begin
-      ::Object.send(:remove_const, :Rails)
-    rescue NameError
-    end
   end
 
 

railties/lib/rails/engine/configuration.rb

@@ -39,6 +39,7 @@ def paths
           paths.add "app",                 eager_load: true, glob: "{*,*/concerns}"
           paths.add "app/assets",          glob: "*"
           paths.add "app/controllers",     eager_load: true
+          paths.add "app/channels",        eager_load: true, glob: "**/*_channel.rb"
           paths.add "app/helpers",         eager_load: true
           paths.add "app/models",          eager_load: true
           paths.add "app/mailers",         eager_load: true