Move debugger into middleware

railties/lib/commands/server.rb

@@ -83,22 +83,11 @@
   app = Rack::Builder.new {
     use Rails::Rack::Logger
     use Rails::Rack::Static
+    use Rails::Rack::Debugger if options[:debugger]
     run ActionController::Dispatcher.new
   }.to_app
 end
 
-if options[:debugger]
-  begin
-    require_library_or_gem 'ruby-debug'
-    Debugger.start
-    Debugger.settings[:autoeval] = true if Debugger.respond_to?(:settings)
-    puts "=> Debugger enabled"
-  rescue Exception
-    puts "You need to install ruby-debug to run the server in debugging mode. With gems, use 'gem install ruby-debug'"
-    exit
-  end
-end
-
 puts "=> Call with -d to detach"
 
 trap(:INT) { exit }

railties/lib/rails/rack.rb

 module Rails
   module Rack
+    autoload :Debugger, "rails/rack/debugger"
     autoload :Logger, "rails/rack/logger"
     autoload :Static, "rails/rack/static"
   end

railties/lib/rails/rack/debugger.rb

+module Rails
+  module Rack
+    class Debugger
+      def initialize(app)
+        @app = app
+
+        require_library_or_gem 'ruby-debug'
+        ::Debugger.start
+        ::Debugger.settings[:autoeval] = true if ::Debugger.respond_to?(:settings)
+        puts "=> Debugger enabled"
+      rescue Exception
+        puts "You need to install ruby-debug to run the server in debugging mode. With gems, use 'gem install ruby-debug'"
+        exit
+      end
+
+      def call(env)
+        @app.call(env)
+      end
+    end
+  end
+end