find railties and engines by name [4264 state:resolved]

Signed-off-by: José Valim <jose.valim@gmail.com>

railties/lib/rails/railtie.rb

@@ -32,6 +32,10 @@ def railtie_names
         subclasses.map { |p| p.railtie_name }
       end
 
+      def named(name)
+        subclasses.detect { |r| r.railtie_name == name }
+      end
+
       def log_subscriber(log_subscriber)
         Rails::LogSubscriber.add(railtie_name, log_subscriber)
       end

railties/test/railties/railtie_test.rb

@@ -15,6 +15,23 @@ def app
       @app ||= Rails.application
     end
 
+    test "can find railtie by name" do
+      class TieA < Rails::Railtie; railtie_name :railtie_a; end
+      class TieB < Rails::Railtie; railtie_name :railtie_b; end
+      class EngineA < Rails::Engine; engine_name :engine_a; end
+      class EngineB < Rails::Engine; engine_name :engine_b; end
+
+      assert_equal TieA, Rails::Railtie.named(:railtie_a)
+      assert_equal TieB, Rails::Railtie.named(:railtie_b)
+      assert_nil Rails::Railtie.named(:railtie_x)
+      assert_nil Rails::Railtie.named(:engine_a)
+
+      assert_equal EngineA, Rails::Engine.named(:engine_a)
+      assert_equal EngineB, Rails::Engine.named(:engine_b)
+      assert_nil Rails::Engine.named(:engine_x)
+      assert_nil Rails::Engine.named(:railtie_a)
+    end
+
     test "Rails::Railtie itself does not respond to config" do
       assert !Rails::Railtie.respond_to?(:config)
     end