add tests and external file backtrace for Routing::Mapper#draw

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -1336,10 +1336,11 @@ module ActionDispatch
             msg  = "Your router tried to #draw the external file #{name}.rb,\n" \
                    "but the file was not found in:\n\n"
             msg += @draw_paths.map { |_path| " * #{_path}" }.join("\n")
-            raise msg
+            raise ArgumentError, msg
           end
-
-          instance_eval(path.join("#{name}.rb").read)
+          
+          route_path = path.join("#{name}.rb")
+          instance_eval(route_path.read, route_path.to_s)
         end
 
         # match 'path' => 'controller#action'

actionpack/test/dispatch/routing_test.rb

@@ -2324,6 +2324,55 @@ class TestNamespaceWithControllerOption < ActionDispatch::IntegrationTest
   end
 end
 
+class TestDrawExternalFile < ActionDispatch::IntegrationTest
+  class ExternalController < ActionController::Base
+    def index
+      render :text => "external#index"
+    end
+  end
+
+  DRAW_PATH = Pathname.new(File.expand_path('../../fixtures/routes', __FILE__))
+
+  DefaultScopeRoutes = ActionDispatch::Routing::RouteSet.new.tap do |app|
+    app.draw_paths << DRAW_PATH
+  end
+
+  def app
+    DefaultScopeRoutes
+  end
+
+  def test_draw_external_file
+    DefaultScopeRoutes.draw do
+      scope :module => 'test_draw_external_file' do
+        draw :external
+      end
+    end
+
+    get '/external'
+    assert_equal "external#index", @response.body
+  end
+
+  def test_draw_nonexistent_file
+    exception = assert_raise ArgumentError do
+      DefaultScopeRoutes.draw do
+        draw :nonexistent
+      end
+    end
+    assert_match 'Your router tried to #draw the external file nonexistent.rb', exception.message
+    assert_match DRAW_PATH.to_s, exception.message
+  end
+
+  def test_draw_bogus_file
+    exception = assert_raise NoMethodError do
+      DefaultScopeRoutes.draw do
+        draw :bogus
+      end
+    end
+    assert_match "undefined method `wrong'", exception.message
+    assert_match 'test/fixtures/routes/bogus.rb:1', exception.backtrace.first
+  end
+end
+
 class TestDefaultScope < ActionDispatch::IntegrationTest
   module ::Blog
     class PostsController < ActionController::Base

actionpack/test/fixtures/routes/bogus.rb

@@ -0,0 +1 @@
+wrong :route

actionpack/test/fixtures/routes/external.rb

@@ -0,0 +1 @@
+get '/external' => 'external#index'