2 files changed, 10 insertions, 11 deletions
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 7c0404ca62..18cd205bad 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -11,7 +11,7 @@ module ActionDispatch
     class Mapper
       URL_OPTIONS = [:protocol, :subdomain, :domain, :host, :port]
 
-      class Constraints < Endpoint #:nodoc:
+      class Constraints < Routing::Endpoint #:nodoc:
         attr_reader :app, :constraints
 
         SERVE = ->(app, req) { app.serve req }
@@ -600,17 +600,20 @@ module ActionDispatch
         def mount(app, options = nil)
           if options
             path = options.delete(:at)
-          else
-            unless Hash === app
-              raise ArgumentError, "must be called with mount point"
-            end
-
+          elsif Hash === app
             options = app
             app, path = options.find { |k, _| k.respond_to?(:call) }
             options.delete(app) if app
           end
 
-          raise "A rack application must be specified" unless path
+          raise ArgumentError, "A rack application must be specified" unless app.respond_to?(:call)
+          raise ArgumentError, <<-MSG.strip_heredoc unless path
+            Must be called with mount point
+
+              mount SomeRackApp, at: "some_route"
+              or
+              mount(SomeRackApp => "some_route")
+          MSG
 
           rails_app = rails_app? app
           options[:as] ||= app_name(app, rails_app)
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index 5f54ea130b..c4228df925 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -371,10 +371,6 @@ module ActionDispatch
       end
 
       def eval_block(block)
-        if block.arity == 1
-          raise "You are using the old router DSL which has been removed in Rails 3.1. " <<
-            "Please check how to update your routes file at: http://www.engineyard.com/blog/2010/the-lowdown-on-routes-in-rails-3/"
-        end
         mapper = Mapper.new(self)
         if default_scope
           mapper.with_default_scope(default_scope, &block)