Ensure the constraints block is only applied to the correct route

addresses issue #1907 - any routes that follow a route with a constraints
  block are inheriting the previous route's constraints.

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -190,13 +190,12 @@ module ActionDispatch
           end
 
           def blocks
-            block = @scope[:blocks] || []
-
-            if @options[:constraints].present? && !@options[:constraints].is_a?(Hash)
-              block << @options[:constraints]
+            constraints = @options[:constraints]
+            if constraints.present? && !constraints.is_a?(Hash)
+              [constraints]
+            else
+              @scope[:blocks] || []
             end
-
-            block
           end
 
           def constraints

actionpack/test/dispatch/routing_test.rb

@@ -504,6 +504,12 @@ class TestRoutingMapper < ActionDispatch::IntegrationTest
       match '/countries/:country/(*other)', :to => redirect{ |params, req| params[:other] ? "/countries/all/#{params[:other]}" : '/countries/all' }
 
       match '/:locale/*file.:format', :to => 'files#show', :file => /path\/to\/existing\/file/
+
+      scope '/italians' do
+        match '/writers', :to => 'italians#writers', :constraints => ::TestRoutingMapper::IpRestrictor
+        match '/sculptors', :to => 'italians#sculptors'
+        match '/painters/:painter', :to => 'italians#painters', :constraints => {:painter => /michelangelo/}
+      end
     end
   end
 
@@ -2229,6 +2235,20 @@ class TestRoutingMapper < ActionDispatch::IntegrationTest
     verify_redirect 'http://www.example.com/countries/all/cities'
   end
 
+  def test_constraints_block_not_carried_to_following_routes
+    get '/italians/writers'
+    assert_equal 'Not Found', @response.body
+
+    get '/italians/sculptors'
+    assert_equal 'italians#sculptors', @response.body
+
+    get '/italians/painters/botticelli'
+    assert_equal 'Not Found', @response.body
+
+    get '/italians/painters/michelangelo'
+    assert_equal 'italians#painters', @response.body
+  end
+
   def test_custom_resource_actions_defined_using_string
     get '/customers/inactive'
     assert_equal 'customers#inactive', @response.body