Make mergeable default behaviour and make flatten the explicit behavior

lib/vagrant/action/builder.rb

@@ -34,8 +34,10 @@ module Vagrant
       # Returns a mergeable version of the builder. If `use` is called with
       # the return value of this method, then the stack will merge, instead
       # of being treated as a separate single middleware.
-      def mergeable
-        [:merge, self]
+      def flatten
+        lambda do |env|
+          self.call(env)
+        end
       end
 
       # Adds a middleware class to the middleware stack. Any additional
@@ -44,9 +46,9 @@ module Vagrant
       #
       # @param [Class] middleware The middleware class
       def use(middleware, *args, &block)
-        if middleware.kind_of?(Array) && middleware[0] == :merge
+        if middleware.kind_of?(Builder)
           # Merge in the other builder's stack into our own
-          self.stack.concat(middleware[1].stack)
+          self.stack.concat(middleware.stack)
         else
           self.stack << [middleware, args, block]
         end

lib/vagrant/action/builtin.rb

@@ -28,8 +28,8 @@ module Vagrant
 
       # reload - Halts then restarts the VM
       reload = Builder.new do
-        use Action[:halt].mergeable
-        use Action[:start].mergeable
+        use Action[:halt]
+        use Action[:start]
       end
 
       register :reload, reload
@@ -40,14 +40,14 @@ module Vagrant
         use VM::Persist
         use VM::MatchMACAddress
         use VM::CheckGuestAdditions
-        use Action[:start].mergeable
+        use Action[:start]
       end
 
       register :up, up
 
       # destroy - Halts, cleans up, and destroys an existing VM
       destroy = Builder.new do
-        use Action[:halt].mergeable
+        use Action[:halt]
         use VM::DestroyUnusedNetworkInterfaces
         use VM::Destroy
       end

test/vagrant/action/builder_test.rb

@@ -40,26 +40,22 @@ class ActionBuilderTest < Test::Unit::TestCase
           use 3
         end
 
-        @instance.use 1
-        @instance.use other.mergeable
-        assert_equal 3, @instance.stack.length
-      end
-
-      should "not merge in another builder if not mergeable" do
-        other = @klass.new do
-          use 2
-          use 3
-        end
-
         @instance.use 1
         @instance.use other
-        assert_equal 2, @instance.stack.length
+        assert_equal 3, @instance.stack.length
       end
     end
 
-    context "mergeable" do
-      should "return the merge format with the builder" do
-        assert_equal [:merge, @instance], @instance.mergeable
+    context "flatten" do
+      should "return the flattened format of the builder" do
+        env = Vagrant::Action::Environment.new(nil)
+        env.expects(:foo).once
+
+        func = lambda { |x| x.foo }
+        @instance.use func
+        proc = @instance.flatten
+        assert proc.respond_to?(:call)
+        proc.call(env)
       end
     end