Configuration versions can finalize config after loading

This is useful so that it can take a look at the final loaded
configuration object and possibly make some tweaks to the configuration
object. The use case this was built for was so that config V1 can verify
that there is always at least a single VM defined as a sub-VM, the
"default" VM.

lib/vagrant/config/loader.rb

@@ -103,8 +103,8 @@ module Vagrant
           end
         end
 
-        @logger.debug("Configuration loaded successfully")
-        result
+        @logger.debug("Configuration loaded successfully, finalizing and returning")
+        current_config_klass.finalize(result)
       end
 
       protected

lib/vagrant/config/version_base.rb

@@ -16,6 +16,19 @@ module Vagrant
         raise NotImplementedError
       end
 
+      # This is called just before configuration loading is complete of
+      # a potentially completely-merged value to perform final touch-ups
+      # to the configuration, if required.
+      #
+      # This is an optional method to implement. The default implementation
+      # will simply return the same object.
+      #
+      # @param [Object] obj Final configuration object.
+      # @param [Object] Finalized configuration object.
+      def self.finalize(obj)
+        obj
+      end
+
       # Loads the configuration for the given proc and returns a configuration
       # object. The return value is treated as an opaque object, so it can be
       # anything you'd like. The return value is the object that is passed

test/unit/vagrant/config/loader_test.rb

@@ -11,7 +11,7 @@ describe Vagrant::Config::Loader do
   # This is just a dummy implementation of a configuraiton loader which
   # simply acts on hashes.
   let(:test_loader) do
-    Class.new do
+    Class.new(Vagrant::Config::VersionBase) do
       def self.init
         {}
       end
@@ -55,6 +55,26 @@ describe Vagrant::Config::Loader do
     config[:foo].should == "yep"
   end
 
+  it "should finalize the configuration" do
+    # Create the finalize method on our loader
+    def test_loader.finalize(obj)
+      obj[:finalized] = true
+      obj
+    end
+
+    # Basic configuration proc
+    proc = lambda do |config|
+      config[:foo] = "yep"
+    end
+
+    # Run the actual configuration and assert that we get the proper result
+    instance.load_order = [:proc]
+    instance.set(:proc, [[current_version, proc]])
+    config = instance.load
+    config[:foo].should == "yep"
+    config[:finalized].should == true
+  end
+
   it "should only run the same proc once" do
     count = 0
     proc = Proc.new do |config|