StackedProcRunner abstraction which will be used for VM customization (in addition to configuration)

lib/vagrant.rb

@@ -8,7 +8,7 @@ PROJECT_ROOT = File.join(libdir, '..') unless defined?(PROJECT_ROOT)
 end
 
 # The vagrant specific files which must be loaded prior to the rest
-%w{vagrant/util vagrant/actions/base vagrant/downloaders/base vagrant/actions/collection 
+%w{vagrant/util vagrant/stacked_proc_runner vagrant/actions/base vagrant/downloaders/base vagrant/actions/collection
   vagrant/actions/runner vagrant/config vagrant/provisioners/base vagrant/provisioners/chef}.each do |f|
   require File.expand_path(f, libdir)
 end

lib/vagrant/stacked_proc_runner.rb

@@ -0,0 +1,33 @@
+module Vagrant
+  # Represents the "stacked proc runner" behavior which is used a
+  # couple places within Vagrant. This allows procs to "stack" on
+  # each other, then all execute in a single action. An example of
+  # its uses can be seen in the {Config} class.
+  module StackedProcRunner
+    # Returns the proc stack. This should always be called as the
+    # accessor of the stack. The instance variable itself should _never_
+    # be used.
+    #
+    # @return [Array<Proc>]
+    def proc_stack
+      @_proc_stack ||= []
+    end
+
+    # Adds (pushes) a proc to the stack. The actual proc added here is
+    # not executed, but merely stored.
+    #
+    # @param [Proc] block
+    def push_proc(&block)
+      proc_stack << block
+    end
+
+    # Executes all the procs on the stack, passing in the given arguments.
+    # The stack is not cleared afterwords. It is up to the user of this
+    # mixin to clear the stack by calling `proc_stack.clear`.
+    def run_procs!(*args)
+      proc_stack.each do |proc|
+        proc.call(*args)
+      end
+    end
+  end
+end

test/vagrant/stacked_proc_runner_test.rb

@@ -0,0 +1,43 @@
+require File.join(File.dirname(__FILE__), '..', 'test_helper')
+
+class StackedProcRunnerTest < Test::Unit::TestCase
+  class TestClass
+    include Vagrant::StackedProcRunner
+  end
+
+  setup do
+    @instance = TestClass.new
+    @instance.proc_stack.clear
+  end
+
+  should "not run the procs right away" do
+    obj = mock("obj")
+    obj.expects(:foo).never
+    @instance.push_proc { |config| obj.foo }
+    @instance.push_proc { |config| obj.foo }
+    @instance.push_proc { |config| obj.foo }
+  end
+
+  should "run the blocks when run_procs! is ran" do
+    obj = mock("obj")
+    obj.expects(:foo).times(2)
+    @instance.push_proc { obj.foo }
+    @instance.push_proc { obj.foo }
+    @instance.run_procs!
+  end
+
+  should "run the blocks with the same arguments" do
+    passed_config = mock("config")
+    @instance.push_proc { |config| assert passed_config.equal?(config) }
+    @instance.push_proc { |config| assert passed_config.equal?(config) }
+    @instance.run_procs!(passed_config)
+  end
+
+  should "not clear the blocks after running" do
+    obj = mock("obj")
+    obj.expects(:foo).times(2)
+    @instance.push_proc { obj.foo }
+    @instance.run_procs!
+    @instance.run_procs!
+  end
+end