Add a simple push plugin in Go

The only tweak required to get this to work was allowing a DummyConfig
to survive being passed through a remote plugin on the Ruby side.

builtin/myplugin/main.go

@@ -5,6 +5,7 @@ import (
 	"github.com/hashicorp/vagrant/builtin/myplugin/command"
 	communincator "github.com/hashicorp/vagrant/builtin/myplugin/communicator"
 	"github.com/hashicorp/vagrant/builtin/myplugin/host"
+	"github.com/hashicorp/vagrant/builtin/myplugin/push"
 )
 
 //go:generate protoc -I ../../.. --go_opt=plugins=grpc --go_out=../../.. vagrant-ruby/builtin/myplugin/proto/plugin.proto
@@ -16,6 +17,7 @@ var CommandOptions = []sdk.Option{
 		&command.Command{},
 		&host.AlwaysTrueHost{},
 		&communincator.DummyCommunicator{},
+		&push.Encouragement{},
 	),
 	sdk.WithMappers(StructToCommunincatorOptions),
 	sdk.WithName("myplugin"),

builtin/myplugin/push/encouragement.go

@@ -0,0 +1,23 @@
+package push
+
+import (
+	"github.com/hashicorp/vagrant-plugin-sdk/component"
+	"github.com/hashicorp/vagrant-plugin-sdk/core"
+	"github.com/hashicorp/vagrant-plugin-sdk/terminal"
+)
+
+// This is a push strategy that provides encouragement for the code you push
+type Encouragement struct{}
+
+func (e *Encouragement) PushFunc() interface{} {
+	return e.Push
+}
+
+func (e *Encouragement) Push(ui terminal.UI, proj core.Project) error {
+	ui.Output("You've invoked a push plugin written in Go! Great work!")
+	return nil
+}
+
+var (
+	_ component.Push = (*Encouragement)(nil)
+)

lib/vagrant/config/v2/dummy_config.rb

@@ -7,6 +7,14 @@ module Vagrant
         LOG  = Log4r::Logger.new("vagrant::config::v2::dummy_config")
 
         def method_missing(name, *args, &block)
+          # If a DummyConfig ends up as a last arg in a situation where it's
+          # being passed through a method with *kwargs, ruby 2.x will try to
+          # implicitly convert it into a hash. If it responds to to_hash but
+          # does not return an actual hash, Ruby gets mad.
+          if name == :to_hash
+            return super
+          end
+
           # Trying to define a variable
           if name.to_s.match(/^[\w]*=/)
             LOG.debug("found name #{name}")

test/unit/vagrant/config/v2/dummy_config_test.rb

@@ -21,4 +21,11 @@ describe Vagrant::Config::V2::DummyConfig do
     expect { subject[:foo] = :bar }.
       to_not raise_error
   end
+
+  it "should survive being the last arg to a method that captures kwargs without a ruby conversion error" do
+    arg_capturer = lambda { |*args, **kwargs| }
+    expect {
+      arg_capturer.call(subject)
+    }.to_not raise_error
+  end
 end