Have a base class to invoke actions on the plugins

plugins/commands/plugin/command/base.rb

@@ -0,0 +1,22 @@
+module VagrantPlugins
+  module CommandPlugin
+    module Command
+      class Base < Vagrant.plugin("2", :command)
+        # This is a helper for executing an action sequence with the proper
+        # environment hash setup so that the plugin specific helpers are
+        # in.
+        #
+        # @param [Object] callable the Middleware callable
+        # @param [Hash] env Extra environment hash that is merged in.
+        def action(callable, env=nil)
+          env = {
+            :gem_helper => GemHelper.new(@env.gems_path),
+            :plugin_state_file => StateFile.new(@env.data_dir.join("plugins.json"))
+          }.merge(env || {})
+
+          @env.action_runner.run(callable, env)
+        end
+      end
+    end
+  end
+end

plugins/commands/plugin/command/install.rb

@@ -1,9 +1,11 @@
 require 'optparse'
 
+require_relative "base"
+
 module VagrantPlugins
   module CommandPlugin
     module Command
-      class Install < Vagrant.plugin("2", :command)
+      class Install < Base
         def execute
           opts = OptionParser.new do |o|
             o.banner = "Usage: vagrant plugin install <name> [-h]"
@@ -15,11 +17,7 @@ module VagrantPlugins
           raise Vagrant::Errors::CLIInvalidUsage, :help => opts.help.chomp if argv.length < 1
 
           # Install the gem
-          @env.action_runner.run(Action.action_install, {
+          action(Action.action_install, :plugin_name => argv[0])
-            :gem_helper => GemHelper.new(@env.gems_path),
-            :plugin_name => argv[0],
-            :plugin_state_file => StateFile.new(@env.data_dir.join("plugins.json"))
-          })
 
           # Success, exit status 0
           0

plugins/commands/plugin/command/list.rb

@@ -0,0 +1,28 @@
+require 'optparse'
+
+require_relative "base"
+
+module VagrantPlugins
+  module CommandPlugin
+    module Command
+      class List < Base
+        def execute
+          opts = OptionParser.new do |o|
+            o.banner = "Usage: vagrant plugin list [-h]"
+          end
+
+          # Parse the options
+          argv = parse_options(opts)
+          return if !argv
+          raise Vagrant::Errors::CLIInvalidUsage, :help => opts.help.chomp if argv.length > 0
+
+          # List the installed plugins
+          action(Action.action_list)
+
+          # Success, exit status 0
+          0
+        end
+      end
+    end
+  end
+end

plugins/commands/plugin/command/root.rb

@@ -14,6 +14,11 @@ module VagrantPlugins
             require_relative "install"
             Install
           end
+
+          @subcommands.register(:list) do
+            require_relative "list"
+            List
+          end
         end
 
         def execute