A really basic "list" command

plugins/commands/plugin/action.rb

@@ -13,10 +13,19 @@ module VagrantPlugins
         end
       end
 
+      # This middleware sequence will list all installed plugins.
+      def self.action_list
+        Vagrant::Action::Builder.new.tap do |b|
+          b.use BundlerCheck
+          b.use ListPlugins
+        end
+      end
+
       # The autoload farm
       action_root = Pathname.new(File.expand_path("../action", __FILE__))
       autoload :BundlerCheck, action_root.join("bundler_check")
       autoload :InstallGem, action_root.join("install_gem")
+      autoload :ListPlugins, action_root.join("list_plugins")
     end
   end
 end

plugins/commands/plugin/action/list_plugins.rb

@@ -0,0 +1,25 @@
+require "rubygems"
+
+module VagrantPlugins
+  module CommandPlugin
+    module Action
+      class ListPlugins
+        def initialize(app, env)
+          @app = app
+        end
+
+        def call(env)
+          env[:gem_helper].with_environment do
+            specs = Gem::Specification.find_all
+
+            specs.each do |spec|
+              env[:ui].info spec.name
+            end
+          end
+
+          @app.call(env)
+        end
+      end
+    end
+  end
+end

plugins/commands/plugin/gem_helper.rb

@@ -13,6 +13,11 @@ module VagrantPlugins
         @logger   = Log4r::Logger.new("vagrant::plugins::plugincommand::gemhelper")
       end
 
+      # This executes the `gem` command with the given arguments. Under
+      # the covers this is actually using the RubyGems API directly,
+      # instead of shelling out, which allows for more fine-grained control.
+      #
+      # @param [Array<String>] argv The arguments to send to the `gem` command.
       def cli(argv)
         # Initialize the UI to use for RubyGems. This allows us to capture
         # the stdout/stderr without actually going to the real STDOUT/STDERR.
@@ -21,13 +26,11 @@ module VagrantPlugins
         gem_ui = Gem::StreamUI.new(StringIO.new, StringIO.new, StringIO.new, false)
 
         # Set the GEM_HOME so that it is installed into our local gems path
-        old_gem_home = ENV["GEM_HOME"]
-        ENV["GEM_HOME"] = @gem_home
-        @logger.debug("Set GEM_HOME to: #{ENV["GEM_HOME"]}")
-        @logger.info("Calling gem with argv: #{argv.inspect}")
-        Gem.clear_paths
-        Gem::DefaultUserInteraction.use_ui(gem_ui) do
-          Gem::GemRunner.new.run(argv)
+        with_environment do
+          @logger.info("Calling gem with argv: #{argv.inspect}")
+          Gem::DefaultUserInteraction.use_ui(gem_ui) do
+            Gem::GemRunner.new.run(argv)
+          end
         end
       rescue Gem::SystemExitException => e
         # This means that something forced an exit within RubyGems.
@@ -36,13 +39,27 @@ module VagrantPlugins
         raise Vagrant::Errors::PluginGemError,
           :output => gem_ui.errs.string.chomp if e.exit_code != 0
       ensure
-        # Restore the old GEM_HOME
-        ENV["GEM_HOME"] = old_gem_home
-
         # Log the output properly
         @logger.debug("Gem STDOUT: #{gem_ui.outs.string}")
         @logger.debug("Gem STDERR: #{gem_ui.errs.string}")
       end
+
+      # This will yield the given block with the proper ENV setup so
+      # that RubyGems only sees the gems in the Vagrant-managed gem
+      # path.
+      def with_environment
+        old_gem_home = ENV["GEM_HOME"]
+        ENV["GEM_HOME"] = @gem_home
+        @logger.debug("Set GEM_HOME to: #{ENV["GEM_HOME"]}")
+
+        # Clear paths so that it reads the new GEM_HOME setting
+        Gem.clear_paths
+
+        yield
+      ensure
+        # Restore the old GEM_HOME
+        ENV["GEM_HOME"] = old_gem_home
+      end
     end
   end
 end