Instead of shelling out, use the RubyGems API to install plugins

This gets us an accurate name of the gem even if it is installed
from a file.

lib/vagrant/errors.rb

@@ -340,6 +340,10 @@ module Vagrant
       error_key(:plugin_gem_error)
     end
 
+    class PluginInstallBadEntryPoint < VagrantError
+      error_key(:plugin_install_bad_entry_point)
+    end
+
     class PluginLoadError < VagrantError
       status_code(81)
       error_key(:plugin_load_error)

plugins/commands/plugin/action/install_gem.rb

@@ -1,5 +1,5 @@
 require "rubygems"
-require "rubygems/gem_runner"
+require "rubygems/dependency_installer"
 
 require "log4r"
 
@@ -20,14 +20,43 @@ module VagrantPlugins
           # Install the gem
           env[:ui].info(I18n.t("vagrant.commands.plugin.installing",
                                :name => plugin_name))
-          env[:gem_helper].cli(["install", plugin_name, "--no-ri", "--no-rdoc"])
+          installed_gems = env[:gem_helper].with_environment do
+            installer = Gem::DependencyInstaller.new(:document => [])
+            installer.install(plugin_name)
+          end
+
+          # The plugin spec is the last installed gem since RubyGems
+          # currently always installed the requested gem last.
+          @logger.debug("Installed #{installed_gems.length} gems.")
+          plugin_spec = installed_gems.last
+
+          # Store the installed name so we can uninstall it if things go
+          # wrong.
+          @installed_plugin_name = plugin_spec.name
 
           # Mark that we installed the gem
-          env[:plugin_state_file].add_plugin(plugin_name)
+          @logger.info("Adding the plugin to the state file...")
+          env[:plugin_state_file].add_plugin(plugin_spec.name)
+
+          # Tell the user
+          env[:ui].success(I18n.t("vagrant.commands.plugin.installed",
+                                  :name => plugin_spec.name))
 
           # Continue
           @app.call(env)
         end
+
+        def recover(env)
+          # If any error happens, we uninstall it and remove it from
+          # the state file. We can only do this if we successfully installed
+          # the gem in the first place.
+          if @installed_plugin_name
+            new_env = env.dup
+            new_env.delete(:interrupted)
+            new_env[:plugin_name] = @installed_plugin_name
+            new_env[:action_runner].run(Action.action_uninstall, new_env)
+          end
+        end
       end
     end
   end

plugins/commands/plugin/command/install.rb

@@ -7,8 +7,16 @@ module VagrantPlugins
     module Command
       class Install < Base
         def execute
+          options = {}
+
           opts = OptionParser.new do |o|
             o.banner = "Usage: vagrant plugin install <name> [-h]"
+            o.separator ""
+
+            o.on("--entry-point NAME", String,
+                 "The name of the entry point file for loading the plugin.") do |entry_point|
+              options[:entry_point] = entry_point
+            end
           end
 
           # Parse the options
@@ -17,7 +25,10 @@ module VagrantPlugins
           raise Vagrant::Errors::CLIInvalidUsage, :help => opts.help.chomp if argv.length < 1
 
           # Install the gem
-          action(Action.action_install, :plugin_name => argv[0])
+          action(Action.action_install, {
+            :plugin_entry_point => options[:entry_point],
+            :plugin_name        => argv[0]
+          })
 
           # Success, exit status 0
           0

plugins/commands/plugin/gem_helper.rb

@@ -13,37 +13,6 @@ 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.
-        # The final "false" here tells RubyGems we're not a TTY, so don't
-        # ask us things.
-        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
-        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.
-        # We capture this to check whether it succeeded or not by
-        # checking the "exit_code"
-        raise Vagrant::Errors::PluginGemError,
-          :output => gem_ui.errs.string.chomp if e.exit_code != 0
-      ensure
-        # 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.

templates/locales/en.yml

@@ -170,6 +170,11 @@ en:
         manage Vagrant plugins. The output of the errors are shown below:
 
         %{output}
+      plugin_install_bad_entry_point: |-
+        Attempting to load the plugin '%{name}' failed, because
+        the entry point doesn't exist. The entry point attempted was
+        '%{entry_point}'. If this is not correct, please manually
+        specify an `--entry-point` when installing the plugin.
       plugin_load_error: |-
         The plugin "%{plugin}" could not be found. Please make sure that it is
         properly installed via `vagrant plugin`.
@@ -412,6 +417,8 @@ en:
       plugin:
         no_plugins: |-
           No plugins installed.
+        installed: |-
+          Installed the '%{name}' plugin!
         installing: |-
           Installing the '%{name}' plugin. This can take a few minutes...
         uninstalling: |-