core: Within a Bundler env, don't manage Bundler

lib/vagrant/bundler.rb

@@ -18,6 +18,8 @@ module Vagrant
     end
 
     def initialize
+      @enabled  = !::Bundler::SharedHelpers.in_bundle?
+      @enabled  = true if ENV["VAGRANT_FORCE_BUNDLER"]
       @monitor  = Monitor.new
 
       @gem_home = ENV["GEM_HOME"]
@@ -37,6 +39,9 @@ module Vagrant
     # Initializes Bundler and the various gem paths so that we can begin
     # loading gems. This must only be called once.
     def init!(plugins)
+      # If we're not enabled, then we don't do anything.
+      return if !@enabled
+
       # Setup the Bundler configuration
       @configfile = File.open(Tempfile.new("vagrant").path + "1", "w+")
       @configfile.close
@@ -202,6 +207,8 @@ module Vagrant
     end
 
     def with_isolated_gem
+      raise Errors::BundlerDisabled if !@enabled
+
       # Remove bundler settings so that Bundler isn't loaded when building
       # native extensions because it causes all sorts of problems.
       old_rubyopt = ENV["RUBYOPT"]

lib/vagrant/errors.rb

@@ -164,6 +164,10 @@ module Vagrant
       error_key(:failed, "vagrant.actions.box.verify")
     end
 
+    class BundlerDisabled < VagrantError
+      error_key(:bundler_disabled)
+    end
+
     class BundlerError < VagrantError
       error_key(:bundler_error)
     end

lib/vagrant/pre-rubygems.rb

@@ -5,17 +5,11 @@
 if defined?(Bundler)
   require "bundler/shared_helpers"
   if Bundler::SharedHelpers.in_bundle?
-    if ENV["VAGRANT_FORCE_PLUGINS"]
-      puts "Vagrant appears to be running in a Bundler environment. Normally,"
-      puts "plugins would not be loaded, but VAGRANT_FORCE_PLUGINS is enabled,"
-      puts "so they will be."
-      puts
-    else
-      puts "Vagrant appears to be running in a Bundler environment. Plugins"
-      puts "will not be loaded and plugin commands are disabled."
-      puts
-      ENV["VAGRANT_NO_PLUGINS"] = "1"
-    end
+    puts "Vagrant appears to be running in a Bundler environment. Your "
+    puts "existing Gemfile will be used. Vagrant will not auto-load any plugins."
+    puts "You must load any plugins you want manually in a Vagrantfile. You can"
+    puts "force Vagrant to take over with VAGRANT_FORCE_BUNDLER."
+    puts
   end
 end
 

templates/locales/en.yml

@@ -269,6 +269,13 @@ en:
         The box '%{name}' is still stored on disk in the Vagrant 1.0.x
         format. This box must be upgraded in order to work properly with
         this version of Vagrant.
+      bundler_disabled: |-
+        Vagrant's built-in bundler management mechanism is disabled because
+        Vagrant is running in an external bundler environment. In these
+        cases, plugin management does not work with Vagrant. To install
+        plugins, use your own Gemfile. To load plugins, either put the
+        plugins in the `plugins` group in your Gemfile or manually require
+        them in a Vagrantfile.
       bundler_error: |-
         Bundler, the underlying system Vagrant uses to install plugins,
         reported an error. The error is shown below. These errors are usually

vagrant-spec.config.example.rb

@@ -1,5 +1,3 @@
-ENV["VAGRANT_FORCE_PLUGINS"] = "1"
-
 require_relative "test/acceptance/base"
 
 Vagrant::Spec::Acceptance.configure do |c|