core: load ".vagrantplugins" in root path [GH-3775]

CHANGELOG.md

@@ -12,6 +12,8 @@ IMPROVEMENTS:
 
   - core: `has_plugin?` function now takes a second argument which is a
       version constraint requirement. [GH-4650]
+  - core: ".vagrantplugins" file in the same file as your Vagrantfile
+      will be loaded for defining inline plugins. [GH-3775]
   - commands/plugin: Plugin list machine-readable output contains the plugin
       name as the target for versions and other info. [GH-4506]
   - guests/arch: Support predictable network interface naming. [GH-4468]

lib/vagrant/environment.rb

@@ -164,6 +164,15 @@ module Vagrant
         @local_data_path = Pathname.new(File.expand_path(opts[:local_data_path], @cwd))
       end
 
+      # If we have a root path, load the ".vagrantplugins" file.
+      if root_path
+        plugins_file = root_path.join(".vagrantplugins")
+        if plugins_file.file?
+          @logger.info("Loading plugins file: #{plugins_file}")
+          load plugins_file
+        end
+      end
+
       setup_local_data_path
 
       # Setup the default private key