Update .init! to attempt repair if instructed

lib/vagrant/bundler.rb

@@ -31,7 +31,7 @@ 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)
+    def init!(plugins, repair=false)
       # Add HashiCorp RubyGems source
       Gem.sources << HASHICORP_GEMSTORE
 
@@ -48,7 +48,8 @@ module Vagrant
       # Sets that we can resolve our dependencies from
       current_set = Gem::Resolver::CurrentSet.new
       plugin_set = Gem::Resolver::VendorSet.new
-
+      repair_result = nil
+      begin
         # Register all known plugin specifications to the plugin set
         Dir.glob(plugin_gem_path.join('specifications/*.gemspec').to_s).each do |spec_path|
           spec = Gem::Specification.load(spec_path)
@@ -66,6 +67,23 @@ module Vagrant
 
         # Resolve the request set to ensure proper activation order
         solution = request_set.resolve(composed_set)
+      rescue Gem::UnsatisfiableDependencyError => failure
+        if repair
+          raise failure if @init_retried
+          install(plugins)
+          @init_retried = true
+          retry
+        else
+          $stderr.puts "Vagrant failed to properly initialize due to an error while"
+          $stderr.puts "while attempting to load configured plugins. This can be caused"
+          $stderr.puts "by manually tampering with the 'plugins.json' file, or by a"
+          $stderr.puts "recent Vagrant upgrade. To fix this problem, please run:\n\n"
+          $stderr.puts "    vagrant plugin repair\n\n"
+          $stderr.puts "The error message is shown below:\n\n"
+          $stderr.puts failure.message
+          exit 1
+        end
+      end
 
       # Activate the gems
       begin