--provider on box add supports any format of that provider

CHANGELOG.md

@@ -18,6 +18,8 @@ IMPROVEMENTS:
   - Vagrant will show an error if VirtualBox 4.2.14 is running.
   - Added provider to BoxNotFound error message. [GH-1692]
   - If Ansible fails to run properly, show an error message. [GH-1699]
+  - Adding a box with the `--provider` flag will now allow a box for
+    any of that provider's supported formats.
 
 BUG FIXES:
 

lib/vagrant/action/builtin/box_add.rb

@@ -44,12 +44,23 @@ module Vagrant
             return
           end
 
+          box_formats = env[:box_provider]
+          if box_formats
+            # Determine the formats a box can support and allow the box to
+            # be any of those formats.
+            provider_plugin = Vagrant.plugin("2").manager.providers[env[:box_provider]]
+            if provider_plugin
+              box_formats = provider_plugin[1][:box_format]
+              box_formats ||= env[:box_provider]
+            end
+          end
+
           # Add the box
           env[:ui].info I18n.t("vagrant.actions.box.add.adding", :name => env[:box_name])
           added_box = nil
           begin
             added_box = env[:box_collection].add(
-              @temp_path, env[:box_name], env[:box_provider], env[:box_force])
+              @temp_path, env[:box_name], box_formats, env[:box_force])
           rescue Vagrant::Errors::BoxUpgradeRequired
             # Upgrade the box
             env[:box_collection].upgrade(env[:box_name])