core: ask what provider to use if multiple providers

lib/vagrant/action/builtin/box_add.rb

@@ -101,6 +101,28 @@ module Vagrant
             # provider.
             metadata_provider = metadata_version.provider(
               metadata_version.providers.first)
+          else
+            providers = metadata_version.providers.sort
+
+            choice = 0
+            options = providers.map do |p|
+              choice += 1
+              "#{choice}) #{p}"
+            end.join("\n")
+
+            # We have more than one provider, ask the user what they want
+            choice = env[:ui].ask(I18n.t(
+              "vagrant.box_add_choose_provider",
+              options: options))
+            choice = choice.to_i if choice
+            while !choice || choice <= 0 || choice > providers.length
+              choice = env[:ui].ask(I18n.t(
+                "vagrant.box_add_choose_provider_again"))
+              choice = choice.to_i if choice
+            end
+
+            metadata_provider = metadata_version.provider(
+              providers[choice-1])
           end
 
           box_add(
@@ -331,7 +353,6 @@ module Vagrant
             end
           end
 
-          # TODO: do the HEAD request
           output = d.head
           match  = output.scan(/^Content-Type: (.+?)$/).last
           return false if !match

templates/locales/en.yml

@@ -4,6 +4,16 @@ en:
       Machine booted and ready!
     boot_waiting: |-
       Waiting for machine to boot. This may take a few minutes...
+    box_add_choose_provider: |-
+      This box can work with multiple providers! The providers that it
+      can work with are listed below. Please review the list and choose
+      the provider you will be working with.
+
+      %{options}
+
+      Enter your choice:
+    box_add_choose_provider_again: |-
+      Invalid choice. Try again:
     box_add_with_version: |-
       Adding box '%{name}' (v%{version}) for '%{provider}' provider...
     box_added: |-

test/unit/vagrant/action/builtin/box_add_test.rb

@@ -450,6 +450,51 @@ describe Vagrant::Action::Builtin::BoxAdd do
       expect(env[:box_added]).to equal(box)
     end
 
+    it "asks the user what provider if multiple options" do
+      box_path = iso_env.box2_file(:virtualbox)
+      tf = Tempfile.new("vagrant").tap do |f|
+        f.write(<<-RAW)
+        {
+          "name": "foo/bar",
+          "versions": [
+            {
+              "version": "0.5"
+            },
+            {
+              "version": "0.7",
+              "providers": [
+                {
+                  "name": "virtualbox",
+                  "url":  "#{box_path}"
+                },
+                {
+                  "name": "vmware",
+                  "url":  "#{iso_env.box2_file(:vmware)}"
+                }
+              ]
+            }
+          ]
+        }
+        RAW
+        f.close
+      end
+
+      env[:box_url] = tf.path
+
+      env[:ui].should_receive(:ask).and_return("1")
+
+      box_collection.should_receive(:add).with do |path, name, version|
+        expect(checksum(path)).to eq(checksum(box_path))
+        expect(name).to eq("foo/bar")
+        expect(version).to eq("0.7")
+        true
+      end.and_return(box)
+
+      app.should_receive(:call).with(env)
+
+      subject.call(env)
+    end
+
     it "raises an exception if no matching version" do
       box_path = iso_env.box2_file(:vmware)
       tf = Tempfile.new("vagrant").tap do |f|