core: shorthand boxes must be foo/bar formatted, better errors

lib/vagrant/action/builtin/box_add.rb

@@ -37,10 +37,14 @@ module Vagrant
           # then expand it properly.
           expanded = false
           url.each_index do |i|
-            uri = URI.parse(url[i])
-            if !uri.scheme && !File.file?(url[i])
+            next if url[i] !~ /^[^\/]+\/[^\/]+$/
+
+            if !File.file?(url[i])
+              server   = Vagrant.server_url
+              raise Errors::BoxServerNotSet if !server
+
               expanded = true
-              url[i] = "#{Vagrant.server_url}/#{url[i]}"
+              url[i] = "#{server}/#{url[i]}"
             end
           end
 

lib/vagrant/errors.rb

@@ -204,6 +204,10 @@ module Vagrant
       error_key(:box_remove_multi_version)
     end
 
+    class BoxServerNotSet < VagrantError
+      error_key(:box_server_not_set)
+    end
+
     class BoxUnpackageFailure < VagrantError
       error_key(:untar_failure, "vagrant.actions.box.unpackage")
     end

templates/locales/en.yml

@@ -419,6 +419,17 @@ en:
         the provider specified. Please double-check and try again.
 
         The providers for this are: %{providers}
+      box_server_not_set: |-
+        A URL to a Vagrant Cloud server is not set, so boxes cannot
+        be added with a shorthand ("mitchellh/precise64") format.
+        You may also be seeing this error if you meant to type in
+        a path to a box file which doesn't exist locally on your
+        system.
+
+        To set a URL to a Vagrant Cloud server, set the
+        `VAGRANT_SERVER_URL` environmental variable. Or, if you
+        meant to use a file path, make sure the path to the file
+        is valid.
       box_update_multi_provider: |-
         You requested to update the box '%{name}'. This box has
         multiple providers. You must explicitly select a single

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

@@ -262,6 +262,21 @@ describe Vagrant::Action::Builtin::BoxAdd do
       end
     end
 
+    it "raises an error if no Vagrant server is set" do
+      tf = Tempfile.new("foo")
+      tf.close
+
+      env[:box_url] = "mitchellh/precise64.json"
+
+      box_collection.should_receive(:add).never
+      app.should_receive(:call).never
+
+      Vagrant.stub(server_url: nil)
+
+      expect { subject.call(env) }.
+        to raise_error(Vagrant::Errors::BoxServerNotSet)
+    end
+
     it "raises an error if shorthand is invalid" do
       tf = Tempfile.new("foo")
       tf.close