Raise an exception if a non-MachineState is returned

lib/vagrant/errors.rb

@@ -248,6 +248,10 @@ module Vagrant
       error_key(:machine_not_found)
     end
 
+    class MachineStateInvalid < VagrantError
+      error_key(:machine_state_invalid)
+    end
+
     class MultiVMEnvironmentRequired < VagrantError
       status_code(5)
       error_key(:multi_vm_required)

lib/vagrant/machine.rb

@@ -277,7 +277,9 @@ module Vagrant
     #
     # @return [Symbol]
     def state
-      @provider.state
+      result = @provider.state
+      raise Errors::MachineStateInvalid if !result.is_a?(MachineState)
+      result
     end
 
     protected

templates/locales/en.yml

@@ -145,6 +145,12 @@ en:
       machine_not_found: |-
         The machine with the name '%{name}' was not found configured for
         this Vagrant environment.
+      machine_state_invalid: |-
+        An internal error has occurred! The provider of the machine you're
+        trying to work with reported an invalid state. This is a bug with
+        the provider you're using, and not with Vagrant itself or with
+        any configuration you may have done. Please report this bug to
+        the proper location.
       multi_vm_required: |-
         A multi-vm environment is required for name specification to this command.
       multi_vm_target_required: |-

test/unit/vagrant/machine_test.rb

@@ -385,10 +385,16 @@ describe Vagrant::Machine do
 
   describe "state" do
     it "should query state from the provider" do
-      state = :running
+      state = Vagrant::MachineState.new(:id, "short", "long")
 
       provider.should_receive(:state).and_return(state)
-      instance.state.should == state
+      instance.state.id.should == :id
+    end
+
+    it "should raise an exception if a MachineState is not returned" do
+      provider.should_receive(:state).and_return(:old_school)
+      expect { instance.state }.
+        to raise_error(Vagrant::Errors::MachineStateInvalid)
     end
   end
 end