core: errors can use error_message to specify string error message

lib/vagrant/errors.rb

@@ -48,6 +48,10 @@ module Vagrant
         error_namespace(namespace) if namespace
       end
 
+      def self.error_message(message)
+        define_method(:error_message) { message }
+      end
+
       def self.error_namespace(namespace)
         define_method(:error_namespace) { namespace }
       end
@@ -55,11 +59,20 @@ module Vagrant
       def initialize(message=nil, *args)
         message = { :_key => message } if message && !message.is_a?(Hash)
         message = { :_key => error_key, :_namespace => error_namespace }.merge(message || {})
-        message = translate_error(message)
+
+        if error_key
+          message = translate_error(message)
+        else
+          message = error_message
+        end
 
         super
       end
 
+      # The error message for this error. This is used if no error_key
+      # is specified for a translatable error message.
+      def error_message; "No error message"; end
+
       # The default error namespace which is used for the error key.
       # This can be overridden here or by calling the "error_namespace"
       # class method.

templates/locales/en.yml

@@ -572,6 +572,7 @@ en:
         Port: %{port}
         Username: %{username}
         Private key: %{key_path}
+      test_key: "test value"
       ui_expects_tty: |-
         Vagrant is attempting to interface with the UI in a way that requires
         a TTY. Most actions in Vagrant that require a TTY have configuration

test/unit/vagrant/errors_test.rb

@@ -0,0 +1,33 @@
+require File.expand_path("../../base", __FILE__)
+
+describe Vagrant::Errors::VagrantError do
+  describe "subclass with error key" do
+    let(:klass) do
+      Class.new(described_class) do
+        error_key("test_key")
+      end
+    end
+
+    subject { klass.new }
+
+    it "should use the translation for the message" do
+      subject.to_s.should == "test value"
+    end
+
+    its("status_code") { should eq(1) }
+  end
+
+  describe "subclass with error message" do
+    let(:klass) do
+      Class.new(described_class) do
+        error_message("foo")
+      end
+    end
+
+    subject { klass.new }
+
+    it "should use the translation for the message" do
+      subject.to_s.should == "foo"
+    end
+  end
+end