core: config raises NoMethodError on bad calls once finalized

lib/vagrant/config/v2/root.rb

@@ -48,6 +48,7 @@ module Vagrant
 
           @keys.each do |_key, instance|
             instance.finalize!
+            instance._finalize!
           end
         end
 

lib/vagrant/plugin/v2/config.rb

@@ -70,6 +70,8 @@ module Vagrant
         # Capture all bad configuration calls and save them for an error
         # message later during validation.
         def method_missing(name, *args, &block)
+          return super if @__finalized
+
           name = name.to_s
           name = name[0...-1] if name.end_with?("=")
 
@@ -130,6 +132,11 @@ module Vagrant
           return [I18n.t("vagrant.config.common.bad_field",
                          :fields => @__invalid_methods.to_a.sort.join(", "))]
         end
+
+        # An internal finalize call that no subclass should override.
+        def _finalize!
+          @__finalized = true
+        end
       end
     end
   end

test/unit/vagrant/config/v2/root_test.rb

@@ -41,8 +41,8 @@ describe Vagrant::Config::V2::Root do
     }
   end
 
-  describe "finalization" do
-    it "should finalize un-used keys" do
+  describe "#finalize!" do
+    it "should call #finalize!" do
       foo_class = Class.new do
         attr_accessor :foo
 
@@ -57,6 +57,17 @@ describe Vagrant::Config::V2::Root do
 
       instance.foo.foo.should == "SET"
     end
+
+    it "should call #_finalize!" do
+      klass = Class.new
+
+      klass.any_instance.should_receive(:finalize!)
+      klass.any_instance.should_receive(:_finalize!)
+
+      map = { foo: klass }
+      instance = described_class.new(map)
+      instance.finalize!
+    end
   end
 
   describe "validation" do

test/unit/vagrant/plugin/v2/config_test.rb

@@ -12,7 +12,9 @@ describe Vagrant::Plugin::V2::Config do
 
   let(:unset_value) { described_class.const_get("UNSET_VALUE") }
 
-  describe "merging" do
+  subject { foo_class.new }
+
+  describe "#merge" do
     it "should merge by default by simply copying each instance variable" do
       one = foo_class.new
       one.one = 2
@@ -57,4 +59,18 @@ describe Vagrant::Plugin::V2::Config do
       result.instance_variable_get(:@__bar).should be_nil
     end
   end
+
+  describe "#method_missing" do
+    it "returns a DummyConfig object" do
+      expect(subject.i_should_not_exist).
+        to be_kind_of(Vagrant::Config::V2::DummyConfig)
+    end
+
+    it "raises an error if finalized (internally)" do
+      subject._finalize!
+
+      expect { subject.i_should_not_exist }.
+        to raise_error(NoMethodError)
+    end
+  end
 end