Registries support merging

lib/vagrant/registry.rb

@@ -42,6 +42,22 @@ module Vagrant
       end
     end
 
+    # Merge one registry with another and return a completely new
+    # registry. Note that the result cache is completely busted, so
+    # any gets on the new registry will result in a cache miss.
+    def merge(other)
+      self.class.new.tap do |result|
+        result.merge!(self)
+        result.merge!(other)
+      end
+    end
+
+    # Like #{merge} but merges into self.
+    def merge!(other)
+      @items.merge!(other.__internal_state[:items])
+      self
+    end
+
     # Converts this registry to a hash
     def to_hash
       result = {}
@@ -51,5 +67,12 @@ module Vagrant
 
       result
     end
+
+    def __internal_state
+      {
+        :items => @items,
+        :results_cache => @results_cache
+      }
+    end
   end
 end

test/unit/vagrant/registry_test.rb

@@ -82,4 +82,47 @@ describe Vagrant::Registry do
     result["foo"].should == "foovalue"
     result["bar"].should == "barvalue"
   end
+
+  describe "merging" do
+    it "should merge in another registry" do
+      one = described_class.new
+      two = described_class.new
+
+      one.register("foo") { raise "BOOM!" }
+      two.register("bar") { raise "BAM!" }
+
+      three = one.merge(two)
+      expect { three["foo"] }.to raise_error("BOOM!")
+      expect { three["bar"] }.to raise_error("BAM!")
+    end
+
+    it "should NOT merge in the cache" do
+      one = described_class.new
+      two = described_class.new
+
+      one.register("foo") { [] }
+      one["foo"] << 1
+
+      two.register("bar") { [] }
+      two["bar"] << 2
+
+      three = one.merge(two)
+      three["foo"].should == []
+      three["bar"].should == []
+    end
+  end
+
+  describe "merge!" do
+    it "should merge into self" do
+      one = described_class.new
+      two = described_class.new
+
+      one.register("foo") { "foo" }
+      two.register("bar") { "bar" }
+
+      one.merge!(two)
+      one["foo"].should == "foo"
+      one["bar"].should == "bar"
+    end
+  end
 end