1 files changed, 77 insertions, 0 deletions
diff --git a/lib/chef/mixin/lazy_module_include.rb b/lib/chef/mixin/lazy_module_include.rb
new file mode 100644
index 0000000000..34e1fce4f1
--- /dev/null
+++ b/lib/chef/mixin/lazy_module_include.rb
@@ -0,0 +1,77 @@
+#
+# Copyright:: Copyright 2011-2016, Chef Software Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+class Chef
+  module Mixin
+    # If you have:
+    #
+    # module A
+    #   extend LazyModuleInclude
+    # end
+    #
+    # module B
+    #   include A
+    # end
+    #
+    # module C
+    #   include B
+    # end
+    #
+    # module Monkeypatches
+    #   def monkey
+    #     puts "monkey!"
+    #   end
+    # end
+    #
+    # A.send(:include, Monkeypatches)
+    #
+    # Then B and C and any classes that they're included in will also get the #monkey method patched into them.
+    #
+    module LazyModuleInclude
+
+      # Most of the magick is in this hook which creates a closure over the parent class and then builds an
+      # "infector" module which infects all descendants and which is responsible for updating the list of
+      # descendants in the parent class.
+      def included(klass)
+        super
+        parent_klass = self
+        infector = Module.new do
+          define_method(:included) do |subklass|
+            super(subklass)
+            subklass.extend(infector)
+            parent_klass.descendants.push(subklass)
+          end
+        end
+        klass.extend(infector)
+        parent_klass.descendants.push(klass)
+      end
+
+      def descendants
+        @descendants ||= []
+      end
+
+      def include(*classes)
+        super
+        classes.each do |klass|
+          descendants.each do |descendant|
+            descendant.send(:include, klass)
+          end
+        end
+      end
+    end
+  end
+end