WIP: immutabilizing deep mergelcg/remove-knockout-merge

3 files changed, 20 insertions, 6 deletions

diff --git a/lib/chef/mixin/deep_merge.rb b/lib/chef/mixin/deep_merge.rb
index 3d4690bb57..825406a93e 100644
--- a/lib/chef/mixin/deep_merge.rb
+++ b/lib/chef/mixin/deep_merge.rb
@@ -105,11 +105,19 @@ class Chef
         # If there are two Hashes, recursively merge.
         if merge_onto.kind_of?(Hash) && merge_with.kind_of?(Hash)
           merge_with.each do |key, merge_with_value|
-            merge_onto[key] = if merge_onto.has_key?(key)
-                                hash_only_merge(merge_onto[key], merge_with_value)
-                              else
-                                merge_with_value
-                              end
+            value =
+              if merge_onto.has_key?(key)
+                hash_only_merge(merge_onto[key], merge_with_value)
+              else
+                merge_with_value
+              end
+
+            if merge_onto.respond_to?(:public_method_that_only_deep_merge_should_use)
+              # we can't call ImmutableMash#[]= because its immutable, but we need to mutate it to build it in-place
+              merge_onto.public_method_that_only_deep_merge_should_use(key, value)
+            else
+              merge_onto[key] = value
+            end
           end
           merge_onto
 
diff --git a/lib/chef/node/attribute.rb b/lib/chef/node/attribute.rb
index 6c41e230ee..3c48f653eb 100644
--- a/lib/chef/node/attribute.rb
+++ b/lib/chef/node/attribute.rb
@@ -545,7 +545,9 @@ class Chef
            safe_dup(component)
          end
 
-         components.inject(ImmutableMash.new) do |merged, component|
+         return nil if components.compact.empty?
+
+         components.inject(ImmutableMash.new({})) do |merged, component|
            Chef::Mixin::DeepMerge.hash_only_merge!(merged, component)
          end
        end
diff --git a/lib/chef/node/immutable_collections.rb b/lib/chef/node/immutable_collections.rb
index af04ef26d4..56b8fed3b7 100644
--- a/lib/chef/node/immutable_collections.rb
+++ b/lib/chef/node/immutable_collections.rb
@@ -155,6 +155,10 @@ class Chef
         end
       end
 
+      def public_method_that_only_deep_merge_should_use(key, value)
+        internal_set(key, immutablize(value))
+      end
+
       alias :attribute? :has_key?
 
       # Redefine all of the methods that mutate a Hash to raise an error when called.