Merge pull request #10861 from chef/lcg/lazy-attributes

Signed-off-by: Tim Smith <tsmith@chef.io>

6 files changed, 123 insertions, 9 deletions

diff --git a/chef-utils/lib/chef-utils/mash.rb b/chef-utils/lib/chef-utils/mash.rb
index 484e172b33..bb48064aa3 100644
--- a/chef-utils/lib/chef-utils/mash.rb
+++ b/chef-utils/lib/chef-utils/mash.rb
@@ -94,6 +94,10 @@ module ChefUtils
       end
     end
 
+    unless method_defined?(:regular_reader)
+      alias_method :regular_reader, :[]
+    end
+
     unless method_defined?(:regular_writer)
       alias_method :regular_writer, :[]=
     end
@@ -102,6 +106,11 @@ module ChefUtils
       alias_method :regular_update, :update
     end
 
+    # @param key<Object> The key to get.
+    def [](key)
+      regular_reader(key)
+    end
+
     # @param key<Object> The key to set.
     # @param value<Object>
     #   The value to set the key to.
@@ -114,6 +123,12 @@ module ChefUtils
 
     # internal API for use by Chef's deep merge cache
     # @api private
+    def internal_get(key)
+      regular_reader(key)
+    end
+
+    # internal API for use by Chef's deep merge cache
+    # @api private
     def internal_set(key, value)
       regular_writer(key, convert_value(value))
     end
diff --git a/lib/chef/delayed_evaluator.rb b/lib/chef/delayed_evaluator.rb
index df734c8303..f200f88410 100644
--- a/lib/chef/delayed_evaluator.rb
+++ b/lib/chef/delayed_evaluator.rb
@@ -17,5 +17,9 @@
 
 class Chef
   class DelayedEvaluator < Proc
+    def dup
+      # super returns a "Proc" (which seems buggy) so re-wrap it
+      self.class.new(&super) # rubocop:disable Layout/SpaceAroundKeyword
+    end
   end
 end
diff --git a/lib/chef/node/attribute.rb b/lib/chef/node/attribute.rb
index 29b60a98d5..3383b3c7e5 100644
--- a/lib/chef/node/attribute.rb
+++ b/lib/chef/node/attribute.rb
@@ -596,7 +596,7 @@ class Chef
           merge_with.each do |key, merge_with_value|
             value =
               if merge_onto.key?(key)
-                deep_merge!(safe_dup(merge_onto[key]), merge_with_value)
+                deep_merge!(safe_dup(merge_onto.internal_get(key)), merge_with_value)
               else
                 merge_with_value
               end
@@ -632,7 +632,7 @@ class Chef
           merge_with.each do |key, merge_with_value|
             value =
               if merge_onto.key?(key)
-                hash_only_merge!(safe_dup(merge_onto[key]), merge_with_value)
+                hash_only_merge!(safe_dup(merge_onto.internal_get(key)), merge_with_value)
               else
                 merge_with_value
               end
diff --git a/lib/chef/node/immutable_collections.rb b/lib/chef/node/immutable_collections.rb
index 49dc0256b9..79b1983a05 100644
--- a/lib/chef/node/immutable_collections.rb
+++ b/lib/chef/node/immutable_collections.rb
@@ -19,6 +19,7 @@ require_relative "common_api"
 require_relative "mixin/state_tracking"
 require_relative "mixin/immutablize_array"
 require_relative "mixin/immutablize_hash"
+require_relative "../delayed_evaluator"
 
 class Chef
   class Node
@@ -109,6 +110,12 @@ class Chef
         key
       end
 
+      def [](*args)
+        value = super
+        value = value.call while value.is_a?(::Chef::DelayedEvaluator)
+        value
+      end
+
       prepend Chef::Node::Mixin::StateTracking
       prepend Chef::Node::Mixin::ImmutablizeArray
     end
@@ -187,6 +194,12 @@ class Chef
         e
       end
 
+      def [](*args)
+        value = super
+        value = value.call while value.is_a?(::Chef::DelayedEvaluator)
+        value
+      end
+
       prepend Chef::Node::Mixin::StateTracking
       prepend Chef::Node::Mixin::ImmutablizeHash
     end
diff --git a/lib/chef/node/mixin/deep_merge_cache.rb b/lib/chef/node/mixin/deep_merge_cache.rb
index e88e079895..8978d77ea0 100644
--- a/lib/chef/node/mixin/deep_merge_cache.rb
+++ b/lib/chef/node/mixin/deep_merge_cache.rb
@@ -15,6 +15,8 @@
 # limitations under the License.
 #
 
+require_relative "../../delayed_evaluator"
+
 class Chef
   class Node
     module Mixin
@@ -46,13 +48,15 @@ class Chef
         alias :reset :reset_cache
 
         def [](key)
-          if deep_merge_cache.key?(key.to_s)
-            # return the cache of the deep merged values by top-level key
-            deep_merge_cache[key.to_s]
-          else
-            # save all the work of computing node[key]
-            deep_merge_cache[key.to_s] = merged_attributes(key)
-          end
+          ret = if deep_merge_cache.key?(key.to_s)
+                  # return the cache of the deep merged values by top-level key
+                  deep_merge_cache[key.to_s]
+                else
+                  # save all the work of computing node[key]
+                  deep_merge_cache[key.to_s] = merged_attributes(key)
+                end
+          ret = ret.call while ret.is_a?(::Chef::DelayedEvaluator)
+          ret
         end
 
       end
diff --git a/spec/unit/node_spec.rb b/spec/unit/node_spec.rb
index ec7beb9a50..284a993f5c 100644
--- a/spec/unit/node_spec.rb
+++ b/spec/unit/node_spec.rb
@@ -1951,4 +1951,82 @@ describe Chef::Node do
       expect(node["foo"]["bar"]["test"]).to eql("right")
     end
   end
+
+  describe "lazy values" do
+    it "supports lazy values in attributes" do
+      node.instance_eval do
+        default["foo"]["bar"] = lazy { node["fizz"]["buzz"] }
+        default["fizz"]["buzz"] = "works"
+      end
+      expect(node["foo"]["bar"]).to eql("works")
+    end
+
+    it "lazy values maintain laziness" do
+      node.instance_eval do
+        default["foo"]["bar"] = lazy { node["fizz"]["buzz"] }
+        default["fizz"]["buzz"] = "works"
+      end
+      expect(node["foo"]["bar"]).to eql("works")
+      node.default["fizz"]["buzz"] = "still works"
+      expect(node["foo"]["bar"]).to eql("still works")
+    end
+
+    it "supports recursive lazy values in attributes" do
+      node.instance_eval do
+        default["cool"]["beans"] = lazy { node["foo"]["bar"] }
+        default["foo"]["bar"] = lazy { node["fizz"]["buzz"] }
+        default["fizz"]["buzz"] = "works"
+      end
+      expect(node["cool"]["beans"]).to eql("works")
+      node.default["fizz"]["buzz"] = "still works"
+      expect(node["cool"]["beans"]).to eql("still works")
+    end
+
+    it "supports top level lazy values in attributes" do
+      # due to the top level deep merge cache these are special cases
+      node.instance_eval do
+        default["cool"] = lazy { node["foo"] }
+        default["foo"] = lazy { node["fizz"] }
+        default["fizz"] = "works"
+      end
+      expect(node["cool"]).to eql("works")
+      node.default["fizz"] = "still works"
+      expect(node["cool"]).to eql("still works")
+    end
+
+    it "supports deep merged values in attributes" do
+      node.instance_eval do
+        override["bar"]["cool"] = lazy { node["bar"]["foo"] }
+        override["bar"]["foo"] = lazy { node["bar"]["fizz"] }
+        override["bar"]["fizz"] = "works"
+      end
+      expect(node["bar"]["cool"]).to eql("works")
+      node.override["bar"]["fizz"] = "still works"
+      expect(node["bar"]["cool"]).to eql("still works")
+    end
+
+    it "supports overridden deep merged values in attributes (deep_merge)" do
+      node.instance_eval do
+        role_override["bar"] = { "cool" => "bad", "foo" => "bad", "fizz" => "bad" }
+        force_override["bar"]["cool"] = lazy { node["bar"]["foo"] }
+        force_override["bar"]["foo"] = lazy { node["bar"]["fizz"] }
+        force_override["bar"]["fizz"] = "works"
+      end
+      expect(node["bar"]["cool"]).to eql("works")
+      node.force_override["bar"]["fizz"] = "still works"
+      expect(node["bar"]["cool"]).to eql("still works")
+    end
+
+    it "supports overridden deep merged values in attributes (hash_only_merge)" do
+      node.instance_eval do
+        default["bar"] = { "cool" => "bad", "foo" => "bad", "fizz" => "bad" }
+        override["bar"]["cool"] = lazy { node["bar"]["foo"] }
+        override["bar"]["foo"] = lazy { node["bar"]["fizz"] }
+        override["bar"]["fizz"] = "works"
+      end
+      expect(node["bar"]["cool"]).to eql("works")
+      node.override["bar"]["fizz"] = "still works"
+      expect(node["bar"]["cool"]).to eql("still works")
+    end
+  end
 end