(6911) Add bookkeeping facade around Transaction#relationship_graph

To implement graph frontiers transactions need to track information about the
catalog's relationship graph.  For various reasons (serialzation, lifetime,
etc.) the data belongs with the transaction rather than the catalog or its
relationship graph.  This commit introduces a facade around the property used
to cheat Demeter which has the apropriate lifetime and can be used to hold the
state information durring a traversal.

Paired-with: Jesse Wolfe

1 files changed, 32 insertions, 1 deletions

diff --git a/lib/puppet/transaction.rb b/lib/puppet/transaction.rb
index ad79f176e..928a1b488 100644
--- a/lib/puppet/transaction.rb
+++ b/lib/puppet/transaction.rb
@@ -277,8 +277,39 @@ class Puppet::Transaction
     end
   end
 
+  # We want to monitor changes in the relationship graph of our
+  # catalog but this is complicated by the fact that the catalog
+  # both is_a graph and has_a graph, by the fact that changes to 
+  # the structure of the object can have adverse serialization
+  # effects, by threading issues, by order-of-initialization issues,
+  # etc.  
+  #
+  # Since the proper lifetime/scope of the monitoring is a transaction
+  # and the transaction is already commiting a mild law-of-demeter 
+  # transgression, we cut the Gordian knot here by simply wrapping the
+  # transaction's view of the resource graph to capture and maintain
+  # the information we need.  Nothing outside the transaction needs
+  # this information, and nothing outside the transaction can see it
+  # except via the Transaction#relationship_graph
+
+  class Relationship_graph_wrapper
+    def initialize(real_graph,transaction)
+      @real_graph = real_graph
+      @transaction = transaction
+    end
+    def method_missing(*args,&block)
+      @real_graph.send(*args,&block)
+    end
+    def add_vertex(v)
+      @real_graph.add_vertex(v)
+    end
+    def add_edge(f,t)
+      @real_graph.add_edge(f,t)
+    end
+  end
+
   def relationship_graph
-    catalog.relationship_graph
+    @relationship_graph ||= Relationship_graph_wrapper.new(catalog.relationship_graph,self)
   end
 
   def add_resource_status(status)