Add infrastructure for efficient walks through the `Edge` graph

Store a mark in each `Edge` to be updated as it is encountered by a walk.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/graph.h b/src/graph.h
index 9e82ca2..1b30dee 100644
--- a/src/graph.h
+++ b/src/graph.h
@@ -128,7 +128,13 @@ private:
 
 /// An edge in the dependency graph; links between Nodes using Rules.
 struct Edge {
-  Edge() : rule_(NULL), pool_(NULL), env_(NULL),
+  enum VisitMark {
+    VisitNone,
+    VisitInStack,
+    VisitDone
+  };
+
+  Edge() : rule_(NULL), pool_(NULL), env_(NULL), mark_(VisitNone),
            outputs_ready_(false), deps_missing_(false),
            implicit_deps_(0), order_only_deps_(0), implicit_outs_(0) {}
 
@@ -156,6 +162,7 @@ struct Edge {
   vector<Node*> inputs_;
   vector<Node*> outputs_;
   BindingEnv* env_;
+  VisitMark mark_;
   bool outputs_ready_;
   bool deps_missing_;