From eb7167d456b8ef2dad3846ca2ba6438b060518c9 Mon Sep 17 00:00:00 2001
From: Nico Weber <nicolasweber@gmx.de>
Date: Wed, 18 Mar 2015 16:54:16 -0400
Subject: [PATCH] Don't crash on cyclic references between rule bindings.

Fixes #902.

This dynamically detects cycles.  I like this approach less than
detecting them statically when parsing rules [1], but it has the
advantage that it doesn't break existing ninja manifest files.

It has the disadvantage that it slows down manifest_parser_perftest by
3.9%.

1: https://github.com/martine/ninja/commit/cc6f54d6d436047
---
 src/graph.cc | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/graph.cc b/src/graph.cc
index b19dc85..41055ec 100644
--- a/src/graph.cc
+++ b/src/graph.cc
@@ -226,6 +226,7 @@ struct EdgeEnv : public Env {
                       vector<Node*>::iterator end,
                       char sep);
 
+  vector<string> lookups_;
   Edge* edge_;
   EscapeKind escape_in_out_;
 };
@@ -243,8 +244,19 @@ string EdgeEnv::LookupVariable(const string& var) {
                         ' ');
   }
 
+  vector<string>::const_iterator it;
+  if ((it = find(lookups_.begin(), lookups_.end(), var)) != lookups_.end()) {
+    string cycle;
+    for (; it != lookups_.end(); ++it)
+      cycle.append(*it + " -> ");
+    cycle.append(var);
+    Fatal(("cycle in rule variables: " + cycle).c_str());
+  }
+
   // See notes on BindingEnv::LookupWithFallback.
   const EvalString* eval = edge_->rule_->GetBinding(var);
+  if (eval)
+    lookups_.push_back(var);
   return edge_->env_->LookupWithFallback(var, eval, this);
 }
 
-- 
2.7.4