From 7e048eddf55637b9e81d704f6b9f1fdeca98a5ea Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Thu, 8 Apr 2010 11:25:14 +0000
Subject: * Fix blackholing.  If evaluation fails due to an assertion failure, 
  then the blackhole has to be removed to ensure that repeated   evaluation of
 the same value gives an assertion failure again rather   than an "infinite
 recursion" error.

---
 src/libexpr/eval.cc | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 98b6b7bdd150..e72538e60874 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -681,8 +681,14 @@ bool EvalState::evalBool(Env & env, Expr e)
 void EvalState::forceValue(Value & v)
 {
     if (v.type == tThunk) {
-        //v.type = tBlackhole;
-        eval(*v.thunk.env, v.thunk.expr, v);
+        ValueType saved = v.type;
+        try {
+            v.type = tBlackhole;
+            eval(*v.thunk.env, v.thunk.expr, v);
+        } catch (Error & e) {
+            v.type = saved;
+            throw;
+        }
     }
     else if (v.type == tCopy) {
         forceValue(*v.val);
-- 
cgit 1.4.1