From daa8f85fcd3d5d7c48a51305818e05bee866b936 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Tue, 17 Oct 2006 14:13:15 +0000
Subject: [PATCH] * Backwards compatibility hack for user environments made by
 Nix <= 0.10.

---
 src/libexpr/get-drvs.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index acdc0c7b58..3c7061fcd3 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -10,6 +10,13 @@ string DrvInfo::queryDrvPath(EvalState & state) const
 {
     if (drvPath == "") {
         Expr a = attrs->get(toATerm("drvPath"));
+
+        /* Backwards compatibility hack with user environments made by
+           Nix <= 0.10: these contain illegal Path("") expressions. */
+        ATerm t;
+        if (a && matchPath(evalExpr(state, a), t))
+            return aterm2String(t);
+        
         PathSet context;
         (string &) drvPath = a ? coerceToPath(state, a, context) : "";
     }