From a520b1cbc3327dfb8e3c6f503dfd0bd41e0a6d55 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Fri, 2 Apr 2004 10:49:37 +0000
Subject: [PATCH] * Print a more useful error message in case of an invalid
 derivation   binding.

---
 src/libexpr/primops.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 5aefa5b411..835a3217f3 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -181,7 +181,12 @@ Expr primDerivation(EvalState & state, Expr args)
         startNest(nest, lvlVomit, format("processing attribute `%1%'") % key);
 
         Strings ss;
-        processBinding(state, value, ne, ss);
+        try {
+            processBinding(state, value, ne, ss);
+        } catch (Error & e) {
+            throw Error(format("while processing derivation binding `%1%': %2%")
+                % key % e.msg());
+        }
 
         /* The `args' attribute is special: it supplies the
            command-line arguments to the builder. */