From 3550a32b25068aa8b1670ef7fd2af2b821f35dc1 Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Fri, 8 Jan 2021 22:09:35 +0100
Subject: [PATCH] primops/derivation: use position of currently evaluated
 attribute

* The position of the `name`-attribute appears in the trace.
* If e.g. `meta` has no `outPath`-attribute, a `cannot coerce set to
  string` error will be thrown where `pos` points to `name =` which is
  highly misleading.
---
 src/libexpr/primops.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 428adf4c2..f9eefddd0 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -953,7 +953,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
                     }
 
                 } else {
-                    auto s = state.coerceToString(posDrvName, *i->value, context, true);
+                    auto s = state.coerceToString(*i->pos, *i->value, context, true);
                     drv.env.emplace(key, s);
                     if (i->name == state.sBuilder) drv.builder = s;
                     else if (i->name == state.sSystem) drv.platform = s;