Rewrite builtin derivation environment

Also add a test.

Fixes #1803.
Closes #1805.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 523d737d9b..55066205db 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2933,8 +2933,13 @@ void DerivationGoal::runChild()
         if (drv->isBuiltin()) {
             try {
                 logger = makeJSONLogger(*logger);
+
+                BasicDerivation drv2(*drv);
+                for (auto & e : drv2.env)
+                    e.second = rewriteStrings(e.second, inputRewrites);
+
                 if (drv->builder == "builtin:fetchurl")
-                    builtinFetchurl(*drv, netrcData);
+                    builtinFetchurl(drv2, netrcData);
                 else
                     throw Error(format("unsupported builtin function '%1%'") % string(drv->builder, 8));
                 _exit(0);