Allow passing attributes via files instead of environment variables

Closes #473.

tests/local.mk

@@ -11,7 +11,7 @@ nix_tests = \
   binary-patching.sh timeout.sh secure-drv-outputs.sh nix-channel.sh \
   multiple-outputs.sh import-derivation.sh fetchurl.sh optimise-store.sh \
   binary-cache.sh nix-profile.sh repair.sh dump-db.sh case-hack.sh \
-  check-reqs.sh
+  check-reqs.sh pass-as-file.sh
   # parallel.sh
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))

tests/pass-as-file.sh

@@ -0,0 +1,17 @@
+source common.sh
+
+clearStore
+
+outPath=$(nix-build --no-out-link -E "
+with import ./config.nix;
+
+mkDerivation {
+  name = \"pass-as-file\";
+  passAsFile = [ \"foo\" ];
+  foo = [ \"xyzzy\" ];
+  builder = builtins.toFile \"builder.sh\" ''
+    [ \"\$(cat \$foo)\" = xyzzy ]
+    touch \$out
+  '';
+}
+")