Add a more interesting test

In this one, we don't just output an existing derivation as is, but
modify it first.

tests/dyn-drv/recursive-mod-json.nix

@@ -0,0 +1,33 @@
+with import ./config.nix;
+
+let innerName = "foo"; in
+
+mkDerivation rec {
+  name = "${innerName}.drv";
+  SHELL = shell;
+
+  requiredSystemFeatures = [ "recursive-nix" ];
+
+  drv = builtins.unsafeDiscardOutputDependency (import ./text-hashed-output.nix).root.drvPath;
+
+  buildCommand = ''
+    export NIX_CONFIG='experimental-features = nix-command ca-derivations'
+
+    PATH=${builtins.getEnv "EXTRA_PATH"}:$PATH
+
+    # JSON of pre-existing drv
+    nix derivation show $drv | jq .[] > drv0.json
+
+    # Fix name
+    jq < drv0.json '.name = "${innerName}"' > drv1.json
+
+    # Extend `buildCommand`
+    jq < drv1.json '.env.buildCommand += "echo \"I am alive!\" >> $out/hello\n"' > drv0.json
+
+    # Used as our output
+    cp $(nix derivation add < drv0.json) $out
+  '';
+  __contentAddressed = true;
+  outputHashMode = "text";
+  outputHashAlgo = "sha256";
+}

tests/dyn-drv/recursive-mod-json.sh

@@ -0,0 +1,25 @@
+source common.sh
+
+# FIXME
+if [[ $(uname) != Linux ]]; then skipTest "Not running Linux"; fi
+
+enableFeatures 'recursive-nix'
+restartDaemon
+
+clearStore
+
+rm -f $TEST_ROOT/result
+
+EXTRA_PATH=$(dirname $(type -p nix)):$(dirname $(type -p jq))
+export EXTRA_PATH
+
+# Will produce a drv
+metaDrv=$(nix-instantiate ./recursive-mod-json.nix)
+
+# computed "dynamic" derivation
+drv=$(nix-store -r $metaDrv)
+
+# build that dyn drv
+res=$(nix-store -r $drv)
+
+grep 'I am alive!' $res/hello

tests/local.mk

@@ -111,6 +111,7 @@ nix_tests = \
   import-derivation.sh \
   ca/import-derivation.sh \
   dyn-drv/text-hashed-output.sh \
+  dyn-drv/recursive-mod-json.sh \
   nix_path.sh \
   case-hack.sh \
   placeholders.sh \

tests/recursive.sh

@@ -1,11 +1,11 @@
 source common.sh
 
-sed -i 's/experimental-features .*/& recursive-nix/' "$NIX_CONF_DIR"/nix.conf
-restartDaemon
-
 # FIXME
 if [[ $(uname) != Linux ]]; then skipTest "Not running Linux"; fi
 
+enableFeatures 'recursive-nix'
+restartDaemon
+
 clearStore
 
 rm -f $TEST_ROOT/result