nix develop: Support derivations with multiple outputs

src/nix/develop.cc

@@ -130,7 +130,9 @@ StorePath getDerivationEnvironment(ref<Store> store, const StorePath & drvPath)
     drvName += "-env";
     for (auto & output : drv.outputs)
         drv.env.erase(output.first);
+    drv.outputs = {{"out", DerivationOutput { .path = StorePath::dummy }}};
     drv.env["out"] = "";
+    drv.env["_outputs_saved"] = drv.env["outputs"];
     drv.env["outputs"] = "out";
     drv.inputSrcs.insert(std::move(getEnvShPath));
     Hash h = hashDerivationModulo(*store, drv, true);

src/nix/get-env.sh

@@ -1,9 +1,18 @@
 set -e
 if [ -e .attrs.sh ]; then source .attrs.sh; fi
+
+outputs=$_outputs_saved
+for __output in $_outputs_saved; do
+    declare "$__output"="$out"
+done
+unset _outputs_saved __output
+
 export IN_NIX_SHELL=impure
 export dontAddDisableDepTrack=1
+
 if [[ -n $stdenv ]]; then
     source $stdenv/setup
 fi
+
 export > $out
 set >> $out

tests/shell.nix

@@ -24,6 +24,7 @@ let pkgs = rec {
     VAR_FROM_NIX = "bar";
     TEST_inNixShell = if inNixShell then "true" else "false";
     inherit stdenv;
+    outputs = ["dev" "out"];
   };
 
   # Used by nix-shell -p