node updater improvements

- Make it run from anywhere
- overwrite old packages only on success to prevent getting into a bad
state

pkgs/development/node-packages/generate.sh

@@ -1,10 +1,15 @@
 #!/usr/bin/env nix-shell
-#! nix-shell -I nixpkgs=../../.. -i bash -p nodePackages.node2nix
-# NOTE: Script must be run from the node-packages directory
-
+#! nix-shell shell-generate.nix -i bash
 set -eu -o pipefail
 
-rm -f node-env.nix
-node2nix --nodejs-10 -i node-packages-v10.json -o node-packages-v10.nix -c composition-v10.nix
-node2nix --nodejs-12 -i node-packages-v12.json -o node-packages-v12.nix -c composition-v12.nix
-node2nix --nodejs-13 -i node-packages-v13.json -o node-packages-v13.nix -c composition-v13.nix
+cd "$NODE_NIXPKGS_PATH/pkgs/development/node-packages"
+rm -f ./node-env.nix
+for version in 10 12 13; do
+    tmpdir=$(mktemp -d)
+    node2nix --nodejs-$version -i node-packages-v$version.json -o $tmpdir/node-packages-v$version.nix -c $tmpdir/composition-v$version.nix
+    if [ $? -eq 0 ]; then
+        mv $tmpdir/node-packages-v$version.nix .
+        mv $tmpdir/composition-v$version.nix .
+    fi
+done
+cd -

pkgs/development/node-packages/shell-generate.nix

@@ -0,0 +1,9 @@
+{ nixpkgs ? import ../../.. {} }:
+with nixpkgs;
+mkShell {
+  buildInputs = [
+    bash nodePackages.node2nix
+  ];
+  NODE_NIXPKGS_PATH = toString ./.;
+}
+