Make npm-postinstall.sh more robust

ci/build/npm-postinstall.sh

@@ -4,18 +4,34 @@ set -eu
 main() {
   cd lib/vscode
 
+  case "${npm_config_user_agent-}" in npm*)
+    # We are running under npm.
+    if [ "${npm_config_unsafe_perm-}" != "true" ]; then
+      echo "Please pass --unsafe-perm to npm to install code-server"
+      echo "Otherwise the postinstall script does not have permissions to run"
+      echo "See https://docs.npmjs.com/misc/config#unsafe-perm"
+      echo "See https://stackoverflow.com/questions/49084929/npm-sudo-global-installation-unsafe-perm"
+      exit 1
+    fi
+    ;;
+  esac
+
   # We have to rename node_modules.bundled to node_modules.
   # The bundled modules were renamed originally to avoid being ignored by yarn.
-  local node_modules
   node_modules="$(find . -depth -name "node_modules.bundled")"
-  local nm
   for nm in $node_modules; do
     rm -Rf "${nm%.bundled}"
     mv "$nm" "${nm%.bundled}"
   done
 
+  # $npm_config_global makes npm rebuild return without rebuilding.
+  unset npm_config_global
   # Rebuilds native modules.
-  npm rebuild
+  if ! npm rebuild; then
+    echo "You may not have the required dependencies to build the native modules."
+    echo "Please see https://github.com/cdr/code-server/blob/master/doc/npm.md"
+    exit 1
+  fi
 }
 
 main "$@"