Hi,

fs.promises is undefined on some platforms (at least on NixOS). I wasn't able to track down exact problem, but it seems that webpack is doing some magic with fs.
And I think we shouldn't use APIs which are flagged as experimental in Node.js LTS version (like fs.promises) because they can (indirectly) cause problems.

I suggest to replace

const stat = util.promisify(fs.stat);
...
return stat(this.crateDirectory).then(stats => {

I'll create PR.

Platform details:

• node v10.15.3
• npm 6.4.1
• yarn 1.13.0
• nixos 19.03