ExperimentalWarning: The fs.promises API is experimental (Node.js 10.1.0)

[bajtos]

• Operating System: MacOS 10.13.4
• Node.js version: 10.1.0
• fs-extra version: 5.0.0

Hello! First of all, thank you for the great work on maintaining fs-extra 🙇

With Node.js 10.1.0 recently released, we started to see the following warning in our test suite:

(node:7885) ExperimentalWarning: The fs.promises API is experimental

It turns out the fs module provides a new property promises which triggers the warning on the first access.

You can try it out yourself:

$ node -v
v10.1.0
$ node -e "console.log(typeof fs.promises)"
object
(node:8277) ExperimentalWarning: The fs.promises API is experimental

On Node.js version 10.0.0:

$ node -e "console.log(typeof fs.promises)"
undefined

Can we fix lib/fs/index.js to not emit ExperimentalWarning until the experimental API is actually accessed?

[bajtos]

Proposed fix: #578

[jdalton]

Related Node PR: nodejs/node#20504.