ExperimentalWarning: The fs.promises API is experimental

[ofrobots]

From @kriskate on June 25, 2018 21:56

Environment details

• OS: macOS High Sierra
• Node.js version: 10.1.0
• npm version: 5.6.0
• @google-cloud/logging-winston version: 0.9.0

Steps to reproduce

import { LoggingWinston } from'@google-cloud/logging-winston'

I receive the console error
(node:27103) ExperimentalWarning: The fs.promises API is experimental
which is unfortunate because I'm redirecting the console to the logger and always get this error in Stackdriver as well

Copied from original issue: googleapis/nodejs-logging-winston#105

[ofrobots]

Hi @kriskate! Thanks for the bug report. Given that you're using ES6 modules can you also provide details on how you are using them? E.g. are you using babel or TypeScript, and if so, what versions.

Secondly can you run with the Node.js --trace-warnings flag so that we can see the stack trace leading to the warning? node --trace-warnings index.js.

[ofrobots]

From @kriskate on June 25, 2018 23:39

Hey, thanks for the prompt response.
requiring the modules has the same result
let LoggingWinston = require('@google-cloud/logging-winston')

(node:33405) ExperimentalWarning: The fs.promises API is experimental
    at Object.get [as promises] (fs.js:84:15)
    at __importStar (~/node_modules/google-auth-library/build/src/auth/googleauth.js:58:96)
    at Object.<anonymous> (~/node_modules/google-auth-library/build/src/auth/googleauth.js:65:10)
    at Module._compile (internal/modules/cjs/loader.js:678:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:689:10)
    at Module.load (internal/modules/cjs/loader.js:589:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:528:12)
    at Function.Module._load (internal/modules/cjs/loader.js:520:3)
    at Module.require (internal/modules/cjs/loader.js:626:17)
    at require (internal/modules/cjs/helpers.js:20:18)

[ofrobots]

Thanks! I believe this is an issue in the google-auth-library module so I am going to move the issue there.

[ofrobots]

This is due to use of import * from 'fs' here: https://github.com/google/google-auth-library-nodejs/blob/b82d2c401089390813ee9edcda634ec14853e36e/src/auth/googleauth.ts#L20-L26

We should avoid using import * for Node built-in module now that we are using TS synthetic imports.

[ofrobots]

We should also look into a lint rule to prevent this from happening elsewhere.

[JustinBeckwith]

I actually changed this back to a * import in #382 🤣

Synthetic imports on node core libraries only seem to work if downstream TypeScript users also have enabled synthetic imports.

The warning is harmless FWIW.

[ofrobots]

The warning is disconcerting for users.

I see #382. We should drop esModuleInterop from our TS config. WDYT?

[kriskate]

Wouldn't importing from fs/promises solve the issue?

Alternatively, maybe using esmodules for when compiling with tsc might help, according to microsoft/TypeScript#22851. The thread also says something about __importStar, which is used to load the credentials I'm passing through keyFilename. Please have a look.

[ofrobots]

@kriskate we actually do not use fs.promises at all. The warning is being generated due to the implementations details of how TypeScript generates code for import *. It iterates all properties of the fs module object and in doing so it accesses fs.promises even though we don't need to use it.

Similarly, we cannot use esmodules in the target setting because we support users running with Node 6.

[ofrobots]

The experimentalWarning seems to be fixed with Node 10.2.0+ due to nodejs/node#20403.