[Bug?]: cannot import xo from a module using PNP

[flying-sheep]

Self-service

• I'd be willing to implement a fix

Describe the bug

I’m trying to create a SDK package for VS Code’s xo linter https://github.com/xojs/vscode-linter-xo

But PnP doesn’t seem to work with import(). Am I doing something wrong?

[Error - 20:01:44] Cannot find package 'xo' imported from ~/dev/<myproject>/.yarn/sdks/xo/index.js

I did specify pnpEnableEsmLoader: true in my yarnrc.yml.

To reproduce

Create the SDK and try to import it

mkdir -p .yarn/sdks/xo
echo '{"type": "module"}' >.yarn/sdks/xo/package.json
cat >.yarn/sdks/xo/index.js <<EOF

import {existsSync} from 'fs'

const relPnpApiPath = '../../../.pnp.cjs'

const { pathname: absPnpApiPath } = new URL(relPnpApiPath, import.meta.url)

if (existsSync(absPnpApiPath)) {
	if (!process.versions.pnp) {
		// Setup the environment to be able to import xo
		const { default: pnp } = await import(absPnpApiPath)
		pnp.setup()
	}
}

// Defer to the real xo your application uses
const { getErrorResults, getFormatter, outputFixes, lintText, lintFiles } = await import('xo')
export { getErrorResults, getFormatter, outputFixes, lintText, lintFiles }

EOF

Environment

System:
    OS: Linux 5.14 Arch Linux
    CPU: (16) x64 AMD Ryzen 7 3700X 8-Core Processor
  Binaries:
    Node: 16.11.1 - /tmp/xfs-4e63bbf9/node
    Yarn: 3.1.0 - /tmp/xfs-4e63bbf9/yarn
    npm: 8.1.3 - /usr/bin/npm

Additional context

No response

[flying-sheep]

Any help with this? I can’t seem to figure out if import('xo') is supposed to call into your monkeypatched system or if what I’m trying can’t work.

[merceyz]

Using the experimental ESM support requires starting Node with the --experimental-loader flag https://nodejs.org/docs/latest-v16.x/api/esm.html#loaders

[flying-sheep]

I see. With that, I get the server to listen, but it still doesn’t seemt to work 🤔

https://github.com/flying-sheep/react-color-scheme-switch/pull/3/files

[Info  - 16:29:21] XO Server Starting in Node v16.11.1

But “Language Client is not ready yet” if I want to trigger a code action.

[flying-sheep]

C’mon, I thought someone had finally time to check this out, instead I get a bot …

No idea how I can reproduce this in sherlock.

[merceyz]

I looked into it and It looks like you're running into nodejs/node#39140

[flying-sheep]

Thank you so much for helping! xo is an ESM-only package, so I think I have to write the SDK as ESM. I wonder where the bug is. I don’t assume it’s in vscode-linter-xo, as it seems to properly await promises everywhere. https://github.com/xojs/vscode-linter-xo/blob/ddc03f4cbcf47a1e5332dc15bc7daa70c838aeda/server/server.js#L487-L493

I think VS Code handles the actual subprocess spawning and message passing, so maybe this is a race condition in VS Code, that PNP is slow enough to trigger?

[merceyz]

that PNP is slow enough to trigger?

It's not PnP, it's because of ESM (see the issue I linked)

[flying-sheep]

I see! It could still be a race condition (if xo-without-pnp loads fast enough, it won’t trigger the bug), but I should probably just wait for nodejs/node#41134 to be fixed for this, as there’s only 2 reliable fixes:

1. that one
2. make VS code do the handshake that was mentioned in your linked issue.

Thank you! I’ll close this, and if it turns out there’s another issue that looks to be on yarn’s side, I’ll reopen it.

[flying-sheep]

With node 17.4 we can make progress! See #4045