Support Yarn PnP module resolution

The Files.resolve function exported by vscode-languageserver fails to resolve node modules in a Yarn PnP environment. This causes for example vscode-eslint to stop working when using PnP (see microsoft/vscode-eslint#601).

In order to support Yarn PnP, the project’s local .pnp.js file needs to be required.

Quick pseudocode for how this should work:

if (is yarn pnp) {
  require(cwd + '/.pnp.js')
}

// ...rest

I think this has to be done at some point during the app script in Files#resolve:

https://github.com/microsoft/vscode-languageserver-node/blob/4d256255c2f2e00a2f6214c581e32ade7c8acc1e/server/src/files.ts#L52-L68

Edit: Or better yet, add --require /path/to/.pnp.js to the node CLI arguments here:

https://github.com/microsoft/vscode-languageserver-node/blob/4d256255c2f2e00a2f6214c581e32ade7c8acc1e/server/src/files.ts#L87-L90

That would be the recommended approach by the Yarn docs.

[dbaeumer]

Discussing this in the ESLint repository is the best location. It was a mistake to add the resolve feature to the server in the first place and I actually will not improve this further. Loading stuff from the workspace folder should be best done by the extension that wants to load these files.

So I close the issue in favour of the having a solution in ESLint.

[teoxoy]

I am using yarn v2 (berry) for a monorepo, taking advantage of pnp and workspaces but vscode-eslint doesn’t work because of this issue.

The problem that I see is that on the consuming side how would a server know that something got installed using yarn --pnp. We would need another setting for this.

pnp comes by default with yarn v2 (berry). Regarding v1, I’m not sure how to check if pnp is enabled or not…

I would like to start a PR myself but there are some unknowns:

• should only yarn v2 be supported?
• how can this feature be tested?