Use Yarn 2

[nicolo-ribaudo]

Q	A
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	👍
License	MIT

Prev: #11142

---

NOTE to whoever rebases this PR

To solve conflicts related to the workspace: protocol in package.jsons, use this script:

const cp = require("child_process");
const fs = require("fs");

cp.execSync("git checkout --ours .");

const allPkgs = ["codemods", "eslint", "packages"].flatMap(
  dir => fs.readdirSync(dir).map(d => `${dir}/${d}/package.json`)
).filter(p => {
  try {
    fs.readFileSync(p);
    return true;
  } catch {
    return false;
  }
});

const allNames = allPkgs.map(p => require(process.cwd() + "/" + p).name);

for (const pkg of allPkgs) {
  const p = JSON.parse(fs.readFileSync(pkg, "utf8"));
  let updated = false;

  for (const d of ["dependencies", "devDependencies"]) {
    if (!p[d]) continue;

    for (const [name, version] of Object.entries(p[d])) {
      if (allNames.includes(name) &&!version.startsWith("workspace:")) {
        p[d][name] = `workspace:${version}`;
        updated = true;
      }
    }
  }

  console.log(pkg, updated);
  if (updated) fs.writeFileSync(pkg, JSON.stringify(p, null, 2) + "\n");
}

[JLHwung]

(😢We are cursed by not using PnP)

[nicolo-ribaudo]

Actually, after yarnpkg/berry#955 we don't need to cache it anymore!

[JLHwung]

That PR is merged, guess we can get rid of the cache?

[nicolo-ribaudo]

Ready!

Thanks @arcanis and @larixer for the help ❤️

[nicolo-ribaudo]

New failure which wasn't there before the rebase 🙃

[arcanis]

Interesting, I tried locally but can't repro it 🤔 Can you try pushing an empty commit to run the test again while preserving the logs for future reference? I wonder if it's consistent. Printing the n_m content might also help shed some light.

[nicolo-ribaudo]

@arcanis The problem was caused by accidentally caching node_modules on Windows. No, it's still not working.

Currently, Travis CI automatically caches it for JavaScript projects: it might be good to reach out to them asking to automatically cache .yarn/cache (and not node_modules) when using Yarn 2.

[larixer]

@nicolo-ribaudo Please note, that I'm sure that node-modules linker in berry's master is broken at the moment (I have missed the results of require and peer dependency guarantees checks on installed packages), but it will be fixed via this PR:
yarnpkg/berry#1015
Also, I think that caching node_modules should work and actually speed up linking. I think both .yarn/cache and node_modules caching should be beneficial in case of n_m linker

[nicolo-ribaudo]

Yeah, I'm using that PR (not master).

[larixer]

@nicolo-ribaudo I'm hesitant about if it is right to reuse the cached node_modules from the broken version of node-modules plugin?

[nicolo-ribaudo]

So far I have disabled node_modules cache so it's not what is causing problems. I will enable it again when CI is green. (Maybe, because the additional cache size might not be worth 5s of saved linking time)

[nicolo-ribaudo]

The windows build is failing because of a permission problem. The node_modules/@babel/helpers symlink created by Yarn in the root of the monorepo throws EPERM when accessed.

Ctrl+F for realpathSync in https://api.travis-ci.com/v3/job/293683500/log.txt

[nicolo-ribaudo]

It works 🎉 🎉 🎉

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/24241/

[arcanis]

Lgtm - for what it's worth, we also use the Babel repo as part of our E2E tests for the n-m linker, so that should help ensure that this setup will always work.

[nicolo-ribaudo]

⚠️ Use "rebase and merge", it will make it easier to fix conflicts

[nicolo-ribaudo]

I'm counting @arcanis's review for our two-:white_check_mark: policy, since as a Yarn maintainer he is one of the most qualified people out there to review this PR!

[kachkaev]

As of now, CONTRIBUTING.md on next-8-dev and next-8-rebased still says:

Yarn: Make sure that Yarn 1 is installed with version >= 1.19.0.

Should the instructions be changed in a follow-up PR? The doc should probably include tips on how to use yarn2 without uninstalling yarn1 because this is what most devs are still using.

[merceyz]

how to use yarn2 without uninstalling yarn1 because this is what most devs are still using.

Yarn will shell out to the local version in the repository so that isn't an issue.

[arcanis]

The documentation is still up to date - as of this PR the Yarn version is stored within the repository, external contributors only need a global Yarn, regardless of its version.