ts-jest warns about babel-jest not installed when used in yarn 2 workspace

[brandonchinn178]

🐛 Bug Report

Yarn 2 has workspaces, where you have a top-level package.json, with subdirectories having their own package.json. If a workspace has ts-jest and babel-jest installed, with babelConfig set, ts-jest will warn

ts-jest[versions] (WARN) Module babel-jest is not installed. If you're experiencing issues, consider installing a supported version (>=27.0.0 <28.0.0-0).

even though it actually finds babel-jest correctly (ts-jest.log shows "loaded module babel-jest" log).

Doing some debugging, I printed out the error in get-package-version.ts and saw that it shows the usual Yarn 2 Pnp error:

Error: ts-jest tried to access babel-jest, but it isn't declared in its dependencies; this makes the require call ambiguous and unsound.

Required package: babel-jest (via "babel-jest")
Required by: ts-jest@virtual:cdc2a663889160479555b82f11958bfd85b7d15b045b5582042820fdf488eff146d80f22499fcddb05d9aac4969ca161c3fb96119d941ba1ca3ee741a319bc59#npm:27.0.3 (via .../.yarn/$$virtual/ts-jest-virtual-48f1fd0a1a/0/cache/ts-jest-npm-27.0.3-10e7dc0605-a63f3a8620.zip/node_modules/ts-jest/dist/utils/)

Looks like ts-jest just needs to add babel-jest to its peerDependencies list (docs).

To Reproduce

Steps to reproduce the behavior:

1. mkdir repro && cd repro
2. yarn set version berry
3. yarn init
4. mkdir foo && touch foo/package.json
5. Edit package.json to add "private": true and "workspaces": ["./foo"]
6. yarn workspace foo add jest ts-jest typescript babel-jest @babel/core @types/jest
7. Edit jest.config.js to enable ts-jest and turn on babelConfig: true
8. See warning appear

Expected behavior

Warning should not appear.

Link to repo (highly encouraged)

Debug log:

# content of ts-jest.log :

envinfo

System:
    OS:
    Node version:

Npm packages:
    jest:
    ts-jest:
    typescript:
    babel(optional):

[brandonchinn178]

Workaround: add the following to .yarnrc.yml:

packageExtensions:
  'ts-jest@*':
    peerDependencies:
      'babel-jest': '*'

and rerun yarn install

[ahnpnl]

If adding Babel-jest to peer deps, it will make users who don’t use Babel-jest get the warning too. I think it’s just yarn 2 problem itself because yarn 1 doesn’t have this problem.

[brandonchinn178]

It's not a yarn 2 problem (in it being a regression from yarn 1). PnP forces package.json files to be explicit about all of its dependencies. In this case, this is a correct error (that yarn 1 didn't check) that ts-jest is trying to require a dependency it doesn't explicitly mention in its package.json

peerDependenciesMeta exists for the purpose of marking a peer dependency as optional

"peerDependenciesMeta": {
    "babel-jest": {
        "optional": true
    }
}

[ahnpnl]

ah ha i never use that optional before. PR is welcome :)