feat: add @yarnpkg/tools package with detectPackageManager function

[paul-soporan]

What's the problem this PR addresses?

There's currently no standardized way for third-party tools to detect which package manager should be used inside the project, which leads to each tool implementing a different set of heuristics that don't handle all of the edge cases.

How did you fix it?

I created a new @yarnpkg/tools package containing a detectPackageManager function to be used by any tools needing to pick a package manager to use either inside a project or when init-ing a new project.

TODO:

• Fallback to corepack elect at the end (Implements "corepack elect" nodejs/corepack#26)
• Show warnings when there are lockfiles in the home folder that could mess up the pm detection
• Tests, many tests
• Replace detectPackageManager from scriptUtils (in @yarnpkg/core) with detectPackageManagerFromProject
• Possibly add an async implementation too

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.

[andreialecu]

Thanks for this. As for more context on why this is going to be super useful, here are two frameworks that try to detect the package manager but don't handle all the edge cases (particularly they can't detect when used inside workspaces):

Angular: https://github.com/angular/angular-cli/blob/c1512e42742c17ace82e783e8e9c919ae925d269/packages/angular/cli/utilities/package-manager.ts#L34-L58
Nest: https://github.com/nestjs/nest-cli/blob/2271c9e0ba6be1c7a202ef1b67d81407a0ac26d5/lib/package-managers/package-manager.factory.ts#L22-L41

---

An opinion on the name @yarnpkg/tools. While it does look cool, I think it implies that it is something internal to @yarnpkg/* instead of being meant for public consumption.

I'm not sure what a good name would be, going to list some random names for possible inspiration:

@yarnpkg/detect-package-manager (might imply it only detects yarn)
@yarnpkg/which-package-manager
@yarnpkg/package-manager-tools

@yarnpkg/whichpm
@yarnpkg/detectpm
@yarnpkg/pmtools

@yarnpkg/package-manager-manager 😆
@yarnpkg/pmm

@yarnpkg/devtools
@yarnpkg/pm-devtools

I think a good name would be self describing, so just by glancing at it inside a package.json you could get an idea about what it's supposed to be for.

[merceyz]

The name really depends on what we want this package to do, @paul-soporan do you have any plans of adding install, add, remove, update functions as well?

To add to the examples @andreialecu provided, cordova could also benefit from this. apache/cordova-cli#292 (comment)

Possibly add an async implementation too

You can use https://github.com/loganfsmyth/gensync to write it once while supporting both sync, async, and callback based functions.
Example here https://github.com/babel/babel/blob/b2d9156cc62d37f4c522c9505a00f50b99a1eb74/packages/babel-core/src/transform-file.ts#L26-L40

[andreialecu]

Also ionic: ionic-team/ionic-cli#4483

Relevant: https://github.com/ionic-team/ionic-cli/blob/868e61d70c54023e39896b677ceac331b0606167/packages/%40ionic/cli/src/lib/utils/npm.ts

[andreialecu]

This will be a problem with Yarn 10 😆