Implement `yarn --version` and/or `yarn --help`

[aduh95]

I was trying to build Yarn Switch in a sandboxed environment (Nix in case that matters), and it fails the version check:

$ yarn --version
Error: Missing home folder

› yarn […ARGSN]
$ yarn --help
Error: Missing home folder

› yarn […ARGSN]

IMO it would make sense for yarn --version to give version numbers for both Yarn Switch, and if available the local yarn. Alternatively, there could be some env variable to let the user chose if it wants the Yarn Switch version rather than the Yarn one.

[arcanis]

I believe yarn --version is failing because Yarn Switch attempts to download Yarn into the cache folder to then execute it. You don't have a HOME environment variable to tell Yarn Switch where to put the cache, so it fails and doesn't execute --version at all. The lack of HOME is a little strange; I assume it might be a Nix specificity?

I think running yarn switch --version however should tell you the Yarn Switch version.

[aduh95]

$ yarn switch --version
Error: Missing home folder

› yarn […ARGSN]

The lack of HOME is a little strange; I assume it might be a Nix specificity?

The goal of the sandbox is to maximize build reproducibility, so it filters out env variables and forbid accessing FS access outside the sandbox (and network calls, etc). If the software builds, pass its tests, and can output its version from within the sandbox, you're guaranteed the build is reproducible.

[DimitarNestorov]

If you're going to manage Yarn with Nix you might as well not use "Yarn Switch". Made a derivation here: NixOS/nixpkgs#485402