'corepack prepare' does not read "packageManager" in package.json

[brandon-leapyear]

The docs and comments indicate that corepack prepare should look at the package manager configured in package.json and download it, but it currently doesn't.

Repro

1. docker run --rm -it --entrypoint sh node:16.11.1-alpine3.14
2. echo '{"packageManager": "yarn@3.0.2"}' > package.json
3. ls ~/.node doesn't exist (expected)
4. corepack prepare
5. ls ~/.node doesn't exist (unexpected)
6. corepack yarn --version (shows 3.0.2)
7. ls ~/.node does exist (expected)

[kylemh]

Hey @arcanis

I think fixing this introduced an issue that's worth resolving. If have the packageManager set, but then run a prepare command with a specific version listed, the value is silently ignored and the packageManager value is adhered to. I think it'd be better for the command to fail with a helpful error or at least provide a logging statement to be less silent about the mistake.

[kherock]

@kylemh I don't think this fix has been released yet, unless you have a configuration where you're running corepack from source. Keep in mind that, when defined, packageManager is always adhered to when using corepack yarn, corepack pnpm, etc. To change the package manager version that a project uses, I think you're expected to edit package.json and commit the update.

[kherock]

The docs for corepack <binary name>[@<version>] [... args] kind of dances around this fact:

Note that those commands still check whether the local project is configured for the given package manager (ie you won't be able to run corepack yarn install on a project where the packageManager field references pnpm).

[kylemh]

I am installing in CI and using it from source because I'm on Node 14.

What you're saying is totally fair, and I gathered as much... but only after a lot of investigation. There's nothing wrong with the logic, but the CLI logging offers no notice. I guess I'm suggesting that the config "winner" gets an announced in the output of a ran command.

This isn't a question about docs either. I didn't go to corepack docs because I had no CLI errors or logging which indicated implicit behavior was intercepting my explicit command.