Add --use-yarn flag to create-next-app

[akd-io]

Goals

1. Add --use-yarn flag to create-next-app, similar to --use-npm and --use-pnpm.

Non-Goals

No response

Background

In Create Next Stack, I currently have to fake the npm config user agent in order to force an install with Yarn.

Code in question is here: https://github.com/akd-io/create-next-stack/blob/develop/packages/create-next-stack/src/main/plugins/next.ts#LL84C29-L84C29

The reasoning for requesting support for --use-yarn is well described in the code. I quote:

Below, we temporarily modify the npm_config_user_agent environment variable to make create-next-app use the correct package manager to install dependencies.
This is done because create-next-app doesn't support --use-yarn.
Instead, users of create-next-app are supposed to use yarn create next-app to use create-next-app with Yarn.
This won't work for us though, as Yarn create doesn't support versioned package names, which we need to use to use the correct version of create-next-app.

That is, yarn create next-app isn't as powerful as npx create-next-app, so we need to call it using npx. But create-next-app does not support --use-yarn, so we hack it by calling create-next-app with a fake npm config user agent.

Proposal

Steps:

• Implement --use-yarn flag
• Update docs
• Add tests

I am providing the following PR: #49407

[akd-io]

#49407 was merged

[konradbjk]

Guys it does not work, it does not install yarn properly. I am always getting yarn classic vs yarn berry