Replace Yarn v1 (Classic) as package manager

[MikeMcC399]

What would you like?

Replace Yarn Classic v1 as package manager for building Cypress from source. The documentation CONTRIBUTING > Getting Started describes how Yarn is used with Cypress.

Why is this needed?

Yarn Classic v1 used by Cypress is unsupported since January 2020.

Although the npm module Yarn is still showing 6 Million downloads a week (see also trends), the Yarn 1 GitHub repo contains the "About" text:

The 1.x line is frozen - features and bugfixes now happen on https://github.com/yarnpkg/berry"

The Yarn Classic v1 documentation says:

These instructions only cover Yarn versions prior to 2.0. Those versions entered maintenance mode in January 2020 and will eventually reach their end-of-life in terms of support. Please see the main website for the most up-to-date documentation: yarnpkg.com/getting-started/migration.

The Yarn Modern documentation recommends upgrading.

Other

Choice within the Yarn family is unclear:

• The Yarn v1 CI nightly workflow is broken and only tests against end-of-life Node.js versions.
• No end-of-life has been declared for Yarn v1.
• Yarn v1 may be needed to install Yarn Modern if corepack is not used.
• Yarn Modern installation recommends enabling corepack to install Yarn Modern
• corepack, as supplied through Node.js, is marked with Stability 1 Experimental with the remark "Use of the feature is not recommended in production environments."
• Other related players such as Angular are also still using Yarn v1.