Yarn Resolutions to Fix Build Error With Multiple Versions of NPM Package

29 January 2020

So, I upgraded Cypress from 3.7.0 to 3.8.2 and ran everything locally - no problems.

But the build failed both in GitHub Actions and Netlify with the following messages:

7:07:06 PM: [3/4] Linking dependencies...
7:07:12 PM: [4/4] Building fresh packages...
7:07:16 PM: error /opt/build/repo/node_modules/@types/testing-library__cypress/node_modules/cypress: Command failed.
7:07:16 PM: Exit code: 1
7:07:16 PM: Command: node index.js --exec install
7:07:16 PM: Arguments:
7:07:16 PM: Directory: /opt/build/repo/node_modules/@types/testing-library__cypress/node_modules/cypress
7:07:16 PM: Output:
7:07:16 PM: Installing Cypress (version: 3.7.0)
7:07:16 PM: [18:07:13]  Downloading Cypress     [started]
7:07:16 PM: [18:07:13]  Downloading Cypress      0% 0s [title changed]
7:07:16 PM: failed during stage 'building site': Build script returned non-zero exit code: 1

Two things stuck out here:

It’s types for testing-library__cypress that fails
Cypress 3.7.0 is being downloaded for installation, even though I just upgraded to 3.8.2.

So, the types for Cypress Testing Library has a dependency to version 3.7.0 of Cypress, but of course I only want one version of it. When using Yarn, this can be solved with Selective dependency resolutions, by adding the following to package.json:

"resolutions": {
    "cypress": "3.8.2"
}

🎉 Success!

I also learned that Yarn has a why command that one can use to find out why a package is installed. yarn why cypress tells me this:

=> Found "cypress@3.8.2"
info Has been hoisted to "cypress"
info Reasons this module exists
   - Specified in "devDependencies"
   - Hoisted from "@testing-library#cypress#@types#testing-library__cypress#cypress"