Native optional devDependencies trick with npm workspaces

Start with the root package.json and optionalDevDependencies/package.json examples, then review the described npm install and npm publish behavior if maintainers decide to document the trick. Done would require an explicit documentation or code request; this report currently provides neither.

Since npm install automatically uses your package.json's workspaces: [ ... ] value to install all workspaces at once, you can take advantage of this with a subfolder that has a package.json like:

// optionalDevDependencies/package.json
{
  "optionalDependencies": {
    "my-optional-dev-dependency": "^1.2.3"
  }
}

and then the root package.json like:

{
  "name": "my-awesome-package-with-optional-dev-dependencies",
  "version": "4.5.6",
  "optionalDependencies": {
    "my-optional-production-dependency": "^10.11.12"
  },
  "devDependencies": {
    "my-required-dev-dependency": "^7.8.9"
  }
  "workspaces": ["optionalDevDependencies"]
}

That way when you run npm install it will install the stuff from ./optionalDevDependencies/package.json's optionalDependencies, BUT when you npm publish it the workspace gets completely ignored and the only things left in the manifest are the required devDependencies and the production optionalDependencies.

I think this is a pretty cool trick! I used it to add all the esbuild targets as optional devDependency items for some testing of raw esbuild binary stuff. I needed some optional devDependency items so that npm would choose the right package for the os/cpu combo

// optionalDevDependencies/package.json
{
  "optionalDependencies": {
    "@esbuild/aix-ppc64": "0.19.11",
    "@esbuild/android-arm": "0.19.11",
    "@esbuild/android-arm64": "0.19.11",
    "@esbuild/android-x64": "0.19.11",
    "@esbuild/darwin-arm64": "0.19.11",
    "@esbuild/darwin-x64": "0.19.11",
    "@esbuild/freebsd-arm64": "0.19.11",
    "@esbuild/freebsd-x64": "0.19.11",
    "@esbuild/linux-arm": "0.19.11",
    "@esbuild/linux-arm64": "0.19.11",
    "@esbuild/linux-ia32": "0.19.11",
    "@esbuild/linux-loong64": "0.19.11",
    "@esbuild/linux-mips64el": "0.19.11",
    "@esbuild/linux-ppc64": "0.19.11",
    "@esbuild/linux-riscv64": "0.19.11",
    "@esbuild/linux-s390x": "0.19.11",
    "@esbuild/linux-x64": "0.19.11",
    "@esbuild/netbsd-x64": "0.19.11",
    "@esbuild/openbsd-x64": "0.19.11",
    "@esbuild/sunos-x64": "0.19.11",
    "@esbuild/win32-arm64": "0.19.11",
    "@esbuild/win32-ia32": "0.19.11",
    "@esbuild/win32-x64": "0.19.11"
  }
}

This isn't really an issue. This is me trying to share this trick that I found that I thought was cool with anyone else who comes across the https://www.npmjs.com/package/optional-dev-dependency package (which is deprecated) or this github repository looking for a way to do optional dev dependencies. 😊
Feel free to close this if this is the wrong place for such stuff. ❤️