Support absolute paths with packages/ folder

Created by: gaearon

We’ve been using Lerna in Create React App, and I really like its approach. I think we should support a similar workflow (even without Lerna itself) for the “absolute paths” feature.

I imagine it working like this:

• In addition to src, you can create a special top-level folder called packages.
• Inside packages, you can create folders like app, stuff, lol, and they all “see” each other so you can import things from app/whatever.js or lol/wow.js. You can also import any packages from src (but not vice versa). The entry point is still src/index.js.
• We won’t add any magic handling that breaks Node resolution mechanism. Instead, whenever you npm start, npm test, or npm run build, we will run a utility that creates symlinks from node_modules of the root project to every folder in packages. It reports a hard error if there is a conflict. This means the authors can add server rendering after ejecting without scratching their heads, and that all the tooling assuming Node resolution mechanism keeps working.

package.json
public/
src/
  index.js # can import app/banana.js or harry-potter/wand.js
packages/
  app/
    banana.js # can import harry-potter/wand.js
  harry-potter/
    wand.js # can import app/banana.js
node_modules/
  app -> packages/app
  harry-potter -> packages/harry-potter
  other-deps

Am I missing why this would be a bad idea?