Add support for new yarn workspaces config format

[detrohutt]

With the addition of the nohoist feature, yarn has enabled a new optional format for the workspaces key in package.json:

"workspaces": {
   "packages": ["packages/*"],
    "nohoist": ["**"]
}

This feature is already available in the current yarn nightly build and I'm successfully using it with the following setup:

[email protected] (nightly)
[email protected] (with my patch)
[email protected] (with a similar patch)

With these patches applied, everything worked out-of-the-box*, aside from needing to make use of the nohoist option.
*(obviously, I also needed to configure lerna to use yarn and workspaces)

With the nightly build of yarn installed all enabling nohoist required was:

1. Adding the settings shown above to my package.json
2. Adding the following to my .yarnrc:

--workspaces-experimental true
--workspaces-nohoist-experimental true

I could put together a demo lerna repo with my patches applied if needed, but I'm pretty busy with my current project, so if it's not necessary I won't bother.

Similarly, I'd be willing to add a new test to prove it gets the values from workspaces.packages when present. But I'm wondering if that's overkill for such a simple change.

Let me know if you have any questions or concerns! :)

[detrohutt]

The build error I'm seeing:

TypeError: Cannot read property 'loose' of undefined (While processing preset: "/tmp/tmp.uBrV9CToKQ/yarn-ws/node_modules/babel-preset-react-app/index.js")

This doesn't seem related to my change..

[iansu]

@bradfordlemley how does this fit with the monorepo work you're doing?

[bradfordlemley]

Cool!
It's not necessary to use nohoist for any CRA-related stuff, but definitely want to support this workspace definition format.

Note: #3997 fixes the "'loose' of undefined" error and also moves the code that this PR is modifying.

[detrohutt]

Thanks for the heads up! I'll be glad to update my PR as soon as #3997 is merged.

[detrohutt]

@bradfordlemley I see the PR was merged. I'm updating mine now. It's still going to be a one-liner. Should I add a test? If so, is there a similar test I could base it off of? I'm not at all familiar with CRA's test suites since this is my first code commit.

[bradfordlemley]

Tests are in e2e-monorepos.sh. In my opinion, an additional test isn't necessary.

[detrohutt]

Alright, I've updated it. I manually tested by doing this:

• ran yarn create-react-app test-app
• copied test-app into the /packages/test-app of a lerna repo of mine with nohoist enabled
• copied test-app to ~/git/test-app (not a monorepo)
• ran yarn start from within each of the 3 copies:
  • monorepo without nohoist
  • monorepo with nohoist
  • standard repo

All worked fine. Let me know if I need to do anything else!

[bradfordlemley]

Looks good to me!