Fix symlink resolving for examples in the repo

[Kureev]

Motivation:
Few days ago @gaearon filed an issue that examples in the react-native repo doesn't work after the recent changes in local-cli. This PR fixes reported bug.

Test plan (required)

• No UI changes
• Run UIExplorer from XCode (no package.json in the folder) and check if packager/application runs correctly

cc @davidaurelio @satya164 @grabbou

[Swaagie]

A similar fix, among others, were posted 2 days ago, #12400. Aside from the addtional fixes, I like this cleaner approach to config btw, the hardcoded NODE_MODULES was resolving to a wrong directory when RN itself is symlinked

[Kureev]

Hi @Swaagie! Thanks for your PR, it looks really great. I think we can find a way how we can combine our PRs and ship both. I love the work you did with scoped modules, that's just great! Also, you caught a bug with projectRoots. I think it's a very valuable contribution to the project.

Maybe we can wait someone to review our PRs and find how we can merge them. I think in either case the merge is not going to be that big.

[Swaagie]

Sounds like a plan.

[gaearon]

Thanks for the quick fix!

[Kureev]

Rebased in a hope it'll fix CI builds

[ericvicenti]

I can not repro the issue on master. Do we still need this?

[gaearon]

By can't repro, do you mean it doesn't crawl to folders above, or that you just don't see the same error? My issue description is specific to my computer—if you don't have a broken symlink, you won't see the same error. But the problem is it crawls parent directories in the first place.

[gaearon]

This is the key part of my report:

You won't see the same error if you don't have broken symlinks in a folder above.

[Kureev]

I just double-checked the code in master and it still looks broken. That's how you can reproduce this issue on Mac:

• In the folder where you have react-native repo run:

  $ ln -s foo ./bar
  

  (here I assume that "bar" doesn't exist and symlink is broken)
• Go to react-native/examples/UIExplorer and open UIExplorer.xcodeproj
• Run

You should see something like this:

[Kureev]

I'd also like to explain the reason why this issue occurs: there is the line that defines a path to node_modules as ../../../ (because usually local-cli is located in node_modules/react-native/local-cli which is apparently not the case if you run a project from examples in RN repo: react-native/examples/UIExplorer).

Let me know if you need any additional information to review this PR. Also, feel free to ping me on Slack.

[ericvicenti]

Thanks @Kureev, this is a well documented fix. My apologies for glossing over the important detail. I'll land it now.

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