Resolve symlinks using Node resolution mechanism

Copying my comment from #1107 since that issue is pretty crowded and I want it to be here instead.

---

Having read some discussions in https://github.com/nodejs/node/pull/6537 and https://github.com/isaacs/node6-module-system-change I think we’re actually already being inconsistent in how we handle symlinks.

Let’s forget about the issue about compiling source code for a second. I feel like that can be solved by https://github.com/facebookincubator/create-react-app/issues/1333 and thus is not the most important one here.

The important part here is that the resolution should match Node algorithm so that our webpack setup matches our test setup. I thought that was the case, but I was wrong.

Consider this structure:

my-comp
  index.js // already compiled
  package.json // react is a peer dependency

my-app
  node_modules
    my-comp // symlink to my-comp folder

It turns out that if my-comp doesn’t declare a dependency on react, it can find React in the browser builds but not in tests.

We introduced this regression in https://github.com/facebookincubator/create-react-app/pull/1359.

We probably missed it because if my-comp does explicitly depend on React (e.g. as a devDependency), the test passes (and in the browser we just get two Reacts).

[gaearon]

I think the correct fix would be to:

• Have the webpack build respect Node resolution and fail in this case
• Add an opt-in to Node “preserve symlinks” behavior which seems to be what people using npm link really want

[pietmichal]

Is there a scenario where someone would prefer having dependencies read from linked node_modules instead from CRA-based project’s node_modules? Modifying webpack.config.js to have { resolve: { symlinks: false } } fixes the “two react” problem.

If there is no scenario, then maybe CRA should have the value, from above, hardcoded?