Added option to disable yarn on initial build to fix jest failure

[thtliife]

When creating an app using yarn / yarnpkg, some binaries do not get properly linked, causing the Jest test scripts to fail.
If yarn is used after using npm for the initial build, everything seems to work fine.
The issue to track regarding yarn binaries should be yarnpkg/yarn#648

This PR adds a --disable-yarn option, which will force the initial build to use npm.

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[thtliife]

Closing and reopening to trigger travisci rebuild

[gaearon]

Can you provide a detailed way to reproduce?

I don’t think we’ll be adding flags specifically for this since people who need them the most won’t know they exist anyway. If you use Yarn, you implicitly agree to be “on the edge” since it’s still new and experimental.

A detailed way to reproduce will help get it fixed sooner.

[thtliife]

@gaearon:

Can you provide a detailed way to reproduce?

I don’t think we’ll be adding flags specifically for this since people who need them the most won’t know they exist anyway. If you use Yarn, you implicitly agree to be “on the edge” since it’s still new and experimental.

A detailed way to reproduce will help get it fixed sooner.

Can you reproduce the problem with latest npm?

No, works fine with npm@4.0.5
Issue occurs if yarn is installed (Currently using yarn@0.18.1)

Description

Jest testing crashes if yarn is used to create the app using create-react-app

Steps to reproduce

Create a new app with yarn as the package manager:

• create-react-app test-app
• cd test-app

Run the default tests with either yarn or npm.

• yarn run test
• npm run test

Expected behaviour

The tests should run, and presumably pass, as no changes have yet been made, with output like:

 PASS  src/App.test.js
  ✓ renders without crashing (24ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.171s
Ran all test suites.

Watch Usage
 › Press p to filter by a filename regex pattern.
 › Press q to quit watch mode.
 › Press Enter to trigger a test run.

Actual behaviour

The test crashes, producing the following output:

Determining test suites to run...2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
2017-01-12 09:18 node[3259] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-22)
events.js:160
      throw er; // Unhandled 'error' event
      ^

Error: Error watching file for changes: EMFILE
    at exports._errnoException (util.js:1022:11)
    at FSEvent.FSWatcher._handle.onchange (fs.js:1283:11)
error Command failed with exit code 1.

Environment

$ npm ls react-scripts
test-app@0.1.0 /Users/username/projects/test-app
└── react-scripts@0.8.5 

$ node --version
v7.4.0

$ npm --version
4.0.5

$ yarn --version
0.18.1

$ uname -v
Darwin Kernel Version 16.3.0: Thu Nov 17 20:23:58 PST 2016; root:xnu-3789.31.2~1/RELEASE_X86_64

$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.12.2
BuildVersion:	16C67

[mattmarcello]

I am experiencing this issue.

[thtliife]

Soo... since upgrading yarn to v0.20.0 (RC) the issue with linking of binaries appears fixed, and new apps created with cra no longer have any problems running tests...
Closing this pr, as it looks like it will not be merged anyway, and it is no longer really required.
Oh and @mattmarcello, try upgrading yarn to the 0.20.0 version, and you should see better results.

[gaearon]

Thanks for the update!