Fix: ensure --stdin flag works when stdin is piped asynchronously

[not-an-aardvark]

What is the purpose of this pull request? (put an "X" next to item)

[x] Bug fix

Tell us about your environment

• ESLint Version: master
• Node Version: 8.11.1
• npm Version: 5.6.0

What parser (default, Babel-ESLint, etc.) are you using?

N/A

Please show your full configuration:

N/A

What did you do? Please include the actual source code causing the issue.

This issue is simplest to reproduce with bash:

$ (echo 'a' && sleep 1 && echo 'b') | eslint --stdin --no-eslintrc

(I originally encountered this issue when using curl to fetch a JS file and pipe it to eslint --stdin.)

What did you expect to happen?

I expected ESLint to read stdin until the end (resulting in two lines of input), and then lint those two lines.

What actually happened? Please include the actual, raw output from ESLint.

An error was thrown:

EAGAIN: resource temporarily unavailable, read
Error: EAGAIN: resource temporarily unavailable, read
    at Object.fs.readSync (fs.js:675:18)
    at tryReadSync (fs.js:540:20)
    at Object.fs.readFileSync (fs.js:583:19)
    at Object.<anonymous> (/path/to/eslint/bin/eslint.js:59:53)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Function.Module.runMain (module.js:693:10)

Based on nodejs/node#7439, this probably only occurs on macOS.

What changes did you make? (Give an overview)

This updates bin/eslint.js to avoid accessing the process.stdin getter, which seems to change the state of file descriptor 0.

Is there anything you'd like reviewers to focus on?

Should this be filed as a Node bug instead? Based on nodejs/node#7439, it seems to at least partially be working as intended, but the behavior is somewhat surprising.

[platinumazure]

LGTM, thanks!

I think we should probably fix here, if the fd property is really undocumented as noted in the issue. I agree that the behavior is surprising, though.

[kaicataldo]

LGTM! Agreed we should fix this here regardless of whether it's an upstream bug in Node itself.