Detect the React and Flow versions relative to the file being linted.

[jcrosetto]

This fixes #2218. This changes version.js to detect the React and Flow versions relative to the file being linted.

[ljharb]

Thanks! Can you perhaps add some tests without altering the existing ones?

[jcrosetto]

You're welcome! I can't wait to get this in. :)

Basically all I did was swap out using process.cwd() with context.getFilename() when determining the version number. The existing tests needed to be updated because they relied on process.cwd() being used. I changed them to work with context.getFilename() instead.

I didn't add any new tests since the changes I made don't really change the expected output. There wasn't anything new or different to test per say. If you can think of something that needs testing I would be happy to add it.

[ljharb]

The issue this fixes is that with nested dirs and deps, the wrong version is detected. To test this, I think we'd need some fixture files that replicate the issue, and verify that the version is detected properly.

[jcrosetto]

That makes sense. I'll put together a test that replicates it.

[jcrosetto]

Added tests that verify versions are correctly detected for both sibling and child projects. @ljharb Let me know if this adequately covers what you were thinking.

[ljharb]

I'm still a bit confused; the existing tests use process.chdir, but presumably your fix would make them work even without that - so why can't the chdir be preserved?

[jcrosetto]

It isn't needed anymore. The purpose of process.chdir was so that process.cwd would pick up the correct directory in version.js. You are correct that leaving it in there wouldn't affect the tests, but I think leaving it in would cause confusion as to what purpose it serves.

[ljharb]

I tweaked the test a bit to use sinon instead of reassignment, otherwise LGTM!