plugnplayWindowsSupport warning because of drive letter case mismatch

[codepunkt]

When running yarn --pnp in directory 'D:\projectName', this pops up:

warning Plug'n'Play on Windows doesn't support the cache and project to be kept on separate drives

The cache directory is configured as 'd:\.yarncache', yarn cache dir returns 'd:\.yarncache\v4'.
Afaik, windows drive letters in paths are case insensitive, but the code around line 400 of src/config.js does not account for that and produce a mismatch between cacheRootFolderDrive and lockfileFolderDrive, resulting in the warning shown above.

It would be nice if this could be fixed.

specs: windows 10, yarn 1.13.0, node 10.15.1

[codepunkt]

Even if i do yarn config set cache-dir D:\.yarncache and can read this out well with yarn config get cache-dir, the cache dir drive letter is still lowercase.

see #6447 & #6447 (comment)

/cc @vkrol @jdalton @arcanis

[arcanis]

Makes sense to me. Wanna add the toLowerCase here and add an entry in the changelog? 🙂

[codepunkt]

@arcanis I'm not sure if and how this could be tested. Just adding the toLowerCase twice like i did in my local cli.js sounds doable.

[arcanis]

Yeah, this one will be a pain to test. The best way would be to setup a mock, but that would complexify our whole test infra for a corner case. I'm fine with no tests for this one if Flow passes.