cache: ignore failures replacing package.json

[orangemocha]

As reported in #9696 , npm install fails frequently on slow Windows machines.

This happens because npm uses write-file-atomic to overwrite package.json in the cache, and it is not possible to write atomically to a file in Windows as it is done in UNIX. To replace a file, it cannot be open at the same time, either for reading or for other calls to write-file-atomic.

Failures writing to package.json are already ignored in another place. Not saving cache information here does not seem to be an issue, but can there be a reason why we might not want to do this? @othiym23

Fixes: #7885
Fixes: #9696

[iarna]

I wonder if, instead of just ignoring this, that write-file-atomic should retry for a little bit if it gets EPERM errors during rename (in the same sort of way that graceful-fs provides for other fs calls). Or maybe we should just add rename to graceful-fs (which write-file-atomic already takes advantage of).

[othiym23]

Alexis, could you rebase this against the latest 2.x head so we can see how it's doing with CI? Thanks! (Also, sorry for letting this languish for a bit. We've been busy!)

[joaocgreis]

@othiym23 last commit on 2.x was on December 11, so this is still up to date.

As suggested by @iarna, submitted a PR to graceful-fs: isaacs/node-graceful-fs#55 . That should solve #9696 , but not when multiple npm instances run simultaneously as in #7885 . So this should still land (unless saving the cache here is essential for some reason).

[othiym23]

Hmm... I guess the changes @zkat has made to get the tests passing for 2.x haven't been merged to the branch yet; I'd like to wait for a passing build before we merge this, as this is a significant change. That should happen as part of next week's release, so we'll circle back to this after that's gone out.

[iarna]

This was merged to 3.6.0 & 2.14.16! =)

[orangemocha]

Awesome, thank you!