userHome can get overridden even if process UID is not root

[mattlqx]

Do you want to request a feature or report a bug?
Bug under a certain use-case.

What is the current behavior?
When running Yarn from another process like Chef that can specify UID and doesn't spawn under a new shell, userHome gets overridden even though the effective UID of Yarn is not root. This can lead to Yarn trying to create directories in /usr/local/share even though it may not have permissions to do so.

Result of #1344

This is pretty easy to workaround by simply specifying a USER environment variable (instead of letting it be root, which Chef runs as) in the execute statement, but I think the conditional to override userHome could be improved.

If the current behavior is a bug, please provide the steps to reproduce.

1. Run yarn in a Chef execute statement with a non-root user attribute.

This will fail because the non-root user likely won't have permissions to write to /usr/local/share.

What is the expected behavior?
Run normally and with the user home dir specified by the HOME variable.

Please mention your node.js, yarn and operating system version.
6.9.1, 0.17.0, Ubuntu 16.04

[sebmck]

We don't do this detection ourselves, we use the user-home package. Source is here. I'd recommend opening an issue over there.

[mattlqx]

It actually is overridden somewhat by Yarn here:

yarn/src/constants.js

Lines 4 to 6 in 91267dc

	if (process.platform === 'linux' && process.env.USER === 'root') {
	userHome = path.resolve('/usr/local/share');
	}

That's where the issue stems from.