Add System.username

[will]

In discussion of #12604 we determined that a useful shortcut would be to grab the current username directly, which avoids allocating several strings out of the lib passwd struct and the System::User class if the only thing one cares about is the current user name.

Reference #7738

[HertzDevil]

The Windows equivalent is GetUserNameExW but note that a few different formats are available. (IIRC only two or three work on a Windows Home installation) Also it is worth considering whether $USER or %USERNAME% could override this return value.

You might notice that Path.home does a very similar thing, it's up to you whether you want to factor out the code for getpwuid_r.

Personally I prefer it being a class method of just System, rather than System::User.

[will]

Also it is worth considering whether $USER or %USERNAME% could override this return value.

For this part, my thinking was to have the stdlib do the harder thing of making system calls, and leave the choice of checking env vars up to user code, if the situation should or shouldn't respect env vars being different than the result of getuid or GetUserNameExW.

[will]

Personally I prefer it being a class method of just System, rather than System::User.

I pushed two fixup commits to do this, one to just do it, and another to refactor out the duplicate code.

I left the windows part out for myself, since I don't have a way to test that at the moment, and while I could make a VM or something, it'll realistically be several weeks before I could find time to get that all working, so maybe someone else could pick that part up?

[straight-shoota]

I'd suggest to call this method System.username. It's more concise and follows the same scheme as System.hostname.

[asterite]

I'd suggest to call this method System.username. It's more concise and follows the same scheme as System.hostname.

Can you have multiple hostnames configured in a system, and a current one being used? Can you have multiple usernames in a system and a current one being used?

[HertzDevil]

On POSIX there are the differences between the real user, the effective user, and the login user ($LOGNAME). Windows probably has similar differences.

[will]

I'd suggest to call this method System.username.

I made this change in the last fixup

edit: made a mistake with git, one second fixed

[Sija]

I'd suggest using an early-return.

Suggested change

	String.new(pwd.pw_name)
	else
	raise RuntimeError.from_errno("Could not get current user name")
	end
	return String.new(pwd.pw_name)
	end
	raise RuntimeError.from_errno("Could not get current user name")