Add --set-home to sudo invocation

[mkenigs]

It is assumed that dirs::home_dir() refers to root's home directory.
This is used, for example, to setup a root profile with nix-env in
SetupDefaultProfile.

dirs::home_dir() is derived from $HOME, but on macOS, by default
sudo does not set $HOME to root's home unless
--set-home is passed.

> sudo bash -c 'echo $HOME'
/Users/matthew
> sudo --set-home bash -c 'echo $HOME'
/var/root

Pass --set-home to the sudo invocation so that $HOME is always
set, regardless of the system's security policy.

[cole-h]

Diff LGTM, just tested and seems to behave fine!

However, I am curious: what's the benefit of doing this? When will having the wrong HOME cause issues? As far as I can tell, the upstream Nix installer also doesn't use --set-home.

[mkenigs]

The issue is that the nix profile will be set up for the current user rather than root.

Upstream explicitly sets HOME="$ROOT_HOME" where ROOT_HOME is set to ~root https://github.com/NixOS/nix/blob/74130fd1f12f7f0e941c5e352fe19811583fe6e3/scripts/install-multi-user.sh#L850

And here there's HOME set to dirs::home_dir()

nix-installer/src/action/base/setup_default_profile.rs

Line 182 in 5ecf3c4

dirs::home_dir()

I'm not quite sure what ~root does, maybe check in /etc/passwd? I guess that would be another approach.

[cole-h]

Gotcha, I missed that -- OK, that makes sense. Thanks, added to the batch in #922.

[mkenigs]

Thanks!