homeless-shelter writable and causes failure if something writes there

[terlar]

If running nix-portable with sandbox = false and a derivation writes to HOME you will get an error like this:

error: home directory '/homeless-shelter' exists; please remove it to assure purity of builds without sandboxing

I noticed this when trying to build this:
nix-community/NixOS-WSL#481

Perhaps this folder can ensure it is not writable. Or if it is possible to solve in another way.

[SuperSandro2000]

/homeless-shelter should not exist but should be writeable.

Possible solutions:

• remove it after/before each build
• map it to /var/empty (might break other things)
• use bwrap/chroot
• enable the sandbox