Why is automatic chroot store only available on linux and not MacOS?

[arianvp]

Is your feature request related to a problem? Please describe. I'd like to use Nix without /nix on MacOS as it's a major pain to create it.

I saw this recent patch that makes nix use a chroot store automatically if /nix doesn't exist. This sounds like exactly what I want!

https://github.com/NixOS/nix/blob/04e74f7c8bb5589dec578dd049013d3cd2554e65/src/libstore/store-api.cc#L1349-L1373

but it's #if __linux__'d. I was wondering why? as MacOS has chroot() support AFAIk and nix build --store ./my-store seems to work fine on MacOS

Describe the solution you'd like

Remove the #if __linux__.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

Additional context Add any other context or screenshots about the feature request here.

[arianvp]

This condition was added in https://github.com/NixOS/nix/pull/6714/commits/30d4aa5dd651813578b67d70ffbcd0446f6f0fe7 but it doesn't explain why it would only work on linux. In my mind this should work fine on MacOS

[thufschmitt]

as MacOS has chroot() support AFAIk and nix build --store ./my-store seems to work fine on MacOS

I might be mistaken (I don't really know MacOS and I don't have a Mac without Nix to try), but I think this won't work if /nix doesn't exist. AFAIU it's because although chroot exists OSX doesn't have mount namespaces or bind-mounting, so the sandbox is implemented using a totally different mechanism (sandbox-exec) which just allows filtering which paths are visible, but not remap them. Meaning that Nix can't fake a /nix directory like it does on Linux

[abathur]

I'd like to use Nix without /nix on MacOS as it's a major pain to create it.

Not to sidetrack this, but what about creating /nix isn't working? (AFAIK the installer can handle this in most cases; the only asterisk I think I know about is macs that are enrolled in an MDM that uses a policy to keep them from mounting volumes at all?)