nix-shell --sandbox for debugging derivations

[lf-]

Is your feature request related to a problem? Please describe.

I was debugging a Haskell derivation yesterday and was stymied by /tmp/username/package.conf.d, which is assumed to be non-shared by the builder, but is not actually. It works fine in a sandboxed build.

Describe the solution you'd like

I would like to be able to create a nix-shell in the sandboxed build environment to debug derivations just as they would be built by the normal build flow. It would also be useful if I could write to $out in this environment, which is currently in the nix store and immutable.

Describe alternatives you've considered

Unsure if any exist.

Additional context

[bjornfor]

Related: https://nixos.org/manual/nixpkgs/stable/#breakpointhook. (Have you seen it?)

[lf-]

Nope, have not seen that but it certainly looks very interesting. I don't think it's the right solution for every case though because it requires the build to be broken to be used.

[18fadly-anthony]

This seems similar to my issue, isolate home folder in nix-shell