Cannot delete path ... since it is still alive. To find out why, use: nix-store --query --roots, but nix-store --query --roots shows nothing

[ghost]

Describe the bug

Recently, I needed to forcibly rebuild a derivation output. I attempted to delete the old output:

$ nix-store --delete /nix/store/i9qmw2r3d78lma985g7qzipdmqv8jd5d-stdenv-bootstrap-tools-mips64el-linux-gnuabi64
finding garbage collector roots...
0 store paths deleted, 0.00 MiB freed
error: Cannot delete path '/nix/store/i9qmw2r3d78lma985g7qzipdmqv8jd5d-stdenv-bootstrap-tools-mips64el-linux-gnuabi64' since it is still alive. To find out why, use: nix-store --query --roots

After following nix-store's advice, I got:

$ nix-store --query --roots /nix/store/i9qmw2r3d78lma985g7qzipdmqv8jd5d-stdenv-bootstrap-tools-mips64el-linux-gnuabi64
$

Steps To Reproduce

Steps to reproduce the behavior:

This has happened to me a couple of times, but I don't know how to reproduce it, short of shipping you a complete tarball of my /nix/store (and possibly other parts of my system as well).

Expected behavior

A clear and concise description of what you expected to happen.

Either /nix/store/i9qmw2r3d78lma985g7qzipdmqv8jd5d-stdenv-bootstrap-tools-mips64el-linux-gnuabi64 gets deleted, or nix-store --query --roots shows me something that references it, or else the tools print additional instructions for the user.

Screenshots

See above.

Additional context

I do feel like I might be abusing the issue tracker here to get technical support. If so, I will make amends by submitting a PR to improve the documentation and/or error messages printed by nix-store.

Notify maintainers

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

 - system: `"x86_64-linux"`
 - host os: `Linux 5.10.10+, Debian GNU/Linux, 10 (buster)`
 - multi-user?: `no`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.5.0pre20211206_d1aaa7e`
 - nixpkgs: `/nix/nixpkgs`

[Artturin]

NixOS/nix#6141

[ghost]

Ok! At least I'm in good company :)