nix why-depends

Show why a package depends on another package. More information: https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-why-depends.html.

• Show why the currently running NixOS system requires a certain store path:

nix why-depends /run/current-system /nix/store/…

• Show why a package from nixpkgs requires another package as a build-time dependency:

nix why-depends --derivation nixpkgs#dependent nixpkgs#dependency