Problem: Reference to /tmp/nix-build-* in derivations

[clacke]

$ nix-build -E 'with import ./. {}; (buildRacket { package = "typed-racket-lib"; }).env' | xargs rg /tmp
/nix/store/vzx6jg056bn6s5m7ncxs71ikqkr75050-typed-racket-lib-env/share/racket/pkgs/pkgs.rktd
1:#hash(("typed-racket-lib" . #s(pkg-info (dir "/tmp/nix-build-typed-racket-lib.drv-0/typed-racket-lib/") #f #f)))

I don't even know if anything uses pkgs.rktd, but either way this is impure. I thought installing with --copy would make sure something like this didn't happen.