you did not specify `--add-root'; the result might be removed by the garbage collector /nix/store/ic243k5dw29knvgp60x8nh22kmkbg4dh-hello.drv % nix-instantiate -E ' (import ./ourlib.nix).writeText "hello" "world" ' warning: you did not specify `--add-root'; the result might be removed by the garbage collector /nix/store/ic243k5dw29knvgp60x8nh22kmkbg4dh-hello.drv
/nix/store/ic243k5dw29knvgp60x8nh22kmkbg4dh-hello.drv building path(s) `/nix/store/ p30mrskrnk8y5zvknc7ccppz3m30vkbf-hello' warning: you did not specify `--add-root'; the result might be removed by the garbage collector /nix/store/p30mrskrnk8y5zvknc7ccppz3m30vkbf-hello realising the derivation