error: undefined variable ‘placeholder’ at colord/default.nix:32:48

[davidak]

Issue description

imac:~ davidak$ nix-env -i wkhtmltopdf
error: undefined variable ‘placeholder’ at /nix/store/gzi9hjqk7lbal4dw0q5k2pjml3pbjkfj-nixpkgs-18.09pre133642.5adec8d6c18/nixpkgs/pkgs/tools/misc/colord/default.nix:32:48

cc @jtojnar

Steps to reproduce

imac:~ davidak$ nix-channel --list
nixpkgs https://nixos.org/channels/nixpkgs-unstable

imac:~ davidak$ nix-channel --update
downloading Nix expressions from ‘https://d3g5gsiof5omrk.cloudfront.net/nixpkgs/nixpkgs-18.09pre133642.5adec8d6c18/nixexprs.tar.xz’...
downloading ‘https://d3g5gsiof5omrk.cloudfront.net/nixpkgs/nixpkgs-18.09pre133642.5adec8d6c18/nixexprs.tar.xz’... [1167/10066 KiB, 1164.5 KiB/s]
unpacking channels...
created 2 symlinks in user environment

Technical details

darwin
nixpkgs-unstable channel

[bjornfor]

Ref. #37693

[davidak]

Problem due to old Nix version. master needs 2.0 (see Ref.)