[Nix-dev] CUPS+Gutenprint -- my problem or a bug?

[ab]

As of latest unstable channel at the moment of writing (6221af50), 
CUPS+gutenprint is broken for me in the following ways:

1. Autodetection of a (USB) printer does not work. Nevertheless, CUPS 
usb backend correctly identifies a printer (and gives a URL) when ran 
directly. Access rights for /dev/bus/usb-node seems to be right (664 
root/lp, though with some strange additional ACL granting write to my 
user, too).
2. If I add printer via "lpadmin" using URL generated by a backend, I 
cannot supply a PPD file for it. If I try to give CUPS a PPD file 
generated by "cups-genppd.5.2" (either via web interface or "lpadmin"), 
it fails with "No such file or directory". Of course, the file does 
exist, and when I try to point "lpadmin" to a really non-existent place, 
it fails with a slightly different error (same no-such-file, but with 
path added this time).

I use https://nixos.org/wiki/Printers guide for my setup -- it worked 
nice before the Big Update in the channels (maybe a week ago) which also 
bumped CUPS' version.

I don't have practically any time for researching this (and a lot of 
other things, too -- deadlines!) before the New Year, but after that 
I'll probably dig into it. It would be very nice for someone with a USB 
printer to share his experience -- I don't know if this is a Nixpkgs bug 
or my problem caused by something. If this is really a bug, it probably 
affects 14.12 too, and is a fairly serious thing in my opinion.

-- 
Nikolay.