Change:
<ins> { config, lib, pkgs, ... }: with lib; let cfg = config.hardware.printers; ppdOptionsString = options: optionalString (options != {}) (concatStringsSep " " (mapAttrsToList (name: value: "-o '${name}'='${value}'") options) ); ensurePrinter = p: '' ${pkgs.cups}/bin/lpadmin -p '${p.name}' -E  ${optionalString (p.location != null) "-L '${p.location}'"}  ${optionalString (p.description != null) "-D '${p.description}'"}  -v '${p.deviceUri}'  -m '${p.model}'  ${ppdOptionsString p.ppdOptions} ''; ensureDefaultPrinter = name: '' ${pkgs.cups}/bin/lpoptions -d '${name}' ''; # "graph but not # or /" can't be implemented as regex alone due to missing lookahead support noInvalidChars = str: all (c: c != "#" && c != "/") (stringToCharacters str); printerName = (types.addCheck (types.strMatching "[[:graph:]]+") noInvalidChars) // { description = "printable string without spaces, # and /"; }; in { options = { hardware.printers = { ensureDefaultPrinter = mkOption { type = types.nullOr printerName; default = null; description = '' Ensures the named printer is the default CUPS printer / printer queue. ''; }; ensurePrinters = mkOption { description = '' Will regularly ensure that the given CUPS printers are configured as declared here. If a printer's options are manually changed afterwards, they will be overwritten eventually. This option will never delete any printer, even if removed from this list. You can check existing printers with <command>lpstat -s</command> and remove printers with <command>lpadmin -x &lt;printer-name&gt;</command>. Printers not listed here can still be manually configured. ''; default = []; type = types.listOf (types.submodule { options = { name = mkOption { type = printerName; example = "BrotherHL_Workroom"; description = '' Name of the printer / printer queue. May contain any printable characters except "/", "#", and space. ''; }; location = mkOption { type = types.nullOr types.str; default = null; example = "Workroom"; description = '' Optional human-readable location. ''; }; description = mkOption { type = types.nullOr types.str; default = null; example = "Brother HL-5140"; description = '' Optional human-readable description. ''; }; deviceUri = mkOption { type = types.str; example = [ "ipp://printserver.local/printers/BrotherHL_Workroom" "usb://HP/DESKJET%20940C?serial=CN16E6C364BH" ]; description = '' How to reach the printer. <command>lpinfo -v</command> shows a list of supported device URIs and schemes. ''; }; model = mkOption { type = types.str; example = literalExample '' gutenprint.''${lib.version.majorMinor (lib.getVersion pkgs.cups)}://brother-hl-5140/expert ''; description = '' Location of the ppd driver file for the printer. <command>lpinfo -m</command> shows a list of supported models. ''; }; ppdOptions = mkOption { type = types.attrsOf types.str; example = { "PageSize" = "A4"; "Duplex" = "DuplexNoTumble"; }; default = {}; description = '' Sets PPD options for the printer. <command>lpoptions [-p printername] -l</command> shows suported PPD options for the given printer. ''; }; }; }); }; }; }; config = mkIf (cfg.ensurePrinters != [] && config.services.printing.enable) { systemd.services."ensure-printers" = let cupsUnit = if config.services.printing.startWhenNeeded then "cups.socket" else "cups.service"; in { description = "Ensure NixOS-configured CUPS printers"; wantedBy = [ "multi-user.target" ]; requires = [ cupsUnit ]; # in contrast to cups.socket, for cups.service, this is actually not enough, # as the cups service reports its activation before clients can actually interact with it. # Because of this, commands like `lpinfo -v` will report a bad file descriptor # due to the missing UNIX socket without sufficient sleep time. after = [ cupsUnit ]; serviceConfig = { Type = "oneshot"; }; # sleep 10 is required to wait until cups.service is actually initialized and has created its UNIX socket file script = (optionalString (!config.services.printing.startWhenNeeded) "sleep 10n") + (concatMapStringsSep "n" ensurePrinter cfg.ensurePrinters) + optionalString (cfg.ensureDefaultPrinter != null) (ensureDefaultPrinter cfg.ensureDefaultPrinter); }; }; } </ins>

Discussion:
Allow configuration of a cups printer by pointing at a ppd file and specifying a single URL in Currently, such configuration requires clicking through a web-interface. 09
I actually ran into problems with the imperative configuration. I configured my printer (samsung scx3200) and after a system upgrade i was unable to print anymore. An error was shown in the cups web interface for the printer: "unable to load PPD, /nix/store/.... no such file or directory". It looks like the driver i used was garbage-collected. That would not happen with a declarative configuration. However i am certain that this module is no easy piece of work because it requires deep insight into how cups works.
Interestingly for my driver it just copy them to . Does the files within this directory has references to the nix store?
I created a half-stateful solution similar to , which uses etc. to create the configured printers and force them in the right configuration, without having to touch the deep parts of cups. Works quite well, still have to see how it works on printer driver updates, though. Will pose a PR when that succeeds.
PR: please go and test it. :)
Upvote this! Will test on weekend. (looks better, than my own unconditional injection of ppd into /var/.../cups)
Hi, I just stumbled over this issue by accident and realized I'm using something similar in my machines own printing config. So I'm thinking it might help you if I'd share this code with you. Sorry for just dumping this file here. I've been planning to clean it up and suggest my module via a pull-request on its own, but I haven't found the time to do so yet. Still, I hope my module contains some usable ideas towards declarative printer config (e.g. set options, and check that each declared printer has its backend and ppd file installed).