Change:
<ins> { lib , stdenv , fetchurl , cups , dpkg , gnused , makeWrapper , ghostscript , file , a2ps , coreutils , gnugrep , which , gawk }: let version = "1.1.2"; model = "dcp9020cdw"; in rec { driver = stdenv.mkDerivation { pname = "${model}-lpr"; inherit version; src = fetchurl { url = "https://download.brother.com/welcome/dlf100441/dcp9020cdwlpr-${version}-1.i386.deb"; sha256 = "1z6nma489s0a0b0a8wyg38yxanz4k99dg29fyjs4jlprsvmwk56y"; }; nativeBuildInputs = [ dpkg makeWrapper ]; buildInputs = [ cups ghostscript a2ps gawk ]; unpackPhase = "dpkg-deb -x $src $out"; installPhase = '' substituteInPlace $out/opt/brother/Printers/${model}/lpd/filter${model}  --replace /opt "$out/opt" patchelf --set-interpreter $(cat $NIX_CC/nix-support/dynamic-linker)  $out/opt/brother/Printers/${model}/lpd/br${model}filter mkdir -p $out/lib/cups/filter/ ln -s $out/opt/brother/Printers/${model}/lpd/filter${model} $out/lib/cups/filter/brother_lpdwrapper_${model} wrapProgram $out/opt/brother/Printers/${model}/lpd/filter${model}  --prefix PATH ":" ${lib.makeBinPath [ gawk ghostscript a2ps file gnused gnugrep coreutils which ]} ''; meta = with lib; { homepage = "http://www.brother.com/"; description = "Brother ${model} printer driver"; license = licenses.unfree; platforms = platforms.linux; downloadPage = "https://support.brother.com/g/b/downloadlist.aspx?c=gb&lang=en&prod=${model}_eu&os=128"; maintainers = with maintainers; [ pshirshov ]; }; }; cupswrapper = stdenv.mkDerivation { pname = "${model}-cupswrapper"; inherit version; src = fetchurl { url = "https://download.brother.com/welcome/dlf100443/dcp9020cdwcupswrapper-${version}-1.i386.deb"; sha256 = "04yqm1qv9p4hgp1p6mqq4siygl4056s6flv6kqln8mvmcr8zaq1s"; }; nativeBuildInputs = [ dpkg makeWrapper ]; buildInputs = [ cups ghostscript a2ps gawk ]; unpackPhase = "dpkg-deb -x $src $out"; installPhase = '' for f in $out/opt/brother/Printers/${model}/cupswrapper/cupswrapper${model}; do wrapProgram $f --prefix PATH : ${lib.makeBinPath [ coreutils ghostscript gnugrep gnused ]} done mkdir -p $out/share/cups/model ln -s $out/opt/brother/Printers/${model}/cupswrapper/brother_${model}_printer_en.ppd $out/share/cups/model/ ''; meta = with lib; { homepage = "http://www.brother.com/"; description = "Brother ${model} printer CUPS wrapper driver"; license = licenses.unfree; platforms = platforms.linux; downloadPage = "https://support.brother.com/g/b/downloadlist.aspx?c=gb&lang=en&prod=${model}_eu&os=128"; maintainers = with maintainers; [ pshirshov ]; }; }; } </ins>

Discussion:
CUPSwrapper printer driver for Brother 9020CDW Metadata homepage URL: source URL: license: gpl2 platforms: linux
Well, I've managed to do it on my own, but it would be very nice to have it in the tree. Formula: Put it into and then then add it into
Make a PR?
Have no idea how/where to do it properly
Not sure if I did it right but whatever.
I'm not sure what is wrong with you, though I don't think you have use such rude language. This is my first time when I try to deliver a patch and developers speak with me using imperative-command language. Not sure why you want to be hostile to your users/contributors but good luck with that.
I wasnt being hostile, I just suggested that you could make a pr since youve already packaged it?
I'm talking about your imperative language in the comment to my PR. That doesn't sound nice, sorry.
I don't understand I just told you stuff you needed to know
Of course feedback is needed to improve your PR and get it merged
I didn't mean to be offensive, sorry
Okay, will try.