anchor.diff:  # often change with updating of git or cgit.
   # stripLen acts as the -p parameter when applying a patch.
   
  -{ lib, fetchurl, patchutils }:
  +{ lib, fetchurl, buildPackages }:
   { stripLen ? 0, extraPrefix ? null, excludes ? [], includes ? [], revert ? false, ... }@args:
   
   fetchurl ({
  
positive.code:       echo "error: Fetched patch file '$out' is empty!" 1>&2
        exit 1
      fi
      "${patchutils}/bin/lsdiff" "$out" \
        | sort -u | sed -e 's/[*?]/\\&/g' \
        | xargs -I{} \
          "${patchutils}/bin/filterdiff" \
          --include={} \
          --strip=${toString stripLen} \
          ${lib.optionalString (extraPrefix != null) ''
  
negative.code:       cat "$out" 1>&2
        exit 1
      fi
      ${buildPackages.patchutils}/bin/filterdiff \
        -p1 \
        ${builtins.toString (builtins.map (x: "-x ${lib.escapeShellArg x}") excludes)} \
        ${builtins.toString (builtins.map (x: "-i ${lib.escapeShellArg x}") includes)} \
  