Describe the bug

Derivations defined with pkgs are not compatible with cross compilation as defined in Nixpkgs manual.
This is the case for all derivation defined in NixOS modules.

Steps To Reproduce

Following derivation fails to build, since pkgs is used:

with (import <nixpkgs> { crossSystem.system = "aarch64-linux"; });
runCommand "bad" { nativeBuildInputs = [ jq ]; } "jq > $out"

Following dervation builds, since __splicedPackages is used:

with (import <nixpkgs> { crossSystem.system = "aarch64-linux"; }).__splicedPackages;
runCommand "good" { nativeBuildInputs = [ jq ]; } "jq > $out"

The NixOS module system uses not __splicedPackages and therefor all derivations defined with pkgs which depends on nativeBuildInputs will fail to cross compile.

Workaround

Select the package by hand and do not use stdenv cross compilation automatism:

with (import <nixpkgs> { crossSystem.system = "aarch64-linux"; });
runCommand "workaround" { } "${pkgsBuildBuild.jq}/bin/jq > $out"

Expected behavior

Derivations defined in NixOS modules can be cross compiled.