Hello everybody!
It is quite common to build packages in a flake for several systems:
{
# […]
outputs = { self, nixpkgs }:
let
supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });
in {
packages = forAllSystems (system:
let
pkgs = nixpkgsFor.${system};
in {
package_1 = {…};
package_2 = {…};
# […]
});
};
}
My question is: How would you add another package, lets say package_3 for only one of the systems in the list supportedSystem? Just updating it with // like this does not work:
# […]
packages = forAllSystems (system:
let
pkgs = nixpkgsFor.${system};
in {
package_1 = {…};
package_2 = {…};
# […]
}) // {
"x86_64-linux" = {
package_3 = {};
};
};
# […]
I tested that with playing in the nix repl:
packages = {"linux" = {"app_1" = {}; "app_2" = {};}; "osx" = {"app_1" = {}; "app_2" = {};};}
(packages // {"linux" = {"app_3" = {};};})."linux"
The reason is that it would then absolutely override the whole attribute x86_64-linux in the first argument of the //-operand. So some kind of a recursive // would be nice.
I am aware of https://stackoverflow.com/a/54505212 where the author self-defines a function for this. However I wonder if there is no dedicated library-function present for this. That would be surprising as you would expect this to be quite a common case that some of your packages are architecture-dependend and may not exist for every architecture or for just one of them.
