@roberth @mweinelt @dasJ @Ma27 Could you review, please?

@roberth I'm not sure about new commit, but it's work for me.

Passes installer test.

Thanks!

This breaks things for cross-compiled installer images.

@tpwrules what things? If you want the problem to be solved, you'll have to be more specific.

My apologies. This causes nixpkgs.hostPlatform to be set to the system type where the installer image was built instead of the system type where nixos-generate-config was run. Therefore, on a fresh install, nixpkgs is evaluated for the wrong system and the install fails.

I'm not sure whether reverting this commit is the right option or if there's a better source to fill in this field in a hard-coded manner.

@tpwrules The file containing the nixpkgs.hostPlatform definition is documented as follows

/etc/nixos/hardware-configuration.nix
This module sets NixOS configuration options based on your current hardware configuration.

My reasoning for using hostPlatform directly, is that nixos-generate-config is meant to run on the host* hardware.
So far so good, but how does nixos-generate-config even run on the final hardware? I've assumed that you would cross compile nixos-generate-config, because otherwise it can't run on the final hardware.

The previous behavior was to pull from builtins.currentSystem aka the system option in nix.conf or whatever Nix itself was built with. I would expect that value to coincide with hostPlatform as well. So I'm skeptical that reverting this PR would fix your problem.

if there's a better source to fill in this field in a hard-coded manner.

I'm not aware of a better source than eval-time hostPlatform which is generally equal to the runtime nix system on the host, including on a cross compiled installer image (I would surely expect).

You mention an installer image. Where did that image come from? Maybe something is wrong about the image?

Or maybe it should be made a bit more clear that you're not supposed to use a hardware-configuration.nix generated on one machine for the configuration of a different machine. It kind of seems like that's what you're doing, and it wouldn't work well for other reasons, like wrong file system labels and driver modules.

* (perhaps superfluously) host from the GNU terminology: build is where the build is performed, host is where the output of the build runs, target is irrelevant because a NixOS configuration is not a compiler we're compiling.

I publish my own cross-compiled installer images here. They are designed to be cross-compiled from x86_64-linux to aarch64-linux (or built natively on aarch64-linux). When the cross-compiled image is booted on the aarch64-linux device and nixos-generate-config is run from that image on that device, it puts nixpkgs.hostPlatform = "x86_64-linux"; into hardware-configuration.nix and the system does not build. It is absolutely not the case that hardware-configuration.nix is being moved between systems.

Using the linked commit on an x86_64-linux system:

$ nix eval .#installer-bootstrap.config.system.build.nixos-generate-config.stdenv.hostPlatform.system
"aarch64-linux"

$ nix eval .#installer-bootstrap.config.system.build.nixos-generate-config.system
"x86_64-linux"

$ nix build .#installer-bootstrap.config.system.build.nixos-generate-config

$ cat result/bin/nixos-generate-config | grep hostPlatform
push @attrs, "nixpkgs.hostPlatform = lib.mkDefault \"x86_64-linux\";";

You are right that hostPlatform is the right attribute and I did have a misconception about the terminology. But there is something wrong and the wrong hostPlatform is clearly being substituted even though the cross-compiled image builds and boots successfully and has for many months, including before this commit. It's not immediately clear to me what the issue is and if it's the fault of my configuration. Do you have any ideas?

#237218 should fix it. Could you give it a try?