Recommended style to cross-compile flake nixosSystems

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1

I’m currently tinkering with cross-compiling NixOS from an AMD machine (“x86_64-linux”) to Raspberry Pi 5 (“aarch64-linux”) and Starfive VisionFive 2 (“riscv-linux”), and would like to know about the latest best practice to recommend in guides. I found several similar styles, but i’m not sure which one is the latest and best:

 mySystem = nixpkgs.lib.nixosSystem {
        modules = [
          {
            nixpkgs.buildPlatform = "x86_64-linux";
            nixpkgs.hostPlatform = "riscv64-linux";
          }
        ];
      };

like it seems to be recommended in the official NixOS manual cross-compile section (but unclear as it mentions other styles as well) and in Jörg Thalheims blog post.

 mySystem = nixpkgs.lib.nixosSystem {
        modules = [
          {
            nixpkgs.localSystem.config = "x86_64-unknown-linux-gnu";
            nixpkgs.crossSystem.config = "riscv64-unknown-linux-gnu";
          }
        ];
      };

that seems to be recommended in the official nix.dev cross-compile guide (although that style is shown only for pkgsCross usage)

 mySystem = nixpkgs.lib.nixosSystem {
        modules = [
          {
            nixpkgs.localSystem.system = "x86_64-linux";
            nixpkgs.crossSystem.system = "riscv64-linux";
          }
        ];
      };

that seems to be used in multiple blogs like the fantastic recently published handbook guide by Ryan Yin.

 mySystem = nixpkgs.lib.nixosSystem {
       system = "x86_64-linux"
        modules = [
          {
            nixpkgs.crossSystem.system = "riscv64-linux";
          }
        ];
      };

I have seen this style many times in blog posts.

 mySystem = nixpkgs.lib.nixosSystem {
       system = "x86_64-linux"
        modules = [
          {
            nixpkgs.crossSystem.config = "riscv64-unknown-linux-gnu";
            nixpkgs.crossSystem.system = "riscv64-linux";
          }
        ];
      };

I have sometimes also have seem both system and config having been defined.

So which one is the latest, recommended way? (Or what are the trade-offs?). I could create a PR against the official documentation as well if you can point me to the right place.

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2

Shameless bump as i stumbled upon this part-hilarious blog post https://ianthehenry.com/posts/how-to-learn-nix/cross-compilation/ about the state of the Nix manual on cross-compiling and it describes the same questions and confusion i have. I would like to improve the documentation and start with this low-hanging fruit here.

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