confusing error while building system configuration using disko as module

[nipsy]

I've been working through enabling disko as a proper flake input which is then consumed as a module on all of my systems. As I'm discovering, that process is not entirely as straightforward as I was expecting.

One example of that is where I'm trying to migrate an existing VirtualBox based VM over to using the previously created disko configuration I'd used originally to install it, but as a standalone file at the time of installation. Now I'm trying to roll the disko configuration into the system configuration directly as a module, and I'm encountering a somewhat bizarre error:

       … while evaluating the attribute 'value'
         at /nix/store/0sxsfzswhjck7f4sbsvznz285s4i7y64-source/lib/modules.nix:614:53:
          613|                 (n: value:
          614|                   [{ inherit (module) file; inherit value; }]
             |                                                     ^
          615|                 )

       … while calling the 'throw' builtin
         at /nix/store/0sxsfzswhjck7f4sbsvznz285s4i7y64-source/nixos/modules/system/activation/top-level.nix:73:10:
           72|   baseSystemAssertWarn = if failedAssertions != []
           73|     then throw "\nFailed assertions:\n${concatStringsSep "\n" (map (x: "- ${x}") failedAssertions)}"
             |          ^
           74|     else showWarnings config.warnings baseSystem;

       error:
       Failed assertions:
       - You cannot have duplicated devices in mirroredBoots

The full error log can be found at https://gist.github.com/nipsy/61652eaf9705093536169f4765e8950c.

What's curious to me about this is I have two almost identical systems. This one if still using legacy boot with the VM configured to support that (BIOS being the default Virtualbox VM configuration) and a separate one with virtually an identical configuration, that is using EFI mode for the VM in Virtualbox, and therefore is also configured to use EFI on the Linux side in NixOS of course.

The current system configuration flake is at https://arrakis.bitgnome.net/nipsy/git/nix/snapshot/nix-master.tar#nixosConfigurations.richese. What's weird to me is that the referenced supposedly duplicated attribute appears to be the same regardless of whether I'm using the configuration with disko enabled as a module:

% nix repl https://arrakis.bitgnome.net/nipsy/git/nix/snapshot/nix-master.tar#nixosConfigurations.richese
Nix 2.24.10
Type :? for help.
Loading installable 'https://arrakis.bitgnome.net/nipsy/git/nix/snapshot/nix-master.tar#nixosConfigurations.richese'...
Added 10 variables.
nix-repl> config.boot.loader.grub.mirroredBoots
[
  { ... }
]

or using the configuration where I've removed disko as a module and gone back to a statically defined set of fileSystems:

% nix repl https://arrakis.bitgnome.net/nipsy/git/nix/snapshot/nix-8d4fc67e4cdf158b29b19d03781aff420b313157.tar#nixosConfigurations.richese
Nix 2.24.10
Type :? for help.
Loading installable 'https://arrakis.bitgnome.net/nipsy/git/nix/snapshot/nix-8d4fc67e4cdf158b29b19d03781aff420b313157.tar#nixosConfigurations.richese'...
Added 10 variables.
nix-repl> config.boot.loader.grub.mirroredBoots
[
  { ... }
]

If I roll back the handful of changes to unmodularize disko for this particular host, then everything works fine again.

The other almost identical system is kaitain. But since it's using EFI, there doesn't appear to be any problem referring to any attribute named mirroredBoots since I'm using systemd-boot and so none of that grub configuration gets pulled in there.

I'm also not using that mirroredBoots attribute anywhere at all in my entire repository, so it can pretty much only be happening as a result of disko, but I'm really unclear as to why.

I also thought initially that it had something to do with the fact I had named my BIOS partition in my disko configuration as boot and my /boot partition as ESP. I tried changing that to simply bios and then later MBR to no avail, so that doesn't seem to be the source of the problem.

Obviously reverting back to the non-disko enabled version of the configuration for this particular host works fine for now. But it would be nice to know if this is simply a bug somewhere or if something else is happening here that I'm not accounting for properly elsewhere in this system's configuration somehow.

[iFreilicht]

I can't download your configuration, unfortunately, I'm getting infinite 301 redirects. Do you have some other way you can share your configuration?

One way to get more information here is to tell the repl explicitly to evaluate the entire attribute and print it with :p:

nix-repl> :p config.boot.loader.grub.mirroredBoots

My assumption is that this will show that the devices array contains two copies of the exact same string. Can you confirm that?

[nipsy]

Sorry about that. My force SSL redirect logic worked fine when I was using separate server blocks in nginx for HTTP and HTTPS. The combined NixOS approach left my redirect logic busted outside my network. Didn't think to test that!

Anyway, you should be able to pull my repo now. Let me know.

[nipsy]

Having said that, you're exactly right (when I use the right tag):

Loading installable 'https://arrakis.bitgnome.net/nipsy/git/nix/snapshot/nix-master.tar#nixosConfigurations.richese'...
Added 10 variables.
nix-repl> :p config.boot.loader.grub.mirroredBoots
[0.4 MiB DL][
  {
    devices = [
      "/dev/sda"
      "/dev/sda"
    ];
    efiBootloaderId = null;
    efiSysMountPoint = "/boot";
    path = "/boot";
  }
]