systemd-stage-1: Add assertions for unsupported options.

nixos/modules/services/hardware/udev.nix

···
 
     boot.kernelParams = mkIf (!config.networking.usePredictableInterfaceNames) [ "net.ifnames=0" ];
 
-    boot.initrd.extraUdevRulesCommands = optionalString (!config.boot.initrd.systemd.enable && config.boot.initrd.services.udev.rules != "")
+    boot.initrd.extraUdevRulesCommands = mkIf (!config.boot.initrd.systemd.enable && config.boot.initrd.services.udev.rules != "")
       ''
         cat <<'EOF' > $out/99-local.rules
         ${config.boot.initrd.services.udev.rules}

nixos/modules/services/networking/multipath.nix

···
     # We do not have systemd in stage-1 boot so must invoke `multipathd`
     # with the `-1` argument which disables systemd calls. Invoke `multipath`
     # to display the multipath mappings in the output of `journalctl -b`.
+    # TODO: Implement for systemd stage 1
     boot.initrd.kernelModules = [ "dm-multipath" "dm-service-time" ];
-    boot.initrd.postDeviceCommands = ''
+    boot.initrd.postDeviceCommands = mkIf (!config.boot.initrd.systemd.enable) ''
       modprobe -a dm-multipath dm-service-time
       multipathd -s
       (set -x && sleep 1 && multipath -ll)

nixos/modules/system/boot/initrd-network.nix

···
 
     boot.initrd.kernelModules = [ "af_packet" ];
 
-    boot.initrd.extraUtilsCommands = ''
+    boot.initrd.extraUtilsCommands = mkIf (!config.boot.initrd.systemd.enable) ''
       copy_bin_and_libs ${pkgs.klibc}/lib/klibc/bin.static/ipconfig
     '';
 
-    boot.initrd.preLVMCommands = mkBefore (
+    boot.initrd.preLVMCommands = mkIf (!config.boot.initrd.systemd.enable) (mkBefore (
       # Search for interface definitions in command line.
       ''
         ifaces=""
···
         done
       ''
 
-      + cfg.postCommands);
+      + cfg.postCommands));
 
-    boot.initrd.postMountCommands = mkIf cfg.flushBeforeStage2 ''
+    boot.initrd.postMountCommands = mkIf (cfg.flushBeforeStage2 && !config.boot.initrd.systemd.enable) ''
       for iface in $ifaces; do
         ip address flush dev "$iface"
         ip link set dev "$iface" down

nixos/modules/system/boot/systemd/initrd.nix

···
   };
 
   config = mkIf (config.boot.initrd.enable && cfg.enable) {
+    assertions = map (name: {
+      assertion = lib.attrByPath name (throw "impossible") config.boot.initrd == "";
+      message = ''
+        systemd stage 1 does not support 'boot.initrd.${lib.concatStringsSep "." name}'. Please
+          convert it to analogous systemd units in 'boot.initrd.systemd'.
+
+            Definitions:
+        ${lib.concatMapStringsSep "\n" ({ file, ... }: "    - ${file}") (lib.attrByPath name (throw "impossible") options.boot.initrd).definitionsWithLocations}
+      '';
+    }) [
+      [ "preFailCommands" ]
+      [ "preDeviceCommands" ]
+      [ "preLVMCommands" ]
+      [ "postDeviceCommands" ]
+      [ "postMountCommands" ]
+      [ "extraUdevRulesCommands" ]
+      [ "extraUtilsCommands" ]
+      [ "extraUtilsCommandsTest" ]
+      [ "network" "postCommands" ]
+    ];
+
     system.build = { inherit initialRamdisk; };
 
     boot.initrd.availableKernelModules = [

nixos/modules/tasks/encrypted-devices.nix

···
           }) earlyEncDevs);
         forceLuksSupportInInitrd = true;
       };
-      postMountCommands =
-        concatMapStrings (dev:
+      # TODO: systemd stage 1
+      postMountCommands = lib.mkIf (!config.boot.initrd.systemd.enable)
+        (concatMapStrings (dev:
           "cryptsetup luksOpen --key-file ${dev.encrypted.keyFile} ${dev.encrypted.blkDev} ${dev.encrypted.label};\n"
-        ) lateEncDevs;
+        ) lateEncDevs);
     };
   };
 }

nixos/modules/tasks/filesystems/bcachefs.nix

···
         copy_bin_and_libs ${pkgs.bcachefs-tools}/bin/bcachefs
         copy_bin_and_libs ${mountCommand}/bin/mount.bcachefs
       '';
-      boot.initrd.extraUtilsCommandsTest = ''
+      boot.initrd.extraUtilsCommandsTest = lib.mkIf (!config.boot.initrd.systemd.enable) ''
         $out/bin/bcachefs version
       '';
 
-      boot.initrd.postDeviceCommands = commonFunctions + concatStrings (mapAttrsToList openCommand bootFs);
+      boot.initrd.postDeviceCommands = lib.mkIf (!config.boot.initrd.systemd.enable) (commonFunctions + concatStrings (mapAttrsToList openCommand bootFs));
 
       boot.initrd.systemd.services = lib.mapAttrs' (mkUnits "/sysroot") bootFs;
     })

nixos/modules/tasks/filesystems/zfs.nix

···
       boot.initrd = mkIf inInitrd {
         kernelModules = [ "zfs" ] ++ optional (!cfgZfs.enableUnstable) "spl";
         extraUtilsCommands =
-          ''
+          mkIf (!config.boot.initrd.systemd.enable) ''
             copy_bin_and_libs ${cfgZfs.package}/sbin/zfs
             copy_bin_and_libs ${cfgZfs.package}/sbin/zdb
             copy_bin_and_libs ${cfgZfs.package}/sbin/zpool
           '';
-        extraUtilsCommandsTest = mkIf inInitrd
-          ''
+        extraUtilsCommandsTest =
+          mkIf (!config.boot.initrd.systemd.enable) ''
             $out/bin/zfs --help >/dev/null 2>&1
             $out/bin/zpool --help >/dev/null 2>&1
           '';
-        postDeviceCommands = concatStringsSep "\n" ([''
+        postDeviceCommands = mkIf (!config.boot.initrd.systemd.enable) (concatStringsSep "\n" ([''
             ZFS_FORCE="${optionalString cfgZfs.forceImportRoot "-f"}"
           ''] ++ [(importLib {
             # See comments at importLib definition.
···
               else concatMapStrings (fs: ''
                 zfs load-key -- ${escapeShellArg fs}
               '') (filter (x: datasetToPool x == pool) cfgZfs.requestEncryptionCredentials)}
-        '') rootPools));
+        '') rootPools)));
 
         # Systemd in stage 1
-        systemd = {
+        systemd = mkIf config.boot.initrd.systemd.enable {
           packages = [cfgZfs.package];
           services = listToAttrs (map (pool: createImportService {
             inherit pool;

nixos/modules/tasks/swraid.nix

···
         cp -v ${pkgs.mdadm}/lib/udev/rules.d/*.rules $out/
       '';
 
-      extraUtilsCommands = ''
+      extraUtilsCommands = lib.mkIf (!config.boot.initrd.systemd.enable) ''
         # Add RAID mdadm tool.
         copy_bin_and_libs ${pkgs.mdadm}/sbin/mdadm
         copy_bin_and_libs ${pkgs.mdadm}/sbin/mdmon
       '';
 
-      extraUtilsCommandsTest = ''
+      extraUtilsCommandsTest = lib.mkIf (!config.boot.initrd.systemd.enable) ''
         $out/bin/mdadm --version
       '';
 

nixos/tests/common/auto-format-root-device.nix

···
 # `virtualisation.fileSystems."/".autoFormat = true;`
 # instead.
 
-{ config, pkgs, ... }:
+{ lib, config, pkgs, ... }:
 
 let
   rootDevice = config.virtualisation.rootDevice;
 in
 {
 
-  boot.initrd.extraUtilsCommands = ''
+  boot.initrd.extraUtilsCommands = lib.mkIf (!config.boot.initrd.systemd.enable) ''
     # We need mke2fs in the initrd.
     copy_bin_and_libs ${pkgs.e2fsprogs}/bin/mke2fs
   '';
 
-  boot.initrd.postDeviceCommands = ''
+  boot.initrd.postDeviceCommands = lib.mkIf (!config.boot.initrd.systemd.enable) ''
     # If the disk image appears to be empty, run mke2fs to
     # initialise.
     FSTYPE=$(blkid -o value -s TYPE ${rootDevice} || true)