zfs-latest: fix eval errors

nixosModules/installer/zfs-latest.nix

@@ -12,8 +12,14 @@ let
     (builtins.match "linux_[0-9]+_[0-9]+" name) != null
     && (builtins.tryEval kernelPackages).success
     && (
-      (!isUnstable && !kernelPackages.zfs.meta.broken)
-      || (isUnstable && !kernelPackages.zfs_unstable.meta.broken)
+      let
+        zfsPackage =
+          if isUnstable then
+            kernelPackages.zfs_unstable
+          else
+            kernelPackages.${pkgs.zfs.kernelModuleAttribute};
+      in
+      !(zfsPackage.meta.broken or false)
     )
   ) pkgs.linuxKernel.packages;
   latestKernelPackage = lib.last (
@@ -24,5 +30,5 @@ let
 in
 {
   # Note this might jump back and worth as kernel get added or removed.
-  boot.kernelPackages = latestKernelPackage;
+  boot.kernelPackages = lib.mkIf (lib.meta.availableOn pkgs.hostPlatform pkgs.zfs) latestKernelPackage;
 }