nixos/bcachefs: soft-deprecate 'linuxPackages_testing_bcachefs'

'bcachefs' is included in the linux kernel since 6.7-rc1

nixos/modules/tasks/filesystems/bcachefs.nix

···
     };
   };
 
+  assertions = [
+    {
+      assertion = let
+        kernel = config.boot.kernelPackages.kernel;
+      in (
+        kernel.kernelAtLeast "6.7" || (
+          lib.elem (kernel.structuredExtraConfig.BCACHEFS_FS or null) [
+            lib.kernel.module
+            lib.kernel.yes
+            lib.kernel.option.yes
+          ]
+        )
+      );
+
+      message = "Linux 6.7-rc1 at minimum or a custom linux kernel with bcachefs support is required";
+    }
+  ];
 in
 
 {
   config = lib.mkIf (lib.elem "bcachefs" config.boot.supportedFilesystems) (lib.mkMerge [
     {
+      inherit assertions;
       # needed for systemd-remount-fs
       system.fsPackages = [ pkgs.bcachefs-tools ];
 
-      # use kernel package with bcachefs support until it's in mainline
-      # TODO replace with requireKernelConfig
-      boot.kernelPackages = pkgs.linuxPackages_testing_bcachefs;
+      # FIXME: Replace this with `linuxPackages_testing` after NixOS 23.11 is released
+      # FIXME: Replace this with `linuxPackages_latest` when 6.7 is released, remove this line when the LTS version is at least 6.7
+      boot.kernelPackages = lib.mkDefault (
+        # FIXME: Remove warning after NixOS 23.11 is released
+        lib.warn "Please upgrade to Linux 6.7-rc1 or later: 'linuxPackages_testing_bcachefs' is deprecated. Use 'boot.kernelPackages = pkgs.linuxPackages_testing;' to silence this warning"
+        pkgs.linuxPackages_testing_bcachefs
+      );
 
       systemd.services = lib.mapAttrs' (mkUnits "") (lib.filterAttrs (n: fs: (fs.fsType == "bcachefs") && (!utils.fsNeededForBoot fs)) config.fileSystems);
     }
 
     (lib.mkIf ((lib.elem "bcachefs" config.boot.initrd.supportedFilesystems) || (bootFs != {})) {
+      inherit assertions;
       # chacha20 and poly1305 are required only for decryption attempts
       boot.initrd.availableKernelModules = [ "bcachefs" "sha256" "chacha20" "poly1305" ];
       boot.initrd.systemd.extraBin = {

pkgs/top-level/all-packages.nix

···
   linuxPackages_testing = linuxKernel.packages.linux_testing;
   linux_testing = linuxKernel.kernels.linux_testing;
 
+  # FIXME: Remove and alias to `linux(Packages)_testing`` after 23.11 is released
   linuxPackages_testing_bcachefs = linuxKernel.packages.linux_testing_bcachefs;
   linux_testing_bcachefs = linuxKernel.kernels.linux_testing_bcachefs;
 

pkgs/top-level/linux-kernels.nix

···
        then latest
        else testing;
 
+    # FIXME: Remove after 23.11 is released
     linux_testing_bcachefs = callPackage ../os-specific/linux/kernel/linux-testing-bcachefs.nix {
       # Pinned on the last version which Kent's commits can be cleany rebased up.
       kernel = linux_6_5;
···
 
     # Intentionally lacks recurseIntoAttrs, as -rc kernels will quite likely break out-of-tree modules and cause failed Hydra builds.
     linux_testing = packagesFor kernels.linux_testing;
+    # FIXME: Remove after 23.11 is released
     linux_testing_bcachefs = recurseIntoAttrs (packagesFor kernels.linux_testing_bcachefs);
 
     linux_hardened = recurseIntoAttrs (packagesFor kernels.linux_hardened);