nixos/bootspec: adopt the merged RFC-0125

This removes the feature preview warning, enable by default bootspec,
adds a validation flag to prevent Go to go into build-time closure.

This will break all downstream users of bootspec as those changes are
not backward-compatible.

nixos/doc/manual/release-notes/rl-2305.section.md

···
 
 - `libxcrypt`, the library providing the `crypt(3)` password hashing function, is now built without support for algorithms not flagged [`strong`](https://github.com/besser82/libxcrypt/blob/v4.4.33/lib/hashes.conf#L48). This affects the availability of password hashing algorithms used for system login (`login(1)`, `passwd(1)`), but also Apache2 Basic-Auth, Samba, OpenLDAP, Dovecot, and [many other packages](https://github.com/search?q=repo%3ANixOS%2Fnixpkgs%20libxcrypt&type=code).
 
+- `boot.bootspec.enable` (internal option) is now enabled by default because [RFC-0125](https://github.com/NixOS/rfcs/pull/125) was merged. This means you will have a bootspec document called `boot.json` generated for each system and specialisation in the top-level. This is useful to enable advanced boot usecases in NixOS such as SecureBoot.
+
 ## New Services {#sec-release-23.05-new-services}
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->

nixos/modules/system/activation/bootspec.cue

···
-#V1: {
+import "struct"
+
+#BootspecV1: {
 	system:         string
 	init:           string
 	initrd?:        string
···
 	kernelParams: [...string]
 	label:    string
 	toplevel: string
-	specialisation?: {
-		[=~"^"]: #V1
-	}
-	extensions?: {...}
+}
+
+// A restricted document does not allow any official specialisation
+// information in it to avoid "recursive specialisations".
+#RestrictedDocument: struct.MinFields(1) & {
+	"org.nixos.bootspec.v1": #BootspecV1
+	[=~"^"]:                 #BootspecExtension
 }
 
-Document: {
-	v1: #V1
+// Specialisations are a hashmap of strings
+#BootspecSpecialisationV1: [string]: #RestrictedDocument
+
+// Bootspec extensions are defined by the extension author.
+#BootspecExtension: {...}
+
+// A "full" document allows official specialisation information
+// in the top-level with a reserved namespaced key.
+Document: #RestrictedDocument & {
+	"org.nixos.specialisation.v1"?: #BootspecSpecialisationV1
 }

nixos/modules/system/activation/bootspec.nix

···
       filename = "boot.json";
       json =
         pkgs.writeText filename
-          (builtins.toJSON
+        (builtins.toJSON
+          # Merge extensions first to not let them shadow NixOS bootspec data.
+          (cfg.extensions //
           {
-            v1 = {
+            "org.nixos.bootspec.v1" = {
               system = config.boot.kernelPackages.stdenv.hostPlatform.system;
               kernel = "${config.boot.kernelPackages.kernel}/${config.system.boot.loader.kernelFile}";
               kernelParams = config.boot.kernelParams;
               label = "${config.system.nixos.distroName} ${config.system.nixos.codeName} ${config.system.nixos.label} (Linux ${config.boot.kernelPackages.kernel.modDirVersion})";
-
-              inherit (cfg) extensions;
             } // lib.optionalAttrs config.boot.initrd.enable {
               initrd = "${config.system.build.initialRamdisk}/${config.system.boot.loader.initrdFile}";
               initrdSecrets = "${config.system.build.initialRamdiskSecretAppender}/bin/append-initrd-secrets";
             };
-          });
+          }));
 
       generator =
         let
···
           toplevelInjector = lib.escapeShellArgs [
             "${pkgs.jq}/bin/jq"
             ''
-              .v1.toplevel = $toplevel |
-              .v1.init = $init
+              ."org.nixos.bootspec.v1".toplevel = $toplevel |
+              ."org.nixos.bootspec.v1".init = $init
             ''
             "--sort-keys"
             "--arg" "toplevel" "${placeholder "out"}"
···
             lib.escapeShellArgs [
               "${pkgs.jq}/bin/jq"
               "--sort-keys"
-              ".v1.specialisation = ($ARGS.named | map_values(. | first | .v1))"
+              ''."org.nixos.specialisation.v1" = ($ARGS.named | map_values(. | first))''
             ] + " ${lib.concatStringsSep " " specialisationLoader}";
         in
-        ''
-          mkdir -p $out/bootspec
-
-          ${toplevelInjector} | ${specialisationInjector} > $out/${filename}
-        '';
+        "${toplevelInjector} | ${specialisationInjector} > $out/${filename}";
 
       validator = pkgs.writeCueValidator ./bootspec.cue {
         document = "Document"; # Universal validator for any version as long the schema is correctly set.
···
 in
 {
   options.boot.bootspec = {
-    enable = lib.mkEnableOption (lib.mdDoc "Enable generation of RFC-0125 bootspec in $system/bootspec, e.g. /run/current-system/bootspec");
+    enable = lib.mkEnableOption (lib.mdDoc "the generation of RFC-0125 bootspec in $system/boot.json, e.g. /run/current-system/boot.json")
+      // { default = true; internal = true; };
+    enableValidation = lib.mkEnableOption (lib.mdDoc ''the validation of bootspec documents for each build.
+      This will introduce Go in the build-time closure as we are relying on [Cuelang](https://cuelang.org/) for schema validation.
+      Enable this option if you want to ascertain that your documents are correct.
+      ''
+    );
 
     extensions = lib.mkOption {
-      type = lib.types.attrsOf lib.types.attrs; # <namespace>: { ...namespace-specific fields }
+      # NOTE(RaitoBezarius): this is not enough to validate: extensions."osRelease" = drv; those are picked up by cue validation.
+      type = lib.types.attrsOf lib.types.anything; # <namespace>: { ...namespace-specific fields }
       default = { };
       description = lib.mdDoc ''
         User-defined data that extends the bootspec document.
···
       internal = true;
       default = schemas.v1.filename;
     };
-  };
-
-  config = lib.mkIf (cfg.enable) {
-    warnings = [
-      ''RFC-0125 is not merged yet, this is a feature preview of bootspec.
-        The schema is not definitive and features are not guaranteed to be stable until RFC-0125 is merged.
-        See:
-        - https://github.com/NixOS/nixpkgs/pull/172237 to track merge status in nixpkgs.
-        - https://github.com/NixOS/rfcs/pull/125 to track RFC status.
-      ''
-    ];
   };
 }

nixos/modules/system/activation/top-level.nix

···
 
       ${optionalString (!config.boot.isContainer && config.boot.bootspec.enable) ''
         ${config.boot.bootspec.writer}
-        ${config.boot.bootspec.validator} "$out/${config.boot.bootspec.filename}"
+        ${optionalString config.boot.bootspec.enableValidation
+          ''${config.boot.bootspec.validator} "$out/${config.boot.bootspec.filename}"''}
       ''}
 
       ${config.system.extraSystemBuilderCmds}

nixos/tests/bootspec.nix

···
 
       machine.succeed("test -e /run/current-system/boot.json")
 
-      bootspec = json.loads(machine.succeed("jq -r '.v1' /run/current-system/boot.json"))
+      bootspec = json.loads(machine.succeed("jq -r '.\"org.nixos.bootspec.v1\"' /run/current-system/boot.json"))
 
       assert all(key in bootspec for key in ('initrd', 'initrdSecrets')), "Bootspec should contain initrd or initrdSecrets field when initrd is enabled"
     '';
···
       machine.succeed("test -e /run/current-system/boot.json")
       machine.succeed("test -e /run/current-system/specialisation/something/boot.json")
 
-      sp_in_parent = json.loads(machine.succeed("jq -r '.v1.specialisation.something' /run/current-system/boot.json"))
+      sp_in_parent = json.loads(machine.succeed("jq -r '.\"org.nixos.specialisation.v1\".something' /run/current-system/boot.json"))
       sp_in_fs = json.loads(machine.succeed("cat /run/current-system/specialisation/something/boot.json"))
 
-      assert sp_in_parent == sp_in_fs['v1'], "Bootspecs of the same specialisation are different!"
+      assert sp_in_parent['org.nixos.bootspec.v1'] == sp_in_fs['org.nixos.bootspec.v1'], "Bootspecs of the same specialisation are different!"
     '';
   };
 
···
       imports = [ standard ];
       environment.systemPackages = [ pkgs.jq ];
       boot.bootspec.extensions = {
-        osRelease = config.environment.etc."os-release".source;
+        "org.nix-tests.product" = {
+          osRelease = config.environment.etc."os-release".source;
+        };
       };
     };
 
···
       machine.wait_for_unit("multi-user.target")
 
       current_os_release = machine.succeed("cat /etc/os-release")
-      bootspec_os_release = machine.succeed("cat $(jq -r '.v1.extensions.osRelease' /run/current-system/boot.json)")
+      bootspec_os_release = machine.succeed("cat $(jq -r '.\"org.nix-tests.product\".osRelease' /run/current-system/boot.json)")
 
       assert current_os_release == bootspec_os_release, "Filename referenced by extension has unexpected contents"
     '';