1 files changed, 75 insertions, 34 deletions
diff --git a/nixos/modules/system/activation/switchable-system.nix b/nixos/modules/system/activation/switchable-system.nix
index d5bd8cc1dc115..d70fefd0920b4 100644
--- a/nixos/modules/system/activation/switchable-system.nix
+++ b/nixos/modules/system/activation/switchable-system.nix
@@ -4,52 +4,93 @@ let
 
   perlWrapped = pkgs.perl.withPackages (p: with p; [ ConfigIniFiles FileSlurp ]);
 
+  description = extra: ''
+    Whether to include the capability to switch configurations.
+
+    Disabling this makes the system unable to be reconfigured via `nixos-rebuild`.
+
+    ${extra}
+  '';
+
 in
 
 {
 
-  options = {
-    system.switch.enable = lib.mkOption {
+  options.system.switch = {
+    enable = lib.mkOption {
       type = lib.types.bool;
       default = true;
-      description = ''
-        Whether to include the capability to switch configurations.
-
-        Disabling this makes the system unable to be reconfigured via `nixos-rebuild`.
-
+      description = description ''
         This is good for image based appliances where updates are handled
         outside the image. Reducing features makes the image lighter and
         slightly more secure.
       '';
     };
-  };
 
-  config = lib.mkIf config.system.switch.enable {
-    system.activatableSystemBuilderCommands = ''
-      mkdir $out/bin
-      substitute ${./switch-to-configuration.pl} $out/bin/switch-to-configuration \
-        --subst-var out \
-        --subst-var-by toplevel ''${!toplevelVar} \
-        --subst-var-by coreutils "${pkgs.coreutils}" \
-        --subst-var-by distroId ${lib.escapeShellArg config.system.nixos.distroId} \
-        --subst-var-by installBootLoader ${lib.escapeShellArg config.system.build.installBootLoader} \
-        --subst-var-by localeArchive "${config.i18n.glibcLocales}/lib/locale/locale-archive" \
-        --subst-var-by perl "${perlWrapped}" \
-        --subst-var-by shell "${pkgs.bash}/bin/sh" \
-        --subst-var-by su "${pkgs.shadow.su}/bin/su" \
-        --subst-var-by systemd "${config.systemd.package}" \
-        --subst-var-by utillinux "${pkgs.util-linux}" \
-        ;
-
-      chmod +x $out/bin/switch-to-configuration
-      ${lib.optionalString (pkgs.stdenv.hostPlatform == pkgs.stdenv.buildPlatform) ''
-        if ! output=$(${perlWrapped}/bin/perl -c $out/bin/switch-to-configuration 2>&1); then
-          echo "switch-to-configuration syntax is not valid:"
-          echo "$output"
-          exit 1
-        fi
-      ''}
-    '';
+    enableNg = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = description ''
+        Whether to use `switch-to-configuration-ng`, an experimental
+        re-implementation of `switch-to-configuration` with the goal of
+        replacing the original.
+      '';
+    };
   };
 
+  config = lib.mkMerge [
+    {
+      assertions = [{
+        assertion = with config.system.switch; enable -> !enableNg;
+        message = "Only one of system.switch.enable and system.switch.enableNg may be enabled at a time";
+      }];
+    }
+    (lib.mkIf config.system.switch.enable {
+      system.activatableSystemBuilderCommands = ''
+        mkdir $out/bin
+        substitute ${./switch-to-configuration.pl} $out/bin/switch-to-configuration \
+          --subst-var out \
+          --subst-var-by toplevel ''${!toplevelVar} \
+          --subst-var-by coreutils "${pkgs.coreutils}" \
+          --subst-var-by distroId ${lib.escapeShellArg config.system.nixos.distroId} \
+          --subst-var-by installBootLoader ${lib.escapeShellArg config.system.build.installBootLoader} \
+          --subst-var-by localeArchive "${config.i18n.glibcLocales}/lib/locale/locale-archive" \
+          --subst-var-by perl "${perlWrapped}" \
+          --subst-var-by shell "${pkgs.bash}/bin/sh" \
+          --subst-var-by su "${pkgs.shadow.su}/bin/su" \
+          --subst-var-by systemd "${config.systemd.package}" \
+          --subst-var-by utillinux "${pkgs.util-linux}" \
+          ;
+
+        chmod +x $out/bin/switch-to-configuration
+        ${lib.optionalString (pkgs.stdenv.hostPlatform == pkgs.stdenv.buildPlatform) ''
+          if ! output=$(${perlWrapped}/bin/perl -c $out/bin/switch-to-configuration 2>&1); then
+            echo "switch-to-configuration syntax is not valid:"
+            echo "$output"
+            exit 1
+          fi
+        ''}
+      '';
+    })
+    (lib.mkIf config.system.switch.enableNg {
+      # Use a subshell so we can source makeWrapper's setup hook without
+      # affecting the rest of activatableSystemBuilderCommands.
+      system.activatableSystemBuilderCommands = ''
+        (
+          source ${pkgs.buildPackages.makeWrapper}/nix-support/setup-hook
+
+          mkdir $out/bin
+          ln -sf ${lib.getExe pkgs.switch-to-configuration-ng} $out/bin/switch-to-configuration
+          wrapProgram $out/bin/switch-to-configuration \
+            --set OUT $out \
+            --set TOPLEVEL ''${!toplevelVar} \
+            --set DISTRO_ID ${lib.escapeShellArg config.system.nixos.distroId} \
+            --set INSTALL_BOOTLOADER ${lib.escapeShellArg config.system.build.installBootLoader} \
+            --set LOCALE_ARCHIVE ${config.i18n.glibcLocales}/lib/locale/locale-archive \
+            --set SYSTEMD ${config.systemd.package}
+        )
+      '';
+    })
+  ];
+
 }