nixos/nix-daemon: use structural settings

The `nix.*` options, apart from options for setting up the
daemon itself, currently provide a lot of setting mappings
for the Nix daemon configuration. The scope of the mapping yields
convience, but the line where an option is considered essential
is blurry. For instance, the `extra-sandbox-paths` mapping is
provided without its primary consumer, and the corresponding
`sandbox-paths` option is also not mapped.

The current system increases the maintenance burden as maintainers have to
closely follow upstream changes. In this case, there are two state versions
of Nix which have to be maintained collectively, with different options
avaliable.

This commit aims to following the standard outlined in RFC 42[1] to
implement a structural setting pattern. The Nix configuration is encoded
at its core as key-value pairs which maps nicely to attribute sets, making
it feasible to express in the Nix language itself. Some existing options are
kept such as `buildMachines` and `registry` which present a simplified interface
to managing the respective settings. The interface is exposed as `nix.settings`.

Legacy configurations are mapped to their corresponding options under `nix.settings`
for backwards compatibility.

Various options settings in other nixos modules and relevant tests have been
updated to use structural setting for consistency.

The generation and validation of the configration file has been modified to
use `writeTextFile` instead of `runCommand` for clarity. Note that validation
is now mandatory as strict checking of options has been pushed down to the
derivation level due to freeformType consuming unmatched options. Furthermore,
validation can not occur when cross-compiling due to current limitations.

A new option `publicHostKey` was added to the `buildMachines`
submodule corresponding to the base64 encoded public host key settings
exposed in the builder syntax. The build machine generation was subsequently
rewritten to use `concatStringsSep` for better performance by grouping
concatenations.

[1] - https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md

10 files changed, 31 insertions, 31 deletions

diff --git a/nixos/tests/containers-imperative.nix b/nixos/tests/containers-imperative.nix
index a126a5480c0..14001657bee 100644
--- a/nixos/tests/containers-imperative.nix
+++ b/nixos/tests/containers-imperative.nix
@@ -10,8 +10,8 @@ import ./make-test-python.nix ({ pkgs, lib, ... }: {
 
       # XXX: Sandbox setup fails while trying to hardlink files from the host's
       #      store file system into the prepared chroot directory.
-      nix.useSandbox = false;
-      nix.binaryCaches = []; # don't try to access cache.nixos.org
+      nix.settings.sandbox = false;
+      nix.settings.substituters = []; # don't try to access cache.nixos.org
 
       virtualisation.writableStore = true;
       # Make sure we always have all the required dependencies for creating a
diff --git a/nixos/tests/hardened.nix b/nixos/tests/hardened.nix
index da7e0972e13..dc455f971f5 100644
--- a/nixos/tests/hardened.nix
+++ b/nixos/tests/hardened.nix
@@ -11,7 +11,7 @@ import ./make-test-python.nix ({ pkgs, ... } : {
       users.users.sybil = { isNormalUser = true; group = "wheel"; };
       imports = [ ../modules/profiles/hardened.nix ];
       environment.memoryAllocator.provider = "graphene-hardened";
-      nix.useSandbox = false;
+      nix.settings.sandbox = false;
       virtualisation.emptyDiskImages = [ 4096 ];
       boot.initrd.postDeviceCommands = ''
         ${pkgs.dosfstools}/bin/mkfs.vfat -n EFISYS /dev/vdb
diff --git a/nixos/tests/hibernate.nix b/nixos/tests/hibernate.nix
index 4f05b99a5a1..3880f1649bd 100644
--- a/nixos/tests/hibernate.nix
+++ b/nixos/tests/hibernate.nix
@@ -45,11 +45,11 @@ in makeTest {
         ../modules/profiles/base.nix
       ];
 
-      nix.binaryCaches = mkForce [ ];
-      nix.extraOptions = ''
-        hashed-mirrors =
-        connect-timeout = 1
-      '';
+      nix.settings = {
+        substituters = mkForce [];
+        hashed-mirrors = null;
+        connect-timeout = 1;
+      };
 
       virtualisation.diskSize = 8 * 1024;
       virtualisation.emptyDiskImages = [
diff --git a/nixos/tests/hydra/common.nix b/nixos/tests/hydra/common.nix
index 1a3a4d8fb3d..fdf2b2c6f6d 100644
--- a/nixos/tests/hydra/common.nix
+++ b/nixos/tests/hydra/common.nix
@@ -42,7 +42,7 @@
         hostName = "localhost";
         systems = [ system ];
       }];
-      binaryCaches = [];
+      settings.substituters = [];
     };
   };
 }
diff --git a/nixos/tests/installer.nix b/nixos/tests/installer.nix
index 7c7eb004e55..761020571fa 100644
--- a/nixos/tests/installer.nix
+++ b/nixos/tests/installer.nix
@@ -334,11 +334,11 @@ let
             (pkgs.grub2_efi.override { inherit zfsSupport; })
           ]);
 
-          nix.binaryCaches = mkForce [ ];
-          nix.extraOptions = ''
-            hashed-mirrors =
-            connect-timeout = 1
-          '';
+          nix.settings = {
+            substituters = mkForce [];
+            hashed-mirrors = null;
+            connect-timeout = 1;
+          };
         };
 
       };
diff --git a/nixos/tests/iscsi-multipath-root.nix b/nixos/tests/iscsi-multipath-root.nix
index a26fea503b6..92ae9990c94 100644
--- a/nixos/tests/iscsi-multipath-root.nix
+++ b/nixos/tests/iscsi-multipath-root.nix
@@ -111,11 +111,11 @@ import ./make-test-python.nix (
 
         environment.etc."initiator-root-disk-closure".source = nodes.initiatorRootDisk.config.system.build.toplevel;
 
-        nix.binaryCaches = lib.mkForce [ ];
-        nix.extraOptions = ''
-          hashed-mirrors =
-          connect-timeout = 1
-        '';
+        nix.settings = {
+          substituters = lib.mkForce [ ];
+          hashed-mirrors = null;
+          connect-timeout = 1;
+        };
       };
 
       initiatorRootDisk = { config, pkgs, modulesPath, lib, ... }: {
diff --git a/nixos/tests/iscsi-root.nix b/nixos/tests/iscsi-root.nix
index bda51d2c2e4..eb0719edc37 100644
--- a/nixos/tests/iscsi-root.nix
+++ b/nixos/tests/iscsi-root.nix
@@ -95,11 +95,11 @@ import ./make-test-python.nix (
 
             system.extraDependencies = [ nodes.initiatorRootDisk.config.system.build.toplevel ];
 
-            nix.binaryCaches = lib.mkForce [];
-            nix.extraOptions = ''
-              hashed-mirrors =
-              connect-timeout = 1
-            '';
+            nix.settings = {
+              substituters = lib.mkForce [];
+              hashed-mirrors = null;
+              connect-timeout = 1;
+            };
           };
 
           initiatorRootDisk = { config, pkgs, modulesPath, lib, ... }: {
diff --git a/nixos/tests/nixops/default.nix b/nixos/tests/nixops/default.nix
index ec3d028aaba..b25fc95f4b3 100644
--- a/nixos/tests/nixops/default.nix
+++ b/nixos/tests/nixops/default.nix
@@ -23,7 +23,7 @@ let
       deployer = { config, lib, nodes, pkgs, ... }: {
         imports = [ ../../modules/installer/cd-dvd/channel.nix ];
         environment.systemPackages = [ nixopsPkg ];
-        nix.binaryCaches = lib.mkForce [ ];
+        nix.settings.substituters = lib.mkForce [ ];
         users.users.person.isNormalUser = true;
         virtualisation.writableStore = true;
         virtualisation.additionalPaths = [
diff --git a/nixos/tests/nixops/legacy/base-configuration.nix b/nixos/tests/nixops/legacy/base-configuration.nix
index dba960f595c..7f1c07a5c4a 100644
--- a/nixos/tests/nixops/legacy/base-configuration.nix
+++ b/nixos/tests/nixops/legacy/base-configuration.nix
@@ -16,7 +16,7 @@ in
     (modulesPath + "/testing/test-instrumentation.nix")
   ];
   virtualisation.writableStore = true;
-  nix.binaryCaches = lib.mkForce [ ];
+  nix.settings.substituters = lib.mkForce [ ];
   virtualisation.graphics = false;
   documentation.enable = false;
   services.qemuGuest.enable = true;
diff --git a/nixos/tests/os-prober.nix b/nixos/tests/os-prober.nix
index c1e29b0f68b..90375450fe1 100644
--- a/nixos/tests/os-prober.nix
+++ b/nixos/tests/os-prober.nix
@@ -43,11 +43,11 @@ let
       # vda is a filesystem without partition table
       forceInstall = true;
     };
-    nix.binaryCaches = lib.mkForce [ ];
-    nix.extraOptions = ''
-      hashed-mirrors =
-      connect-timeout = 1
-    '';
+    nix.settings = {
+      substituters = lib.mkForce [];
+      hashed-mirrors = null;
+      connect-timeout = 1;
+    };
     # save some memory
     documentation.enable = false;
   };