refactor CI and remote builders

hosts/build03/builders.nix

@@ -6,27 +6,21 @@ in
   sops.secrets.id_buildfarm = { };
 
   nix.distributedBuilds = true;
-  nix.buildMachines = [
-    {
-      hostName = "build04.nix-community.org";
-      maxJobs = 80;
-      protocol = "ssh-ng";
-      sshKey = config.sops.secrets.id_buildfarm.path;
-      sshUser = "nix";
-      systems = [ "aarch64-linux" ];
-      supportedFeatures = nixosConfigurations.build04.config.nix.settings.system-features;
-    }
-    {
-      hostName = "darwin02.nix-community.org";
-      maxJobs = 8;
-      protocol = "ssh-ng";
-      sshKey = config.sops.secrets.id_buildfarm.path;
-      sshUser = "nix";
-      systems = [
-        "aarch64-darwin"
-        "x86_64-darwin"
+  nix.buildMachines =
+    map
+      (x: {
+        hostName = "${x.config.networking.hostName}.nix-community.org";
+        maxJobs = x.config.nix.settings.max-jobs;
+        protocol = "ssh-ng";
+        sshKey = config.sops.secrets.id_buildfarm.path;
+        sshUser = "nix";
+        systems = [
+          x.config.nixpkgs.hostPlatform.system
+        ] ++ (x.config.nix.settings.extra-platforms or [ ]);
+        supportedFeatures = x.config.nix.settings.system-features;
+      })
+      [
+        darwinConfigurations.darwin02
+        nixosConfigurations.build04
       ];
-      supportedFeatures = darwinConfigurations.darwin02.config.nix.settings.system-features;
-    }
-  ];
 }

modules/nixos/buildbot.nix

@@ -3,6 +3,14 @@
   inputs,
   ...
 }:
+let
+  buildSystems =
+    [
+      config.nixpkgs.hostPlatform.system
+    ]
+    ++ config.nix.settings.extra-platforms
+    ++ builtins.concatLists (map (host: host.systems) config.nix.buildMachines);
+in
 {
   imports = [
     inputs.buildbot-nix.nixosModules.buildbot-master
@@ -25,12 +33,7 @@
       "zimbatm"
       "zowoq"
     ];
-    buildSystems = [
-      "x86_64-linux"
-      "aarch64-linux"
-      "x86_64-darwin"
-      "aarch64-darwin"
-    ];
+    inherit buildSystems;
     domain = "buildbot.nix-community.org";
     outputsPath = "/var/www/buildbot/nix-outputs/";
     evalMaxMemorySize = 4096;

modules/nixos/common/builder.nix

@@ -19,10 +19,6 @@
       script = builtins.readFile "${inputs.self}/modules/shared/free-space.bash";
     };
 
-    nixpkgs.hostPlatform = {
-      inherit (pkgs.hostPlatform) system;
-    };
-
     nix.settings.extra-platforms = lib.mkIf (config.nixpkgs.hostPlatform.system == "x86_64-linux") [
       (lib.mkIf (config.boot.binfmt.emulatedSystems == [ ]) "i686-linux")
       "x86_64-v1-linux"

modules/nixos/hydra.nix

@@ -1,4 +1,16 @@
-{ pkgs, config, ... }:
+{
+  pkgs,
+  config,
+  lib,
+  ...
+}:
+let
+  inherit (lib) concatStringsSep;
+  localSystems = [
+    "builtin"
+    config.nixpkgs.hostPlatform.system
+  ] ++ config.nix.settings.extra-platforms;
+in
 {
   sops.secrets.hydra-admin-password.owner = "hydra";
   sops.secrets.hydra-users.owner = "hydra";
@@ -6,7 +18,7 @@
   # hydra-queue-runner needs to read this key for remote building
   sops.secrets.id_buildfarm.owner = "hydra-queue-runner";
 
-  nix.settings.keep-outputs = pkgs.lib.mkForce false;
+  nix.settings.keep-outputs = lib.mkForce false;
 
   nix.settings.allowed-uris = [
     "git+https:"
@@ -42,7 +54,7 @@
       '')
 
       (pkgs.writeText "local" ''
-        localhost x86_64-linux,builtin - 3 1 ${pkgs.lib.concatStringsSep "," config.nix.settings.system-features} - -
+        localhost ${concatStringsSep "," localSystems} - 3 1 ${concatStringsSep "," config.nix.settings.system-features} - -
       '')
     ];
     hydraURL = "https://hydra.nix-community.org";

modules/shared/nix-daemon.nix

@@ -9,6 +9,10 @@ let
   asGB = size: toString (size * 1024 * 1024 * 1024);
 in
 {
+  nixpkgs.hostPlatform = {
+    inherit (pkgs.hostPlatform) system;
+  };
+
   nix = {
     settings.trusted-public-keys = [
       "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="