Fix running NixOS tests on darwin (#405599)

Author: roberth

nixos/doc/manual/redirects.json

@@ -1874,6 +1874,9 @@
   "test-opt-meta.platforms": [
     "index.html#test-opt-meta.platforms"
   ],
+  "test-opt-meta.hydraPlatforms": [
+    "index.html#test-opt-meta.hydraPlatforms"
+  ],
   "test-opt-meta.timeout": [
     "index.html#test-opt-meta.timeout"
   ],

nixos/lib/testing/default.nix

@@ -9,15 +9,13 @@ let
     };
   runTest =
     module:
-    # Infra issue: virtualization on darwin doesn't seem to work yet.
-    lib.addMetaAttrs { hydraPlatforms = lib.platforms.linux; }
-      (evalTest (
-        { config, ... }:
-        {
-          imports = [ module ];
-          result = config.test;
-        }
-      )).config.result;
+    (evalTest (
+      { config, ... }:
+      {
+        imports = [ module ];
+        result = config.test;
+      }
+    )).config.result;
 
   testModules = [
     ./call-test.nix

nixos/lib/testing/meta.nix

@@ -1,50 +1,61 @@
 { lib, ... }:
 let
-  inherit (lib) types mkOption;
+  inherit (lib) types mkOption literalMD;
 in
 {
   options = {
-    meta = lib.mkOption {
+    meta = mkOption {
       description = ''
         The [`meta`](https://nixos.org/manual/nixpkgs/stable/#chap-meta) attributes that will be set on the returned derivations.
 
         Not all [`meta`](https://nixos.org/manual/nixpkgs/stable/#chap-meta) attributes are supported, but more can be added as desired.
       '';
       apply = lib.filterAttrs (k: v: v != null);
-      type = types.submodule {
-        options = {
-          maintainers = lib.mkOption {
-            type = types.listOf types.raw;
-            default = [ ];
-            description = ''
-              The [list of maintainers](https://nixos.org/manual/nixpkgs/stable/#var-meta-maintainers) for this test.
-            '';
+      type = types.submodule (
+        { config, ... }:
+        {
+          options = {
+            maintainers = mkOption {
+              type = types.listOf types.raw;
+              default = [ ];
+              description = ''
+                The [list of maintainers](https://nixos.org/manual/nixpkgs/stable/#var-meta-maintainers) for this test.
+              '';
+            };
+            timeout = mkOption {
+              type = types.nullOr types.int;
+              default = 3600; # 1 hour
+              description = ''
+                The [{option}`test`](#test-opt-test)'s [`meta.timeout`](https://nixos.org/manual/nixpkgs/stable/#var-meta-timeout) in seconds.
+              '';
+            };
+            broken = mkOption {
+              type = types.bool;
+              default = false;
+              description = ''
+                Sets the [`meta.broken`](https://nixos.org/manual/nixpkgs/stable/#var-meta-broken) attribute on the [{option}`test`](#test-opt-test) derivation.
+              '';
+            };
+            platforms = mkOption {
+              type = types.listOf types.raw;
+              default = lib.platforms.linux ++ lib.platforms.darwin;
+              description = ''
+                Sets the [`meta.platforms`](https://nixos.org/manual/nixpkgs/stable/#var-meta-platforms) attribute on the [{option}`test`](#test-opt-test) derivation.
+              '';
+            };
+            hydraPlatforms = mkOption {
+              type = types.listOf types.raw;
+              # Ideally this would default to `platforms` again:
+              # default = config.platforms;
+              default = lib.platforms.linux;
+              defaultText = literalMD "`lib.platforms.linux` only, as the `hydra.nixos.org` build farm does not currently support virtualisation on Darwin.";
+              description = ''
+                Sets the [`meta.hydraPlatforms`](https://nixos.org/manual/nixpkgs/stable/#var-meta-hydraPlatforms) attribute on the [{option}`test`](#test-opt-test) derivation.
+              '';
+            };
           };
-          timeout = lib.mkOption {
-            type = types.nullOr types.int;
-            default = 3600; # 1 hour
-            description = ''
-              The [{option}`test`](#test-opt-test)'s [`meta.timeout`](https://nixos.org/manual/nixpkgs/stable/#var-meta-timeout) in seconds.
-            '';
-          };
-          broken = lib.mkOption {
-            type = types.bool;
-            default = false;
-            description = ''
-              Sets the [`meta.broken`](https://nixos.org/manual/nixpkgs/stable/#var-meta-broken) attribute on the [{option}`test`](#test-opt-test) derivation.
-            '';
-          };
-          platforms = lib.mkOption {
-            type = types.listOf types.raw;
-            # darwin could be added, but it would add VM tests that don't work on Hydra.nixos.org (so far)
-            # see https://github.com/NixOS/nixpkgs/pull/303597#issuecomment-2128782362
-            default = lib.platforms.linux;
-            description = ''
-              Sets the [`meta.platforms`](https://nixos.org/manual/nixpkgs/stable/#var-meta-platforms) attribute on the [{option}`test`](#test-opt-test) derivation.
-            '';
-          };
-        };
-      };
+        }
+      );
       default = { };
     };
   };