Merge pull request #238136 from hercules-ci/nixos-nixpkgs-dont-check-when-_module.args.pkgs-is-set

`nixos/nixpkgs`: Don't check when `_module.args.pkgs` is set

1 files changed, 20 insertions, 7 deletions

diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index 55ec08acf4453..f9d8bccea2843 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -55,11 +55,6 @@ let
     description = "An evaluation of Nixpkgs; the top level attribute set of packages";
   };
 
-  # Whether `pkgs` was constructed by this module - not if nixpkgs.pkgs or
-  # _module.args.pkgs is set. However, determining whether _module.args.pkgs
-  # is defined elsewhere does not seem feasible.
-  constructedByMe = !opt.pkgs.isDefined;
-
   hasBuildPlatform = opt.buildPlatform.highestPrio < (mkOptionDefault {}).priority;
   hasHostPlatform = opt.hostPlatform.isDefined;
   hasPlatform = hasHostPlatform || hasBuildPlatform;
@@ -337,10 +332,28 @@ in
 
   config = {
     _module.args = {
-      pkgs = finalPkgs.__splicedPackages;
+      pkgs =
+        # We explicitly set the default override priority, so that we do not need
+        # to evaluate finalPkgs in case an override is placed on `_module.args.pkgs`.
+        # After all, to determine a definition priority, we need to evaluate `._type`,
+        # which is somewhat costly for Nixpkgs. With an explicit priority, we only
+        # evaluate the wrapper to find out that the priority is lower, and then we
+        # don't need to evaluate `finalPkgs`.
+        lib.mkOverride lib.modules.defaultOverridePriority
+          finalPkgs.__splicedPackages;
     };
 
-    assertions = [
+    assertions = let
+      # Whether `pkgs` was constructed by this module. This is false when any of
+      # nixpkgs.pkgs or _module.args.pkgs is set.
+      constructedByMe =
+        # We set it with default priority and it can not be merged, so if the
+        # pkgs module argument has that priority, it's from us.
+        (lib.modules.mergeAttrDefinitionsWithPrio options._module.args).pkgs.highestPrio
+          == lib.modules.defaultOverridePriority
+        # Although, if nixpkgs.pkgs is set, we did forward it, but we did not construct it.
+          && !opt.pkgs.isDefined;
+    in [
       (
         let
           nixosExpectedSystem =