From a742767bafecf0644585309b744e24f90cdff207 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 16 Jun 2023 21:28:06 +0200
Subject: nixos/nixpkgs: Make default Nixpkgs lazy when overridden

---
 nixos/modules/misc/nixpkgs.nix | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

(limited to 'nixos/modules/misc')

diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index 55ec08acf4453..8a20e31d5137b 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -337,7 +337,15 @@ 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 = [
-- 
cgit 1.4.1


From 8f31bff7940ed8d8d3e250e6ab7e7bc5b6160f1d Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 16 Jun 2023 21:45:09 +0200
Subject: nixos/nixpkgs: Don't check when _module.args.pkgs is set

---
 nixos/modules/misc/nixpkgs.nix | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

(limited to 'nixos/modules/misc')

diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index 8a20e31d5137b..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;
@@ -348,7 +343,17 @@ in
           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 =
-- 
cgit 1.4.1