From 3794246066409d7baac72e3fdfb0e4f66ef4a013 Mon Sep 17 00:00:00 2001
From: Jared Baur <jaredbaur@fastmail.com>
Date: Thu, 29 Feb 2024 19:22:33 -0800
Subject: [PATCH] nixos/nixpkgs: fix determination for cross-compiled nixos
 system

Since the output of `lib.systems.elaborate` contains functions, an
equality check with `==` does not suffice, `lib.systems.equals` should
be used instead.
---
 nixos/modules/misc/nixpkgs.nix      | 6 +++++-
 nixos/modules/misc/nixpkgs/test.nix | 6 ++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index da321a923449..10f800cd741a 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -208,7 +208,11 @@ in
       example = { system = "x86_64-linux"; };
       # Make sure that the final value has all fields for sake of other modules
       # referring to this.
-      apply = lib.systems.elaborate;
+      apply = inputBuildPlatform:
+        let elaborated = lib.systems.elaborate inputBuildPlatform;
+        in if lib.systems.equals elaborated cfg.hostPlatform
+          then cfg.hostPlatform  # make identical, so that `==` equality works; see https://github.com/NixOS/nixpkgs/issues/278001
+          else elaborated;
       defaultText = literalExpression
         ''config.nixpkgs.hostPlatform'';
       description = lib.mdDoc ''
diff --git a/nixos/modules/misc/nixpkgs/test.nix b/nixos/modules/misc/nixpkgs/test.nix
index 0536cfc9624a..be9a88a07788 100644
--- a/nixos/modules/misc/nixpkgs/test.nix
+++ b/nixos/modules/misc/nixpkgs/test.nix
@@ -12,6 +12,10 @@ let
     nixpkgs.hostPlatform = "aarch64-linux";
     nixpkgs.buildPlatform = "aarch64-darwin";
   };
+  withSameHostAndBuild = eval {
+    nixpkgs.hostPlatform = "aarch64-linux";
+    nixpkgs.buildPlatform = "aarch64-linux";
+  };
   ambiguous = {
     _file = "ambiguous.nix";
     nixpkgs.hostPlatform = "aarch64-linux";
@@ -81,6 +85,8 @@ lib.recurseIntoAttrs {
     assert withHost._module.args.pkgs.stdenv.buildPlatform.system == "aarch64-linux";
     assert withHostAndBuild._module.args.pkgs.stdenv.hostPlatform.system == "aarch64-linux";
     assert withHostAndBuild._module.args.pkgs.stdenv.buildPlatform.system == "aarch64-darwin";
+    assert withSameHostAndBuild.config.nixpkgs.buildPlatform == withSameHostAndBuild.config.nixpkgs.hostPlatform;
+    assert withSameHostAndBuild._module.args.pkgs.stdenv.buildPlatform == withSameHostAndBuild._module.args.pkgs.stdenv.hostPlatform;
     assert builtins.trace (lib.head (getErrors ambiguous))
       getErrors ambiguous ==
         [''