From 514529545bab291d6351935baeb409355c608207 Mon Sep 17 00:00:00 2001
From: DavHau <hsngrmpf+github@gmail.com>
Date: Thu, 19 Mar 2026 21:48:10 +0800
Subject: [PATCH] tests.top-level: add test for appendOverlays preserving
 splicing

Ensures that appendOverlays with an empty list returns spliced
packages, so that cross-compilation in NixOS modules works correctly.
---
 pkgs/test/top-level/default.nix | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/pkgs/test/top-level/default.nix b/pkgs/test/top-level/default.nix
index e713b617f8dd..3946b363b764 100644
--- a/pkgs/test/top-level/default.nix
+++ b/pkgs/test/top-level/default.nix
@@ -64,4 +64,22 @@ lib.recurseIntoAttrs {
     assert lib.all (p: p.stdenv.buildPlatform == p.stdenv.hostPlatform) pkgsLocal;
     assert lib.all (p: p.stdenv.buildPlatform != p.stdenv.hostPlatform) pkgsCross;
     pkgs.emptyFile;
+
+  # appendOverlays must preserve splicing so that cross-compilation
+  # works in NixOS modules (which go through appendOverlays via nixpkgs.nix).
+  appendOverlaysPreservesSplicing =
+    let
+      cross = nixpkgsFun {
+        localSystem = {
+          system = "x86_64-linux";
+        };
+        crossSystem = {
+          system = "aarch64-linux";
+        };
+      };
+      appended = cross.appendOverlays [ ];
+    in
+    assert cross.makeWrapper ? __spliced;
+    assert appended.makeWrapper ? __spliced;
+    pkgs.emptyFile;
 }