From 185153fbb695b60f95972f2823d6c17d28f74fee Mon Sep 17 00:00:00 2001
From: Adam Joseph <adam@westernsemico.com>
Date: Mon, 23 Oct 2023 23:58:29 -0700
Subject: [PATCH] top-level/splice.nix: add NIXPKGS_ALWAYS_SPLICE debugging aid

---
 pkgs/top-level/splice.nix | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/pkgs/top-level/splice.nix b/pkgs/top-level/splice.nix
index 9ac0fe2200f92..6780600c10b40 100644
--- a/pkgs/top-level/splice.nix
+++ b/pkgs/top-level/splice.nix
@@ -14,6 +14,15 @@
 # For performance reasons, rather than uniformally splice in all cases, we only
 # do so when `pkgs` and `buildPackages` are distinct. The `actuallySplice`
 # parameter there the boolean value of that equality check.
+
+let
+  # This is for debugging only.  It significantly degrades
+  # performance.  In theory it is impure, but in practice it should
+  # not affect the result of eval unless you're going out of your
+  # way to detect that it has been set (i.e. myDrv?__spliced).
+  NIXPKGS_ALWAYS_SPLICE = builtins.getEnv("NIXPKGS_ALWAYS_SPLICE") != "";
+in
+
 lib: pkgs: actuallySplice:
 
 let
@@ -102,7 +111,9 @@ let
     , pkgsHostTarget
     , pkgsTargetTarget
     } @ args:
-    if actuallySplice then spliceReal args else pkgsHostTarget;
+    if !NIXPKGS_ALWAYS_SPLICE && actuallySplice
+    then pkgsHostTarget
+    else spliceReal args;
 
   splicedPackages = splicePackages
     {