From 47de66b1a437c8dbef29b03be51dedb2274d0006 Mon Sep 17 00:00:00 2001
From: Adam Joseph <adam@westernsemico.com>
Date: Mon, 5 Sep 2022 16:11:50 -0700
Subject: [PATCH] lib/attrsets.nix: add unionOfDisjoint

---
 lib/attrsets.nix | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/attrsets.nix b/lib/attrsets.nix
index 5575e9577029..6c666ea375e5 100644
--- a/lib/attrsets.nix
+++ b/lib/attrsets.nix
@@ -622,6 +622,16 @@ rec {
   dontRecurseIntoAttrs =
     attrs: attrs // { recurseForDerivations = false; };
 
+  /* `unionOfDisjoint x y` is equal to `x // y // z` where the
+     attrnames in `z` are the intersection of the attrnames in `x` and
+     `y`, and all values `assert` with an error message */
+  unionOfDisjoint = x: y:
+    x // (mapAttrs
+      (name: val:
+        if hasAttr name x
+        then builtins.throw "attribute collision: ${name}"
+        else val) y);
+
   /*** deprecated stuff ***/
 
   zipWithNames = zipAttrsWithNames;