From bc4b353bff355ac5ef69609a525285a93029db04 Mon Sep 17 00:00:00 2001
From: Eman Resu <78693624+quatquatt@users.noreply.github.com>
Date: Thu, 14 May 2026 12:52:04 -0400
Subject: [PATCH] lib.attrsets.matchAttrs: only assert isAttrs once

---
 lib/attrsets.nix | 35 ++++++++++++++++++++---------------
 1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/lib/attrsets.nix b/lib/attrsets.nix
index 7dae595c9e39..96af967c53f8 100644
--- a/lib/attrsets.nix
+++ b/lib/attrsets.nix
@@ -1800,22 +1800,27 @@ rec {
     :::
   */
   matchAttrs =
-    pattern: attrs:
+    let
+      recurse =
+        pattern: attrs:
+        all (
+          # Compare equality between `pattern` & `attrs`.
+          attr:
+          # Missing attr, not equal.
+          attrs ? ${attr}
+          && (
+            let
+              lhs = pattern.${attr};
+              rhs = attrs.${attr};
+            in
+            # If attrset check recursively
+            if isAttrs lhs then isAttrs rhs && recurse lhs rhs else lhs == rhs
+          )
+        ) (attrNames pattern);
+    in
+    pattern:
     assert isAttrs pattern;
-    all (
-      # Compare equality between `pattern` & `attrs`.
-      attr:
-      # Missing attr, not equal.
-      attrs ? ${attr}
-      && (
-        let
-          lhs = pattern.${attr};
-          rhs = attrs.${attr};
-        in
-        # If attrset check recursively
-        if isAttrs lhs then isAttrs rhs && matchAttrs lhs rhs else lhs == rhs
-      )
-    ) (attrNames pattern);
+    recurse pattern;
 
   /**
     Override only the attributes that are already present in the old set