From 247cc7013a0bd48fa237842da7c3592b77137767 Mon Sep 17 00:00:00 2001
From: Sergei Zimmerman <sergei@zimmerman.foo>
Date: Thu, 19 Feb 2026 02:46:53 +0300
Subject: [PATCH] libexpr: Use temporary value in ExprOpUpdate::eval

---
 src/libexpr/eval.cc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index b8ed0a6aa..ba52e813b 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1987,11 +1987,15 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
     UpdateQueue q;
     evalForUpdate(state, env, q);
 
-    v.mkAttrs(&Bindings::emptyBindings);
+    Value vTmp;
+    vTmp.mkAttrs(&Bindings::emptyBindings);
+
     for (auto & rhs : std::views::reverse(q)) {
         /* Remember that queue is sorted rightmost attrset first. */
-        eval(state, /*v=*/v, /*v1=*/v, /*v2=*/rhs);
+        eval(state, /*v=*/vTmp, /*v1=*/vTmp, /*v2=*/rhs);
     }
+
+    v = vTmp;
 }
 
 void Expr::evalForUpdate(EvalState & state, Env & env, UpdateQueue & q, std::string_view errorCtx)