From c53673e0ad73fecf79be4df61be01e91c0a7f230 Mon Sep 17 00:00:00 2001
From: dramforever <dramforever@live.com>
Date: Tue, 7 Apr 2026 15:53:57 +0800
Subject: [PATCH 1/2] fetchClosure: Add temproot before checking path

This avoids the fetched path from getting garbage collected if it is
already valid.
---
 src/libexpr/primops/fetchClosure.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/libexpr/primops/fetchClosure.cc b/src/libexpr/primops/fetchClosure.cc
index 0f7eafefe9e6..84bce6116ea3 100644
--- a/src/libexpr/primops/fetchClosure.cc
+++ b/src/libexpr/primops/fetchClosure.cc
@@ -24,6 +24,8 @@ static void runFetchClosureWithRewrite(
     const std::optional<StorePath> & toPathMaybe,
     Value & v)
 {
+    if (toPathMaybe)
+        state.store->addTempRoot(*toPathMaybe);
 
     // establish toPath or throw
 
@@ -75,6 +77,7 @@ static void runFetchClosureWithRewrite(
 static void runFetchClosureWithContentAddressedPath(
     EvalState & state, const PosIdx pos, Store & fromStore, const StorePath & fromPath, Value & v)
 {
+    state.store->addTempRoot(fromPath);
 
     if (!state.store->isValidPath(fromPath))
         copyClosure(fromStore, *state.store, RealisedPath::Set{fromPath});
@@ -104,6 +107,7 @@ static void runFetchClosureWithContentAddressedPath(
 static void runFetchClosureWithInputAddressedPath(
     EvalState & state, const PosIdx pos, Store & fromStore, const StorePath & fromPath, Value & v)
 {
+    state.store->addTempRoot(fromPath);
 
     if (!state.store->isValidPath(fromPath))
         copyClosure(fromStore, *state.store, RealisedPath::Set{fromPath});

From 734a205d58a559a622ebc98256f4af4d968426b7 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 3 Jun 2026 16:27:16 +0200
Subject: [PATCH 2/2] copyPaths(): Register temp roots on the destination store

Note: this only prevents the paths from being GCed during the
copy. You still need to use `nix copy --out-link ...` to prevent GC
afterwards.

Less ambitious fix than https://github.com/NixOS/nix/pull/15719.
---
 src/libstore/store-api.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 1145c2574e56..edc8daafc137 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1040,6 +1040,9 @@ std::map<StorePath, StorePath> copyPaths(
     CheckSigsFlag checkSigs,
     SubstituteFlag substitute)
 {
+    for (auto & path : storePaths)
+        dstStore.addTempRoot(path);
+
     auto valid = dstStore.queryValidPaths(storePaths, substitute);
 
     StorePathSet missing;