From 2ecc5156f47767fcf06504b97c38ad494dc3f924 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 9 Jul 2025 17:00:49 +0200
Subject: [PATCH] lockFlake(): When updating a lock, respect the input's lock
 file

---
 src/libflake/flake.cc             | 10 +++-----
 tests/functional/flakes/flakes.sh | 38 +++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/src/libflake/flake.cc b/src/libflake/flake.cc
index 075708234..34d094d52 100644
--- a/src/libflake/flake.cc
+++ b/src/libflake/flake.cc
@@ -723,16 +723,12 @@ LockedFlake lockFlake(
                             Finally cleanup([&]() { parents.pop_back(); });
 
                             /* Recursively process the inputs of this
-                               flake. Also, unless we already have this flake
-                               in the top-level lock file, use this flake's
-                               own lock file. */
+                               flake, using its own lock file. */
                             nodePaths.emplace(childNode, inputFlake.path.parent());
                             computeLocks(
                                 inputFlake.inputs, childNode, inputAttrPath,
-                                oldLock
-                                ? std::dynamic_pointer_cast<const Node>(oldLock)
-                                : readLockFile(state.fetchSettings, inputFlake.lockFilePath()).root.get_ptr(),
-                                oldLock ? followsPrefix : inputAttrPath,
+                                readLockFile(state.fetchSettings, inputFlake.lockFilePath()).root.get_ptr(),
+                                inputAttrPath,
                                 inputFlake.path,
                                 false);
 
diff --git a/tests/functional/flakes/flakes.sh b/tests/functional/flakes/flakes.sh
index cfd204569..35b6558ff 100755
--- a/tests/functional/flakes/flakes.sh
+++ b/tests/functional/flakes/flakes.sh
@@ -446,3 +446,41 @@ nix flake metadata "$flake2Dir" --reference-lock-file $TEST_ROOT/flake2-overridd
 
 # reference-lock-file can only be used if allow-dirty is set.
 expectStderr 1 nix flake metadata "$flake2Dir" --no-allow-dirty --reference-lock-file $TEST_ROOT/flake2-overridden.lock
+
+# After changing an input (flake2 from newFlake2Rev to prevFlake2Rev), we should have the transitive inputs locked by revision $prevFlake2Rev of flake2.
+prevFlake1Rev=$(nix flake metadata --json "$flake1Dir" | jq -r .revision)
+prevFlake2Rev=$(nix flake metadata --json "$flake2Dir" | jq -r .revision)
+
+echo "# bla" >> "$flake1Dir/flake.nix"
+git -C "$flake1Dir" commit flake.nix -m 'bla'
+
+nix flake update --flake "$flake2Dir"
+git -C "$flake2Dir" commit flake.lock -m 'bla'
+
+newFlake1Rev=$(nix flake metadata --json "$flake1Dir" | jq -r .revision)
+newFlake2Rev=$(nix flake metadata --json "$flake2Dir" | jq -r .revision)
+
+cat > "$flake3Dir/flake.nix" <<EOF
+{
+  inputs.flake2.url = "flake:flake2/master/$newFlake2Rev";
+
+  outputs = { self, flake2 }: {
+  };
+}
+EOF
+git -C "$flake3Dir" commit flake.nix -m 'bla'
+
+rm "$flake3Dir/flake.lock"
+nix flake lock "$flake3Dir"
+[[ "$(nix flake metadata --json "$flake3Dir" | jq -r .locks.nodes.flake1.locked.rev)" = $newFlake1Rev ]]
+
+cat > "$flake3Dir/flake.nix" <<EOF
+{
+  inputs.flake2.url = "flake:flake2/master/$prevFlake2Rev";
+
+  outputs = { self, flake2 }: {
+  };
+}
+EOF
+
+[[ "$(nix flake metadata --json "$flake3Dir" | jq -r .locks.nodes.flake1.locked.rev)" = $prevFlake1Rev ]]