From 8cbf862e6f6e8250d59491fdb88dfc11a805a970 Mon Sep 17 00:00:00 2001
From: Alexander Bantyev <balsoft@balsoft.ru>
Date: Thu, 2 Dec 2021 11:35:50 +0300
Subject: [PATCH] Flakes: computeLocks: pass correct LockParent when reusing
 oldLock

Previously, when we were attempting to reuse the old lockfile
information in the computeLocks function, we have passed the parent of
the current input to the next computeLocks call. This was incorrect,
since the follows are resolved relative to the parent. This caused
issues when we tried to reuse oldLock but couldn't for some
reason (read: mustRefetch is true), in that case the follows were
resolved incorrectly.

Fix this by passing the correct parent, and adding some tests to
prevent this particular regression from happening again.

Closes https://github.com/NixOS/nix/issues/5697
---
 src/libexpr/flake/flake.cc |  7 ++++++-
 tests/flakes.sh            | 12 ++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 06136579e..33d253eee 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -480,11 +480,16 @@ LockedFlake lockFlake(
                             }
                         }
 
+                        LockParent newParent {
+                            .path = inputPath,
+                            .absolute = false
+                        };
+
                         computeLocks(
                             mustRefetch
                             ? getFlake(state, oldLock->lockedRef, false, flakeCache).inputs
                             : fakeInputs,
-                            childNode, inputPath, oldLock, parent, parentPath);
+                            childNode, inputPath, oldLock, newParent, parentPath);
 
                     } else {
                         /* We need to create a new lock file entry. So fetch
diff --git a/tests/flakes.sh b/tests/flakes.sh
index 9e10322b9..20966ab2a 100644
--- a/tests/flakes.sh
+++ b/tests/flakes.sh
@@ -722,6 +722,7 @@ cat > $flakeFollowsB/flake.nix <<EOF
     inputs = {
         foobar.url = "path:$flakeFollowsA/flakeE";
         nonFlake.url = "path:$nonFlakeDir";
+        goodoo.follows = "C/goodoo";
         C = {
             url = "path:./flakeC";
             inputs.foobar.follows = "foobar";
@@ -736,6 +737,7 @@ cat > $flakeFollowsC/flake.nix <<EOF
     description = "Flake C";
     inputs = {
         foobar.url = "path:$flakeFollowsA/flakeE";
+        goodoo.follows = "foobar";
     };
     outputs = { ... }: {};
 }
@@ -760,8 +762,18 @@ EOF
 git -C $flakeFollowsA add flake.nix flakeB/flake.nix \
   flakeB/flakeC/flake.nix flakeD/flake.nix flakeE/flake.nix
 
+nix flake update $flakeFollowsA
+
+oldLock="$(cat "$flakeFollowsA/flake.lock")"
+
+# Ensure that locking twice doesn't change anything
+
 nix flake lock $flakeFollowsA
 
+newLock="$(cat "$flakeFollowsA/flake.lock")"
+
+diff <(echo "$newLock") <(echo "$oldLock")
+
 [[ $(jq -c .nodes.B.inputs.C $flakeFollowsA/flake.lock) = '"C"' ]]
 [[ $(jq -c .nodes.B.inputs.foobar $flakeFollowsA/flake.lock) = '["D"]' ]]
 [[ $(jq -c .nodes.C.inputs.foobar $flakeFollowsA/flake.lock) = '["B","foobar"]' ]]