mktree: do not use OBJECT_INFO_QUICK when checking objects

mktree_line() checks each referenced object's type with
odb_read_object_info_extended() under OBJECT_INFO_QUICK.  QUICK skips the
reprepare-and-retry that reloads the on-disk pack set, so a resident
"git mktree --batch" reader reports an object that a concurrent repack
just relocated into a new pack as missing, and rejects the entry.

QUICK entered this lookup in 817b0f602710 (mktree: do not check type of
remote objects, 2022-06-21) only to avoid lazily fetching promisor
objects; OBJECT_INFO_SKIP_FETCH_OBJECT already provides that.  Drop
OBJECT_INFO_QUICK and keep OBJECT_INFO_SKIP_FETCH_OBJECT, so mktree still
avoids a promisor fetch but recovers an object that was merely repacked.

Add a regression test driving a resident mktree --batch reader across a
concurrent repack that retires a pack.

Assisted-by: Claude Opus 4.8 & GPT-5.6 Sol
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 48 insertions, 1 deletions

diff --git a/builtin/mktree.c b/builtin/mktree.c
index dc2d293c3d..45ae2af3b5 100644
--- a/builtin/mktree.c
+++ b/builtin/mktree.c
@@ -125,7 +125,6 @@ static void mktree_line(struct repository *repo, char *buf, int nul_term_line, i
 	oi.typep = &obj_type;
 	if (odb_read_object_info_extended(repo->objects, &oid, &oi,
 					  OBJECT_INFO_LOOKUP_REPLACE |
-					  OBJECT_INFO_QUICK |
 					  OBJECT_INFO_SKIP_FETCH_OBJECT) < 0)
 		obj_type = -1;
 
diff --git a/t/t1010-mktree.sh b/t/t1010-mktree.sh
index 312fe6717a..cecba55d45 100755
--- a/t/t1010-mktree.sh
+++ b/t/t1010-mktree.sh
@@ -69,4 +69,52 @@ test_expect_success 'mktree refuses to read ls-tree -r output (2)' '
 	test_must_fail git mktree <all.withsub
 '
 
+test_expect_success PIPE 'mktree --batch survives a concurrent repack retiring a pack' '
+	test_when_finished "rm -fr race" &&
+	git init race &&
+	(
+		cd race &&
+		test_commit seed &&
+		a=$(echo A | git hash-object -w --stdin) &&
+		b=$(echo B | git hash-object -w --stdin) &&
+		echo "$a" | git pack-objects .git/objects/pack/pack >pack-a &&
+		echo "$b" | git pack-objects .git/objects/pack/pack >pack-b &&
+
+		# Drop the loose copies so the blobs resolve only through the
+		# packs the multi-pack-index names.
+		git prune-packed &&
+		git multi-pack-index write &&
+		printf "100644 blob %s\ta\n" "$a" >tree-a &&
+		printf "100644 blob %s\tb\n" "$b" >tree-b &&
+
+		victim=".git/objects/pack/pack-$(cat pack-b)" &&
+		mkfifo in out &&
+
+		# mktree --batch stays resident, so its pack view predates the
+		# repack below; feed it one tree at a time over a fifo.  The
+		# subshell exit closes the fifos, letting mktree see EOF and quit.
+		(git mktree --batch <in >out 2>err &) &&
+		exec 9>in &&
+		exec 8<out &&
+
+		# The first tree makes the reader cache its (soon stale) view.
+		cat tree-a >&9 && echo >&9 && read tree_a <&8 &&
+
+		# Mimic a concurrent repack: a replacement pack holds every
+		# object, and the pack for b loses its .idx (its .pack lingers),
+		# matching the order in which unlink_pack_path() removes files.
+		git cat-file --batch-all-objects --batch-check="%(objectname)" >oids &&
+		git pack-objects .git/objects/pack/pack <oids >/dev/null &&
+		rm -f "$victim.idx" &&
+
+		# Resolving b used to fail, as its QUICK lookup accepted the
+		# miss; without QUICK the reader repreps and finds b in the
+		# replacement pack.
+		cat tree-b >&9 && echo >&9 && read tree_b <&8 &&
+		exec 9>&- &&
+
+		test -n "$tree_b"
+	)
+'
+
 test_done