Subject: Re: MIDX woes, was Re: [ANNOUNCE] Git v2.54.0-rc2

From: Junio C Hamano <[email-masked]>
Date: Thu, 16 Apr 2026 11:10:15 -0700

Jeff King <[email-masked]> writes:

> On Thu, Apr 16, 2026 at 01:17:33AM -0400, Jeff King wrote:
>
>> I think removing the .midx file (and optionally regenerating with the
>> old version) would be the appropriate workaround, but I wonder how hard
>> it would be to go back to generating v1 midx files by default. I know v2
>> is a building block for more advanced features, but for those who are
>> not using those features yet it is a strict regression.
>
> I think doing so is just this one-liner:

Let's do this before Git 2.54 final, then.

----- >8 -----
From: Jeff King <[email-masked]>
Date: Thu, 16 Apr 2026 10:56:20 -0700
Subject: [PATCH] MIDX: keep the default version to MIDX v1

As deployed versions of Git and its reimplementations may not be
ready for the format bump, let's revert the default version of MIDX
file we write back to V1, and adjust the tests so that the ones that
do test features that require V2 to explicitly ask for it.

Signed-off-by: Junio C Hamano <[email-masked]>
---
 midx-write.c                        | 2 +-
 t/t5319-multi-pack-index.sh         | 5 ++++-
 t/t5335-compact-multi-pack-index.sh | 7 +++++++
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/midx-write.c b/midx-write.c
index 0ff2e45aa7..607de889f9 100644
--- a/midx-write.c
+++ b/midx-write.c
@@ -1259,7 +1259,7 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	struct tempfile *incr;
 	struct write_midx_context ctx = {
 		.preferred_pack_idx = NO_PREFERRED_PACK,
-		.version = MIDX_VERSION_V2,
+		.version = MIDX_VERSION_V1,
 	 };
 	struct multi_pack_index *midx_to_free = NULL;
 	int bitmapped_packs_concat_len = 0;
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 58e0b685b1..ed1f993a74 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -19,9 +19,12 @@ midx_read_expect () {
 	NUM_CHUNKS=$3
 	OBJECT_DIR=$4
 	EXTRA_CHUNKS="$5"
+	# This reflects the default midx version we write; it should switch
+	# to 2 if we flip the default.
+	VERSION=1
 	{
 		cat <<-EOF &&
-		header: 4d494458 2 $HASH_LEN $NUM_CHUNKS $NUM_PACKS
+		header: 4d494458 $VERSION $HASH_LEN $NUM_CHUNKS $NUM_PACKS
 		chunks: pack-names oid-fanout oid-lookup object-offsets$EXTRA_CHUNKS
 		num_objects: $NUM_OBJECTS
 		packs:
diff --git a/t/t5335-compact-multi-pack-index.sh b/t/t5335-compact-multi-pack-index.sh
index 40f3844282..4ad007169a 100755
--- a/t/t5335-compact-multi-pack-index.sh
+++ b/t/t5335-compact-multi-pack-index.sh
@@ -57,6 +57,13 @@ test_midx_layer_object_uniqueness () {
 	done <$midx_chain
 }
 
+# MIDX compaction requires the v2 format, so make it the default
+# for the rest of this script. We check below that trying
+# compaction with v1 fails using "git -c", which will override this.
+test_expect_success 'set midx version config' '
+	git config --global midx.version 2
+'
+
 test_expect_success 'MIDX compaction with lex-ordered pack names' '
 	git init midx-compact-lex-order &&
 	(
-- 
2.54.0-rc2-109-g879cd67f0d