Merge branch 'jk/midx-write-v1-by-default'

As writing version 2 MIDX files by default breaks older versions of
Git and its reimplementations, use V2 only when necessary.

* jk/midx-write-v1-by-default:
  MIDX: revert the default version to v1

Documentation/git-multi-pack-index.adoc

@@ -98,6 +98,9 @@ compact::
 	--[no-]bitmap::
 		Control whether or not a multi-pack bitmap is written.
 --
++
+Note that the compact command requires writing a version-2 midx that
+cannot be read by versions of Git prior to v2.54.
 
 verify::
 	Verify the contents of the MIDX file.

midx-write.c

@@ -1259,7 +1259,6 @@ 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,
 	 };
 	struct multi_pack_index *midx_to_free = NULL;
 	int bitmapped_packs_concat_len = 0;
@@ -1275,6 +1274,9 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	ctx.repo = r;
 	ctx.source = opts->source;
 
+	ctx.version = ((opts->flags & MIDX_WRITE_COMPACT)
+		       ? MIDX_VERSION_V2
+		       : MIDX_VERSION_V1);
 	repo_config_get_int(ctx.repo, "midx.version", &ctx.version);
 	if (ctx.version != MIDX_VERSION_V1 && ctx.version != MIDX_VERSION_V2)
 		die(_("unknown MIDX version: %d"), ctx.version);

t/t5319-multi-pack-index.sh

@@ -21,7 +21,7 @@ midx_read_expect () {
 	EXTRA_CHUNKS="$5"
 	{
 		cat <<-EOF &&
-		header: 4d494458 2 $HASH_LEN $NUM_CHUNKS $NUM_PACKS
+		header: 4d494458 1 $HASH_LEN $NUM_CHUNKS $NUM_PACKS
 		chunks: pack-names oid-fanout oid-lookup object-offsets$EXTRA_CHUNKS
 		num_objects: $NUM_OBJECTS
 		packs: