diff --git a/Documentation/git-multi-pack-index.adoc b/Documentation/git-multi-pack-index.adoc
index 164cf1f229..883a052974 100644
--- a/Documentation/git-multi-pack-index.adoc
+++ b/Documentation/git-multi-pack-index.adoc
@@ -12,6 +12,8 @@ SYNOPSIS
 'git multi-pack-index' [<options>] write [--preferred-pack=<pack>]
 		         [--[no-]bitmap] [--[no-]incremental] [--[no-]stdin-packs]
 		         [--refs-snapshot=<path>]
+'git multi-pack-index' [<options>] compact [--[no-]incremental]
+		         <from> <to>
 'git multi-pack-index' [<options>] verify
 'git multi-pack-index' [<options>] expire
 'git multi-pack-index' [<options>] repack [--batch-size=<size>]
@@ -83,6 +85,17 @@ marker).
 		necessary.
 --
 
+compact::
+	Write a new MIDX layer containing only objects and packs present
+	in the range `<from>` to `<to>`, where both arguments are
+	checksums of existing layers in the MIDX chain.
++
+--
+	--incremental::
+		Write the result to a MIDX chain instead of writing a
+		stand-alone MIDX.
+--
+
 verify::
 	Verify the contents of the MIDX file.
 
diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index c0c6c1760c..043ee8c478 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -17,6 +17,10 @@
 	   "  [--[no-]bitmap] [--[no-]incremental] [--[no-]stdin-packs]\n" \
 	   "  [--refs-snapshot=<path>]")
 
+#define BUILTIN_MIDX_COMPACT_USAGE \
+	N_("git multi-pack-index [<options>] compact [--[no-]incremental]\n" \
+	   "  <from> <to>")
+
 #define BUILTIN_MIDX_VERIFY_USAGE \
 	N_("git multi-pack-index [<options>] verify")
 
@@ -30,6 +34,10 @@ static char const * const builtin_multi_pack_index_write_usage[] = {
 	BUILTIN_MIDX_WRITE_USAGE,
 	NULL
 };
+static char const * const builtin_multi_pack_index_compact_usage[] = {
+	BUILTIN_MIDX_COMPACT_USAGE,
+	NULL
+};
 static char const * const builtin_multi_pack_index_verify_usage[] = {
 	BUILTIN_MIDX_VERIFY_USAGE,
 	NULL
@@ -44,6 +52,7 @@ static char const * const builtin_multi_pack_index_repack_usage[] = {
 };
 static char const * const builtin_multi_pack_index_usage[] = {
 	BUILTIN_MIDX_WRITE_USAGE,
+	BUILTIN_MIDX_COMPACT_USAGE,
 	BUILTIN_MIDX_VERIFY_USAGE,
 	BUILTIN_MIDX_EXPIRE_USAGE,
 	BUILTIN_MIDX_REPACK_USAGE,
@@ -195,6 +204,70 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 	return ret;
 }
 
+static int cmd_multi_pack_index_compact(int argc, const char **argv,
+					const char *prefix,
+					struct repository *repo)
+{
+	struct multi_pack_index *m, *cur;
+	struct multi_pack_index *from_midx = NULL;
+	struct multi_pack_index *to_midx = NULL;
+	struct odb_source *source;
+	int ret;
+
+	struct option *options;
+	static struct option builtin_multi_pack_index_compact_options[] = {
+		OPT_BIT(0, "incremental", &opts.flags,
+			N_("write a new incremental MIDX"), MIDX_WRITE_INCREMENTAL),
+		OPT_END(),
+	};
+
+	repo_config(repo, git_multi_pack_index_write_config, NULL);
+
+	options = add_common_options(builtin_multi_pack_index_compact_options);
+
+	trace2_cmd_mode(argv[0]);
+
+	if (isatty(2))
+		opts.flags |= MIDX_PROGRESS;
+	argc = parse_options(argc, argv, prefix,
+			     options, builtin_multi_pack_index_compact_usage,
+			     0);
+
+	if (argc != 2)
+		usage_with_options(builtin_multi_pack_index_compact_usage,
+				   options);
+	source = handle_object_dir_option(the_repository);
+
+	FREE_AND_NULL(options);
+
+	m = get_multi_pack_index(source);
+
+	for (cur = m; cur && !(from_midx && to_midx); cur = cur->base_midx) {
+		const char *midx_csum = midx_get_checksum_hex(cur);
+
+		if (!from_midx && !strcmp(midx_csum, argv[0]))
+			from_midx = cur;
+		if (!to_midx && !strcmp(midx_csum, argv[1]))
+			to_midx = cur;
+	}
+
+	if (!from_midx)
+		die(_("could not find MIDX: %s"), argv[0]);
+	if (!to_midx)
+		die(_("could not find MIDX: %s"), argv[1]);
+	if (from_midx == to_midx)
+		die(_("MIDX compaction endpoints must be unique"));
+
+	for (m = from_midx; m; m = m->base_midx) {
+		if (m == to_midx)
+			die(_("MIDX %s must be an ancestor of %s"), argv[0], argv[1]);
+	}
+
+	ret = write_midx_file_compact(source, from_midx, to_midx, opts.flags);
+
+	return ret;
+}
+
 static int cmd_multi_pack_index_verify(int argc, const char **argv,
 				       const char *prefix,
 				       struct repository *repo UNUSED)
@@ -295,6 +368,7 @@ int cmd_multi_pack_index(int argc,
 	struct option builtin_multi_pack_index_options[] = {
 		OPT_SUBCOMMAND("repack", &fn, cmd_multi_pack_index_repack),
 		OPT_SUBCOMMAND("write", &fn, cmd_multi_pack_index_write),
+		OPT_SUBCOMMAND("compact", &fn, cmd_multi_pack_index_compact),
 		OPT_SUBCOMMAND("verify", &fn, cmd_multi_pack_index_verify),
 		OPT_SUBCOMMAND("expire", &fn, cmd_multi_pack_index_expire),
 		OPT_END(),
diff --git a/midx-write.c b/midx-write.c
index ca2469213e..afa077a09c 100644
--- a/midx-write.c
+++ b/midx-write.c
@@ -113,6 +113,10 @@ struct write_midx_context {
 	int incremental;
 	uint32_t num_multi_pack_indexes_before;
 
+	struct multi_pack_index *compact_from;
+	struct multi_pack_index *compact_to;
+	int compact;
+
 	struct string_list *to_include;
 
 	struct repository *repo;
@@ -122,6 +126,8 @@ struct write_midx_context {
 static uint32_t midx_pack_perm(struct write_midx_context *ctx,
 			       uint32_t orig_pack_int_id)
 {
+	if (ctx->compact)
+		orig_pack_int_id -= ctx->compact_from->num_packs_in_base;
 	return ctx->pack_perm[orig_pack_int_id];
 }
 
@@ -352,6 +358,21 @@ static void midx_fanout_add(struct midx_fanout *fanout,
 					    cur_fanout);
 }
 
+static void midx_fanout_add_compact(struct midx_fanout *fanout,
+				    struct write_midx_context *ctx,
+				    uint32_t cur_fanout)
+{
+	struct multi_pack_index *m = ctx->compact_to;
+
+	ASSERT(ctx->compact);
+
+	while (m && m != ctx->compact_from->base_midx) {
+		midx_fanout_add_midx_fanout(fanout, m, cur_fanout,
+					    NO_PREFERRED_PACK);
+		m = m->base_midx;
+	}
+}
+
 /*
  * It is possible to artificially get into a state where there are many
  * duplicate copies of objects. That can create high memory pressure if
@@ -370,6 +391,9 @@ static void compute_sorted_entries(struct write_midx_context *ctx,
 	size_t alloc_objects, total_objects = 0;
 	struct midx_fanout fanout = { 0 };
 
+	if (ctx->compact)
+		ASSERT(!start_pack);
+
 	for (cur_pack = start_pack; cur_pack < ctx->nr; cur_pack++)
 		total_objects = st_add(total_objects,
 				       ctx->info[cur_pack].p->num_objects);
@@ -388,7 +412,10 @@ static void compute_sorted_entries(struct write_midx_context *ctx,
 	for (cur_fanout = 0; cur_fanout < 256; cur_fanout++) {
 		fanout.nr = 0;
 
-		midx_fanout_add(&fanout, ctx, start_pack, cur_fanout);
+		if (ctx->compact)
+			midx_fanout_add_compact(&fanout, ctx, cur_fanout);
+		else
+			midx_fanout_add(&fanout, ctx, start_pack, cur_fanout);
 		midx_fanout_sort(&fanout);
 
 		/*
@@ -956,6 +983,72 @@ static int fill_packs_from_midx(struct write_midx_context *ctx)
 	return 0;
 }
 
+static uint32_t compactible_packs_between(const struct multi_pack_index *from,
+					  const struct multi_pack_index *to)
+{
+	uint32_t nr;
+
+	ASSERT(from && to);
+
+	nr = u32_add(to->num_packs, to->num_packs_in_base);
+	if (nr < from->num_packs_in_base)
+		BUG("unexpected number of packs in base during compaction: "
+		    "%"PRIu32" < %"PRIu32, nr, from->num_packs_in_base);
+
+	return nr - from->num_packs_in_base;
+}
+
+static int fill_packs_from_midx_range(struct write_midx_context *ctx,
+				      int bitmap_order)
+{
+	struct multi_pack_index *m = ctx->compact_to;
+	uint32_t packs_nr;
+
+	ASSERT(ctx->compact && !ctx->nr);
+	ASSERT(ctx->compact_from);
+	ASSERT(ctx->compact_to);
+
+	packs_nr = compactible_packs_between(ctx->compact_from,
+					     ctx->compact_to);
+
+	ALLOC_GROW(ctx->info, packs_nr, ctx->alloc);
+
+	while (m != ctx->compact_from->base_midx) {
+		uint32_t pack_int_id, preferred_pack_id;
+		uint32_t i;
+
+		if (bitmap_order) {
+			if (midx_preferred_pack(m, &preferred_pack_id) < 0)
+				die(_("could not determine preferred pack"));
+		} else {
+			preferred_pack_id = m->num_packs_in_base;
+		}
+
+		pack_int_id = m->num_packs_in_base - ctx->compact_from->num_packs_in_base;
+
+		if (fill_pack_from_midx(&ctx->info[pack_int_id++], m,
+					preferred_pack_id) < 0)
+			return -1;
+
+		for (i = m->num_packs_in_base;
+		     i < m->num_packs_in_base + m->num_packs; i++) {
+			if (preferred_pack_id == i)
+				continue;
+
+			if (fill_pack_from_midx(&ctx->info[pack_int_id++], m,
+						i) < 0)
+				return -1;
+		}
+
+		ctx->nr += m->num_packs;
+		m = m->base_midx;
+	}
+
+	ASSERT(ctx->nr == packs_nr);
+
+	return 0;
+}
+
 static struct {
 	const char *non_split;
 	const char *split;
@@ -1075,6 +1168,9 @@ static bool midx_needs_update(struct multi_pack_index *midx, struct write_midx_c
 	if (ctx->incremental)
 		goto out;
 
+	if (ctx->compact)
+		goto out; /* Compaction always requires an update. */
+
 	/*
 	 * Otherwise, we need to verify that the packs covered by the existing
 	 * MIDX match the packs that we already have. The logic to do so is way
@@ -1120,12 +1216,23 @@ out:
 	return needed;
 }
 
+static int midx_hashcmp(const struct multi_pack_index *a,
+			const struct multi_pack_index *b,
+			const struct git_hash_algo *algop)
+{
+	return hashcmp(midx_get_checksum_hash(a), midx_get_checksum_hash(b),
+		       algop);
+}
+
 struct write_midx_opts {
 	struct odb_source *source; /* non-optional */
 
 	struct string_list *packs_to_include;
 	struct string_list *packs_to_drop;
 
+	struct multi_pack_index *compact_from;
+	struct multi_pack_index *compact_to;
+
 	const char *preferred_pack_name;
 	const char *refs_snapshot;
 	unsigned flags;
@@ -1150,6 +1257,7 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	int dropped_packs = 0;
 	int result = -1;
 	const char **keep_hashes = NULL;
+	size_t keep_hashes_nr = 0;
 	struct chunkfile *cf;
 
 	trace2_region_enter("midx", "write_midx_internal", r);
@@ -1162,6 +1270,19 @@ static int write_midx_internal(struct write_midx_opts *opts)
 		die(_("unknown MIDX version: %d"), ctx.version);
 
 	ctx.incremental = !!(opts->flags & MIDX_WRITE_INCREMENTAL);
+	ctx.compact = !!(opts->flags & MIDX_WRITE_COMPACT);
+
+	if (ctx.compact) {
+		if (ctx.version != MIDX_VERSION_V2)
+			die(_("cannot perform MIDX compaction with v1 format"));
+		if (!opts->compact_from)
+			BUG("expected non-NULL 'from' MIDX during compaction");
+		if (!opts->compact_to)
+			BUG("expected non-NULL 'to' MIDX during compaction");
+
+		ctx.compact_from = opts->compact_from;
+		ctx.compact_to = opts->compact_to;
+	}
 
 	if (ctx.incremental)
 		strbuf_addf(&midx_name,
@@ -1189,11 +1310,18 @@ static int write_midx_internal(struct write_midx_opts *opts)
 			 */
 			if (ctx.incremental)
 				ctx.base_midx = m;
-			else if (!opts->packs_to_include)
+			if (!opts->packs_to_include)
 				ctx.m = m;
 		}
 	}
 
+	/*
+	 * If compacting MIDX layer(s) in the range [from, to], then the
+	 * compacted MIDX will share the same base MIDX as 'from'.
+	 */
+	if (ctx.compact)
+		ctx.base_midx = ctx.compact_from->base_midx;
+
 	ctx.nr = 0;
 	ctx.alloc = ctx.m ? ctx.m->num_packs + ctx.m->num_packs_in_base : 16;
 	ctx.info = NULL;
@@ -1210,7 +1338,7 @@ static int write_midx_internal(struct write_midx_opts *opts)
 			ctx.num_multi_pack_indexes_before++;
 			m = m->base_midx;
 		}
-	} else if (ctx.m && fill_packs_from_midx(&ctx)) {
+	} else if (ctx.m && !ctx.compact && fill_packs_from_midx(&ctx)) {
 		goto cleanup;
 	}
 
@@ -1223,9 +1351,18 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	else
 		ctx.progress = NULL;
 
-	ctx.to_include = opts->packs_to_include;
+	if (ctx.compact) {
+		int bitmap_order = 0;
+		if (opts->preferred_pack_name)
+			bitmap_order |= 1;
+		else if (opts->flags & (MIDX_WRITE_REV_INDEX | MIDX_WRITE_BITMAP))
+			bitmap_order |= 1;
 
-	for_each_file_in_pack_dir(opts->source->path, add_pack_to_midx, &ctx);
+		fill_packs_from_midx_range(&ctx, bitmap_order);
+	} else {
+		ctx.to_include = opts->packs_to_include;
+		for_each_file_in_pack_dir(opts->source->path, add_pack_to_midx, &ctx);
+	}
 	stop_progress(&ctx.progress);
 
 	if (!opts->packs_to_drop) {
@@ -1354,12 +1491,19 @@ static int write_midx_internal(struct write_midx_opts *opts)
 			ctx.large_offsets_needed = 1;
 	}
 
-	QSORT(ctx.info, ctx.nr, pack_info_compare);
+	if (ctx.compact) {
+		if (ctx.version != MIDX_VERSION_V2)
+			BUG("performing MIDX compaction with v1 MIDX");
+	} else {
+		QSORT(ctx.info, ctx.nr, pack_info_compare);
+	}
 
 	if (opts->packs_to_drop && opts->packs_to_drop->nr) {
 		size_t drop_index = 0;
 		int missing_drops = 0;
 
+		ASSERT(!ctx.compact);
+
 		for (size_t i = 0;
 		     i < ctx.nr && drop_index < opts->packs_to_drop->nr; i++) {
 			int cmp = strcmp(ctx.info[i].pack_name,
@@ -1391,12 +1535,20 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	 */
 	ALLOC_ARRAY(ctx.pack_perm, ctx.nr);
 	for (size_t i = 0; i < ctx.nr; i++) {
+		uint32_t from = ctx.info[i].orig_pack_int_id;
+		uint32_t to;
+
 		if (ctx.info[i].expired) {
+			to = PACK_EXPIRED;
 			dropped_packs++;
-			ctx.pack_perm[ctx.info[i].orig_pack_int_id] = PACK_EXPIRED;
 		} else {
-			ctx.pack_perm[ctx.info[i].orig_pack_int_id] = i - dropped_packs;
+			to = i - dropped_packs;
 		}
+
+		if (ctx.compact)
+			from -= ctx.compact_from->num_packs_in_base;
+
+		ctx.pack_perm[from] = to;
 	}
 
 	for (size_t i = 0; i < ctx.nr; i++) {
@@ -1542,7 +1694,24 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	if (ctx.num_multi_pack_indexes_before == UINT32_MAX)
 		die(_("too many multi-pack-indexes"));
 
-	CALLOC_ARRAY(keep_hashes, ctx.num_multi_pack_indexes_before + 1);
+	if (ctx.compact) {
+		struct multi_pack_index *m;
+
+		/*
+		 * Keep all MIDX layers excluding those in the range [from, to].
+		 */
+		for (m = ctx.base_midx; m; m = m->base_midx)
+			keep_hashes_nr++;
+		for (m = ctx.m;
+		     m && midx_hashcmp(m, ctx.compact_to, r->hash_algo);
+		     m = m->base_midx)
+			keep_hashes_nr++;
+
+		keep_hashes_nr++; /* include the compacted layer */
+	} else {
+		keep_hashes_nr = ctx.num_multi_pack_indexes_before + 1;
+	}
+	CALLOC_ARRAY(keep_hashes, keep_hashes_nr);
 
 	if (ctx.incremental) {
 		FILE *chainf = fdopen_lock_file(&lk, "w");
@@ -1567,17 +1736,47 @@ static int write_midx_internal(struct write_midx_opts *opts)
 
 		strbuf_release(&final_midx_name);
 
-		keep_hashes[ctx.num_multi_pack_indexes_before] =
-			xstrdup(hash_to_hex_algop(midx_hash, r->hash_algo));
+		if (ctx.compact) {
+			struct multi_pack_index *m;
+			uint32_t num_layers_before_from = 0;
+			uint32_t i;
 
-		for (uint32_t i = 0; i < ctx.num_multi_pack_indexes_before; i++) {
-			uint32_t j = ctx.num_multi_pack_indexes_before - i - 1;
+			for (m = ctx.base_midx; m; m = m->base_midx)
+				num_layers_before_from++;
 
-			keep_hashes[j] = xstrdup(midx_get_checksum_hex(m));
-			m = m->base_midx;
+			m = ctx.base_midx;
+			for (i = 0; i < num_layers_before_from; i++) {
+				uint32_t j = num_layers_before_from - i - 1;
+
+				keep_hashes[j] = xstrdup(midx_get_checksum_hex(m));
+				m = m->base_midx;
+			}
+
+			keep_hashes[i] = xstrdup(hash_to_hex_algop(midx_hash,
+								   r->hash_algo));
+
+			i = 0;
+			for (m = ctx.m;
+			     m && midx_hashcmp(m, ctx.compact_to, r->hash_algo);
+			     m = m->base_midx) {
+				keep_hashes[keep_hashes_nr - i - 1] =
+					xstrdup(midx_get_checksum_hex(m));
+				i++;
+			}
+		} else {
+			keep_hashes[ctx.num_multi_pack_indexes_before] =
+				xstrdup(hash_to_hex_algop(midx_hash,
+							  r->hash_algo));
+
+			for (uint32_t i = 0; i < ctx.num_multi_pack_indexes_before; i++) {
+				uint32_t j = ctx.num_multi_pack_indexes_before - i - 1;
+
+				keep_hashes[j] = xstrdup(midx_get_checksum_hex(m));
+				m = m->base_midx;
+			}
 		}
 
-		for (uint32_t i = 0; i <= ctx.num_multi_pack_indexes_before; i++)
+		for (uint32_t i = 0; i < keep_hashes_nr; i++)
 			fprintf(get_lock_file_fp(&lk), "%s\n", keep_hashes[i]);
 	} else {
 		keep_hashes[ctx.num_multi_pack_indexes_before] =
@@ -1590,8 +1789,7 @@ static int write_midx_internal(struct write_midx_opts *opts)
 	if (commit_lock_file(&lk) < 0)
 		die_errno(_("could not write multi-pack-index"));
 
-	clear_midx_files(opts->source, keep_hashes,
-			 ctx.num_multi_pack_indexes_before + 1,
+	clear_midx_files(opts->source, keep_hashes, keep_hashes_nr,
 			 ctx.incremental);
 	result = 0;
 
@@ -1609,7 +1807,7 @@ cleanup:
 	free(ctx.pack_perm);
 	free(ctx.pack_order);
 	if (keep_hashes) {
-		for (uint32_t i = 0; i <= ctx.num_multi_pack_indexes_before; i++)
+		for (uint32_t i = 0; i < keep_hashes_nr; i++)
 			free((char *)keep_hashes[i]);
 		free(keep_hashes);
 	}
@@ -1651,6 +1849,21 @@ int write_midx_file_only(struct odb_source *source,
 	return write_midx_internal(&opts);
 }
 
+int write_midx_file_compact(struct odb_source *source,
+			    struct multi_pack_index *from,
+			    struct multi_pack_index *to,
+			    unsigned flags)
+{
+	struct write_midx_opts opts = {
+		.source = source,
+		.compact_from = from,
+		.compact_to = to,
+		.flags = flags | MIDX_WRITE_COMPACT,
+	};
+
+	return write_midx_internal(&opts);
+}
+
 int expire_midx_packs(struct odb_source *source, unsigned flags)
 {
 	uint32_t i, *count, result = 0;
diff --git a/midx.h b/midx.h
index aa99a6cb21..08f3728e52 100644
--- a/midx.h
+++ b/midx.h
@@ -82,6 +82,7 @@ struct multi_pack_index {
 #define MIDX_WRITE_BITMAP_HASH_CACHE (1 << 3)
 #define MIDX_WRITE_BITMAP_LOOKUP_TABLE (1 << 4)
 #define MIDX_WRITE_INCREMENTAL (1 << 5)
+#define MIDX_WRITE_COMPACT (1 << 6)
 
 #define MIDX_EXT_REV "rev"
 #define MIDX_EXT_BITMAP "bitmap"
@@ -131,6 +132,10 @@ int write_midx_file_only(struct odb_source *source,
 			 struct string_list *packs_to_include,
 			 const char *preferred_pack_name,
 			 const char *refs_snapshot, unsigned flags);
+int write_midx_file_compact(struct odb_source *source,
+			    struct multi_pack_index *from,
+			    struct multi_pack_index *to,
+			    unsigned flags);
 void clear_midx_file(struct repository *r);
 int verify_midx_file(struct odb_source *source, unsigned flags);
 int expire_midx_packs(struct odb_source *source, unsigned flags);
diff --git a/t/meson.build b/t/meson.build
index 459c52a489..5393322a8d 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -614,6 +614,7 @@ integration_tests = [
   't5332-multi-pack-reuse.sh',
   't5333-pseudo-merge-bitmaps.sh',
   't5334-incremental-multi-pack-index.sh',
+  't5335-compact-multi-pack-index.sh',
   't5351-unpack-large-objects.sh',
   't5400-send-pack.sh',
   't5401-update-hooks.sh',
diff --git a/t/t5335-compact-multi-pack-index.sh b/t/t5335-compact-multi-pack-index.sh
new file mode 100755
index 0000000000..797ae05c3b
--- /dev/null
+++ b/t/t5335-compact-multi-pack-index.sh
@@ -0,0 +1,175 @@
+#!/bin/sh
+
+test_description='multi-pack-index compaction'
+
+. ./test-lib.sh
+
+GIT_TEST_MULTI_PACK_INDEX=0
+GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0
+GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL=0
+
+objdir=.git/objects
+packdir=$objdir/pack
+midxdir=$packdir/multi-pack-index.d
+midx_chain=$midxdir/multi-pack-index-chain
+
+nth_line() {
+	local n="$1"
+	shift
+	awk "NR==$n" "$@"
+}
+
+write_packs () {
+	for c in "$@"
+	do
+		test_commit "$c" &&
+
+		git pack-objects --all --unpacked $packdir/pack-$c &&
+		git prune-packed &&
+
+		git multi-pack-index write --incremental --bitmap || return 1
+	done
+}
+
+test_midx_layer_packs () {
+	local checksum="$1" &&
+	shift &&
+
+	test-tool read-midx $objdir "$checksum" >out &&
+
+	printf "%s\n" "$@" >expect &&
+	# NOTE: do *not* pipe through sort here, we want to ensure the
+	# order of packs is preserved during compaction.
+	grep "^pack-" out | cut -d"-" -f2 >actual &&
+
+	test_cmp expect actual
+}
+
+test_midx_layer_object_uniqueness () {
+	: >objs.all
+	while read layer
+	do
+		test-tool read-midx --show-objects $objdir "$layer" >out &&
+		grep "\.pack$" out | cut -d" " -f1 | sort >objs.layer &&
+		test_stdout_line_count = 0 comm -12 objs.all objs.layer &&
+		cat objs.all objs.layer | sort >objs.tmp &&
+		mv objs.tmp objs.all || return 1
+	done <$midx_chain
+}
+
+test_expect_success 'MIDX compaction with lex-ordered pack names' '
+	git init midx-compact-lex-order &&
+	(
+		cd midx-compact-lex-order &&
+
+		git config maintenance.auto false &&
+
+		write_packs A B C D E &&
+		test_line_count = 5 $midx_chain &&
+
+		git multi-pack-index compact --incremental \
+			"$(nth_line 2 "$midx_chain")" \
+			"$(nth_line 4 "$midx_chain")" &&
+		test_line_count = 3 $midx_chain &&
+
+		test_midx_layer_packs "$(nth_line 1 "$midx_chain")" A &&
+		test_midx_layer_packs "$(nth_line 2 "$midx_chain")" B C D &&
+		test_midx_layer_packs "$(nth_line 3 "$midx_chain")" E &&
+
+		test_midx_layer_object_uniqueness
+	)
+'
+
+test_expect_success 'MIDX compaction with non-lex-ordered pack names' '
+	git init midx-compact-non-lex-order &&
+	(
+		cd midx-compact-non-lex-order &&
+
+		git config maintenance.auto false &&
+
+		write_packs D C A B E &&
+		test_line_count = 5 $midx_chain &&
+
+		git multi-pack-index compact --incremental \
+			"$(nth_line 2 "$midx_chain")" \
+			"$(nth_line 4 "$midx_chain")" &&
+		test_line_count = 3 $midx_chain &&
+
+		test_midx_layer_packs "$(nth_line 1 "$midx_chain")" D &&
+		test_midx_layer_packs "$(nth_line 2 "$midx_chain")" C A B &&
+		test_midx_layer_packs "$(nth_line 3 "$midx_chain")" E &&
+
+		test_midx_layer_object_uniqueness
+	)
+'
+
+test_expect_success 'setup for bogus MIDX compaction scenarios' '
+	git init midx-compact-bogus &&
+	(
+		cd midx-compact-bogus &&
+
+		git config maintenance.auto false &&
+
+		write_packs A B C
+	)
+'
+
+test_expect_success 'MIDX compaction with missing endpoints' '
+	(
+		cd midx-compact-bogus &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"<missing>" "<missing>" 2>err &&
+		test_grep "could not find MIDX: <missing>" err &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"<missing>" "$(nth_line 2 "$midx_chain")" 2>err &&
+		test_grep "could not find MIDX: <missing>" err &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"$(nth_line 2 "$midx_chain")" "<missing>" 2>err &&
+		test_grep "could not find MIDX: <missing>" err
+	)
+'
+
+test_expect_success 'MIDX compaction with reversed endpoints' '
+	(
+		cd midx-compact-bogus &&
+
+		from="$(nth_line 3 "$midx_chain")" &&
+		to="$(nth_line 1 "$midx_chain")" &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"$from" "$to" 2>err &&
+
+		test_grep "MIDX $from must be an ancestor of $to" err
+	)
+'
+
+test_expect_success 'MIDX compaction with identical endpoints' '
+	(
+		cd midx-compact-bogus &&
+
+		from="$(nth_line 3 "$midx_chain")" &&
+		to="$(nth_line 3 "$midx_chain")" &&
+
+		test_must_fail git multi-pack-index compact --incremental \
+			"$from" "$to" 2>err &&
+
+		test_grep "MIDX compaction endpoints must be unique" err
+	)
+'
+
+test_expect_success 'MIDX compaction with midx.version=1' '
+	(
+		cd midx-compact-bogus &&
+
+		test_must_fail git -c midx.version=1 multi-pack-index compact \
+			"$(nth_line 1 "$midx_chain")" \
+			"$(nth_line 2 "$midx_chain")" 2>err &&
+
+		test_grep "fatal: cannot perform MIDX compaction with v1 format" err
+	)
+'
+
+test_done