multi-pack-index: add 'verify' verb

The multi-pack-index builtin writes multi-pack-index files, and
uses a 'write' verb to do so. Add a 'verify' verb that checks this
file matches the contents of the pack-indexes it replaces.

The current implementation is a no-op, but will be extended in
small increments in later commits.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-multi-pack-index.txt

@@ -27,6 +27,10 @@ write::
 	When given as the verb, write a new MIDX file to
 	`<dir>/packs/multi-pack-index`.
 
+verify::
+	When given as the verb, verify the contents of the MIDX file
+	at `<dir>/packs/multi-pack-index`.
+
 
 EXAMPLES
 --------
@@ -43,6 +47,12 @@ $ git multi-pack-index write
 $ git multi-pack-index --object-dir <alt> write
 -----------------------------------------------
 
+* Verify the MIDX file for the packfiles in the current .git folder.
++
+-----------------------------------------------
+$ git multi-pack-index verify
+-----------------------------------------------
+
 
 SEE ALSO
 --------

builtin/multi-pack-index.c

@@ -5,7 +5,7 @@
 #include "midx.h"
 
 static char const * const builtin_multi_pack_index_usage[] = {
-	N_("git multi-pack-index [--object-dir=<dir>] write"),
+	N_("git multi-pack-index [--object-dir=<dir>] (write|verify)"),
 	NULL
 };
 
@@ -42,6 +42,8 @@ int cmd_multi_pack_index(int argc, const char **argv,
 
 	if (!strcmp(argv[0], "write"))
 		return write_midx_file(opts.object_dir);
+	if (!strcmp(argv[0], "verify"))
+		return verify_midx_file(opts.object_dir);
 
 	die(_("unrecognized verb: %s"), argv[0]);
 }

midx.c

@@ -928,3 +928,16 @@ void clear_midx_file(const char *object_dir)
 
 	free(midx);
 }
+
+static int verify_midx_error;
+
+int verify_midx_file(const char *object_dir)
+{
+	struct multi_pack_index *m = load_multi_pack_index(object_dir, 1);
+	verify_midx_error = 0;
+
+	if (!m)
+		return 0;
+
+	return verify_midx_error;
+}

midx.h

@@ -43,5 +43,6 @@ int prepare_multi_pack_index_one(struct repository *r, const char *object_dir, i
 
 int write_midx_file(const char *object_dir);
 void clear_midx_file(const char *object_dir);
+int verify_midx_file(const char *object_dir);
 
 #endif

t/t5319-multi-pack-index.sh

@@ -150,6 +150,10 @@ test_expect_success 'write midx with twelve packs' '
 
 compare_results_with_midx "twelve packs"
 
+test_expect_success 'verify multi-pack-index success' '
+	git multi-pack-index verify --object-dir=$objdir
+'
+
 test_expect_success 'repack removes multi-pack-index' '
 	test_path_is_file $objdir/pack/multi-pack-index &&
 	git repack -adf &&
@@ -214,4 +218,8 @@ test_expect_success 'force some 64-bit offsets with pack-objects' '
 	midx_read_expect 1 63 5 objects64 " large-offsets"
 '
 
+test_expect_success 'verify multi-pack-index with 64-bit offsets' '
+	git multi-pack-index verify --object-dir=objects64
+'
+
 test_done