make the pack index version configurable

It is a good idea to use pack index version 2 all the time since it has
proper protection against propagation of certain pack corruptions when
repacking which is not possible with index version 1, as demonstrated
in test t5302.

Hence this config option.

The default is still pack index version 1.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -661,6 +661,15 @@ pack.threads::
 	machines. The required amount of memory for the delta search window
 	is however multiplied by the number of threads.
 
+pack.indexVersion::
+	Specify the default pack index version.  Valid values are 1 for
+	legacy pack index used by Git versions prior to 1.5.2, and 2 for
+	the new pack index with capabilities for packs larger than 4 GB
+	as well as proper protection against the repacking of corrupted
+	packs.  Version 2 is selected and this config option ignored
+	whenever the corresponding pack is larger than 2 GB.  Otherwise
+	the default is 1.
+
 pull.octopus::
 	The default merge strategy to use when pulling multiple branches
 	at once.

builtin-pack-objects.c

@@ -1773,6 +1773,12 @@ static int git_pack_config(const char *k, const char *v)
 #endif
 		return 0;
 	}
+	if (!strcmp(k, "pack.indexversion")) {
+		pack_idx_default_version = git_config_int(k, v);
+		if (pack_idx_default_version > 2)
+			die("bad pack.indexversion=%d", pack_idx_default_version);
+		return 0;
+	}
 	return git_default_config(k, v);
 }
 

index-pack.c

@@ -683,6 +683,17 @@ static void final(const char *final_pack_name, const char *curr_pack_name,
 	}
 }
 
+static int git_index_pack_config(const char *k, const char *v)
+{
+	if (!strcmp(k, "pack.indexversion")) {
+		pack_idx_default_version = git_config_int(k, v);
+		if (pack_idx_default_version > 2)
+			die("bad pack.indexversion=%d", pack_idx_default_version);
+		return 0;
+	}
+	return git_default_config(k, v);
+}
+
 int main(int argc, char **argv)
 {
 	int i, fix_thin_pack = 0;
@@ -693,6 +704,8 @@ int main(int argc, char **argv)
 	struct pack_idx_entry **idx_objects;
 	unsigned char sha1[20];
 
+	git_config(git_index_pack_config);
+
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];