midx: load multi-pack indices via their source

To load a multi-pack index the caller is expected to pass both the
repository and the object directory where the multi-pack index is
located. While this works, this layout has a couple of downsides:

  - We need to pass in information reduntant with the owning source,
    namely its object directory and whether the source is local or not.

  - We don't have access to the source when loading the multi-pack
    index. If we had that access, we could store a pointer to the owning
    source in the MIDX and thus deduplicate some information.

  - Multi-pack indices are inherently specific to the object source and
    its format. With the goal of pluggable object backends in mind we
    will eventually want the backends to own the logic of reading and
    writing multi-pack indices. Making the logic work on top of object
    sources is a step into that direction.

Refactor loading of multi-pack indices accordingly.

This surfaces one small problem though: git-multi-pack-index(1) and our
MIDX test helper both know to read and write multi-pack-indices located
in a different object directory. This issue is addressed by adding the
user-provided object directory as an in-memory alternate.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/builtin/multi-pack-index.c b/builtin/multi-pack-index.c
index aa25b06f9d..e4a9305af3 100644
--- a/builtin/multi-pack-index.c
+++ b/builtin/multi-pack-index.c
@@ -64,12 +64,20 @@ static int parse_object_dir(const struct option *opt, const char *arg,
 	char **value = opt->value;
 	free(*value);
 	if (unset)
-		*value = xstrdup(repo_get_object_directory(the_repository));
+		*value = xstrdup(the_repository->objects->sources->path);
 	else
 		*value = real_pathdup(arg, 1);
 	return 0;
 }
 
+static struct odb_source *handle_object_dir_option(struct repository *repo)
+{
+	struct odb_source *source = odb_find_source(repo->objects, opts.object_dir);
+	if (!source)
+		source = odb_add_to_alternates_memory(repo->objects, opts.object_dir);
+	return source;
+}
+
 static struct option common_opts[] = {
 	OPT_CALLBACK(0, "object-dir", &opts.object_dir,
 	  N_("directory"),
@@ -157,6 +165,7 @@ static int cmd_multi_pack_index_write(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_write_usage,
 				   options);
+	handle_object_dir_option(repo);
 
 	FREE_AND_NULL(options);
 
@@ -193,6 +202,8 @@ static int cmd_multi_pack_index_verify(int argc, const char **argv,
 			N_("force progress reporting"), MIDX_PROGRESS),
 		OPT_END(),
 	};
+	struct odb_source *source;
+
 	options = add_common_options(builtin_multi_pack_index_verify_options);
 
 	trace2_cmd_mode(argv[0]);
@@ -205,10 +216,11 @@ static int cmd_multi_pack_index_verify(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_verify_usage,
 				   options);
+	source = handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
-	return verify_midx_file(the_repository, opts.object_dir, opts.flags);
+	return verify_midx_file(source, opts.flags);
 }
 
 static int cmd_multi_pack_index_expire(int argc, const char **argv,
@@ -233,6 +245,7 @@ static int cmd_multi_pack_index_expire(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_expire_usage,
 				   options);
+	handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);
 
@@ -265,6 +278,7 @@ static int cmd_multi_pack_index_repack(int argc, const char **argv,
 	if (argc)
 		usage_with_options(builtin_multi_pack_index_repack_usage,
 				   options);
+	handle_object_dir_option(the_repository);
 
 	FREE_AND_NULL(options);