repo: add the field objects.format

The flag `--show-object-format` from git-rev-parse is used for
retrieving the object storage format. This way, it is used for
querying repository metadata, fitting in the purpose of git-repo-info.

Add a new field `objects.format` to the git-repo-info subcommand
containing that information.

Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Mentored-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: lucasoshiro

Documentation/git-repo.adoc

@@ -55,6 +55,9 @@ values that they return:
 `layout.shallow`::
 	`true` if this is a shallow repository, otherwise `false`.
 
+`object.format`::
+	The object format (hash algorithm) used in the repository.
+
 `references.format`::
 	The reference storage format. The valid values are:
 +

builtin/repo.c

@@ -38,6 +38,12 @@ static int get_layout_shallow(struct repository *repo, struct strbuf *buf)
 	return 0;
 }
 
+static int get_object_format(struct repository *repo, struct strbuf *buf)
+{
+	strbuf_addstr(buf, repo->hash_algo->name);
+	return 0;
+}
+
 static int get_references_format(struct repository *repo, struct strbuf *buf)
 {
 	strbuf_addstr(buf,
@@ -49,6 +55,7 @@ static int get_references_format(struct repository *repo, struct strbuf *buf)
 static const struct field repo_info_fields[] = {
 	{ "layout.bare", get_layout_bare },
 	{ "layout.shallow", get_layout_shallow },
+	{ "object.format", get_object_format },
 	{ "references.format", get_references_format },
 };
 

t/t1900-repo.sh

@@ -63,6 +63,12 @@ test_expect_success 'setup remote' '
 test_repo_info 'shallow repository = true is retrieved correctly' \
 	'git clone --depth 1 "file://$PWD/remote"' 'shallow' 'layout.shallow' 'true'
 
+test_repo_info 'object.format = sha1 is retrieved correctly' \
+	'git init --object-format=sha1' 'sha1' 'object.format' 'sha1'
+
+test_repo_info 'object.format = sha256 is retrieved correctly' \
+	'git init --object-format=sha256' 'sha256' 'object.format' 'sha256'
+
 test_expect_success 'values returned in order requested' '
 	cat >expect <<-\EOF &&
 	layout.bare=false