setup: make ref storage format configurable via config

Similar to the preceding commit, introduce a new "init.defaultRefFormat"
config that allows the user to globally set the ref storage format used
by newly created repositories.

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

Documentation/config/init.txt

@@ -13,3 +13,8 @@ endif::[]
 	`--object-format=` in linkgit:git-init[1]. Both the command line option
 	and the `GIT_DEFAULT_HASH` environment variable take precedence over
 	this config.
+`init.defaultRefFormat`::
+	Allows overriding the default ref storage format for new repositories.
+	See `--ref-format=` in linkgit:git-init[1]. Both the command line
+	option and the `GIT_DEFAULT_REF_FORMAT` environment variable take
+	precedence over this config.

setup.c

@@ -2286,6 +2286,7 @@ static void separate_git_dir(const char *git_dir, const char *git_link)
 
 struct default_format_config {
 	int hash;
+	enum ref_storage_format ref_format;
 };
 
 static int read_default_format_config(const char *key, const char *value,
@@ -2306,6 +2307,16 @@ static int read_default_format_config(const char *key, const char *value,
 		goto out;
 	}
 
+	if (!strcmp(key, "init.defaultrefformat")) {
+		ret = git_config_string(&str, key, value);
+		if (ret)
+			goto out;
+		cfg->ref_format = ref_storage_format_by_name(str);
+		if (cfg->ref_format == REF_STORAGE_FORMAT_UNKNOWN)
+			warning(_("unknown ref storage format '%s'"), str);
+		goto out;
+	}
+
 	ret = 0;
 out:
 	free(str);
@@ -2317,6 +2328,7 @@ static void repository_format_configure(struct repository_format *repo_fmt,
 {
 	struct default_format_config cfg = {
 		.hash = GIT_HASH_UNKNOWN,
+		.ref_format = REF_STORAGE_FORMAT_UNKNOWN,
 	};
 	struct config_options opts = {
 		.respect_includes = 1,
@@ -2359,6 +2371,8 @@ static void repository_format_configure(struct repository_format *repo_fmt,
 		if (ref_format == REF_STORAGE_FORMAT_UNKNOWN)
 			die(_("unknown ref storage format '%s'"), env);
 		repo_fmt->ref_storage_format = ref_format;
+	} else if (cfg.ref_format != REF_STORAGE_FORMAT_UNKNOWN) {
+		repo_fmt->ref_storage_format = cfg.ref_format;
 	}
 	repo_set_ref_storage_format(the_repository, repo_fmt->ref_storage_format);
 }

t/t0001-init.sh

@@ -620,6 +620,19 @@ test_expect_success 'init with GIT_DEFAULT_REF_FORMAT=garbage' '
 	test_cmp expect err
 '
 
+test_expect_success 'init warns about invalid init.defaultRefFormat' '
+	test_when_finished "rm -rf repo" &&
+	test_config_global init.defaultRefFormat garbage &&
+
+	echo "warning: unknown ref storage format ${SQ}garbage${SQ}" >expect &&
+	git init repo 2>err &&
+	test_cmp expect err &&
+
+	git -C repo rev-parse --show-ref-format >actual &&
+	echo $GIT_DEFAULT_REF_FORMAT >expected &&
+	test_cmp expected actual
+'
+
 backends="files reftable"
 for format in $backends
 do
@@ -650,6 +663,27 @@ do
 		git -C refformat rev-parse --show-ref-format >actual &&
 		test_cmp expect actual
 	'
+
+	test_expect_success "init with init.defaultRefFormat=$format" '
+		test_when_finished "rm -rf refformat" &&
+		test_config_global init.defaultRefFormat $format &&
+		(
+			sane_unset GIT_DEFAULT_REF_FORMAT &&
+			git init refformat
+		) &&
+
+		echo $format >expect &&
+		git -C refformat rev-parse --show-ref-format >actual &&
+		test_cmp expect actual
+	'
+
+	test_expect_success "--ref-format=$format overrides GIT_DEFAULT_REF_FORMAT" '
+		test_when_finished "rm -rf refformat" &&
+		GIT_DEFAULT_REF_FORMAT=garbage git init --ref-format=$format refformat &&
+		echo $format >expect &&
+		git -C refformat rev-parse --show-ref-format >actual &&
+		test_cmp expect actual
+	'
 done
 
 test_expect_success "--ref-format= overrides GIT_DEFAULT_REF_FORMAT" '
@@ -660,6 +694,16 @@ test_expect_success "--ref-format= overrides GIT_DEFAULT_REF_FORMAT" '
 	test_cmp expect actual
 '
 
+test_expect_success "GIT_DEFAULT_REF_FORMAT= overrides init.defaultRefFormat" '
+	test_when_finished "rm -rf refformat" &&
+	test_config_global init.defaultRefFormat files &&
+
+	GIT_DEFAULT_REF_FORMAT=reftable git init refformat &&
+	echo reftable >expect &&
+	git -C refformat rev-parse --show-ref-format >actual &&
+	test_cmp expect actual
+'
+
 for from_format in $backends
 do
 	test_expect_success "re-init with same format ($from_format)" '