Subject: [GSoC RFC PATCH v3 3/5] repo-info: add the field references.format

From: Lucas Seiki Oshiro <[email-masked]>
Date: Sun, 6 Jul 2025 20:19:36 -0300

This commit is part of the series that introduce the new command
git-repo-info.

The flag `--show-ref-format` from git-rev-parse is used for retrieving
the reference format (i.e. `files` or `reftable`). This way, it is
used for querying repository information, fitting in the purpose of
git-repo-info.

Then, add a new field `references.format` to the repo-info command
containing that information.

Helped-by: Phillip Wood <[email-masked]>
Helped-by: Junio C Hamano <[email-masked]>
Mentored-by: Karthik Nayak <[email-masked]>
Mentored-by: Patrick Steinhardt <[email-masked]>
Signed-off-by: Lucas Seiki Oshiro <[email-masked]>
---
 Documentation/git-repo-info.adoc |   4 ++
 builtin/repo-info.c              | 105 ++++++++++++++++++++++++++++++-
 t/meson.build                    |   1 +
 t/t1900-repo-info.sh             |  64 +++++++++++++++++++
 4 files changed, 171 insertions(+), 3 deletions(-)
 create mode 100755 t/t1900-repo-info.sh

diff --git a/Documentation/git-repo-info.adoc b/Documentation/git-repo-info.adoc
index bf1d391482..dd221b236e 100644
--- a/Documentation/git-repo-info.adoc
+++ b/Documentation/git-repo-info.adoc
@@ -66,6 +66,10 @@ CATEGORIES AND FIELDS
 The set of data that `git repo-info` can return is divided into
 categories. Each category is composed by one or more fields.
 
+`references`::
+Reference-related data:
+* `format`: the reference storage format, either `files` or `reftable`.
+
 SEE ALSO
 --------
 linkgit:git-rev-parse[1]
diff --git a/builtin/repo-info.c b/builtin/repo-info.c
index cb4785169f..98a0d83d51 100644
--- a/builtin/repo-info.c
+++ b/builtin/repo-info.c
@@ -1,20 +1,39 @@
 #include "builtin.h"
 #include "json-writer.h"
 #include "parse-options.h"
+#include "refs.h"
 
 enum output_format {
 	FORMAT_JSON,
 	FORMAT_NULL_TERMINATED,
 };
 
+enum repo_info_category {
+	CATEGORY_REFERENCES = 1 << 0,
+};
+
+enum repo_info_references_field {
+	FIELD_REFERENCES_FORMAT = 1 << 0,
+};
+
+struct repo_info_field {
+	enum repo_info_category category;
+	union {
+		enum repo_info_references_field references;
+	} u;
+};
+
 struct repo_info {
 	struct repository *repo;
 	enum output_format format;
+	size_t fields_nr;
+	struct repo_info_field *fields;
 };
 
 static void repo_info_init(struct repo_info *repo_info,
 			   struct repository *repo,
-			   const char *format)
+			   const char *format,
+			   int argc, const char **argv)
 {
 	repo_info->repo = repo;
 
@@ -24,15 +43,93 @@ static void repo_info_init(struct repo_info *repo_info,
 		repo_info->format = FORMAT_NULL_TERMINATED;
 	else
 		die("invalid format %s", format);
+
+	repo_info->fields_nr = argc;
+	ALLOC_ARRAY(repo_info->fields, argc);
+
+	for (int i = 0; i < argc; i++) {
+		const char *arg = argv[i];
+		struct repo_info_field *field = repo_info->fields + i;
+		if (!strcmp(arg, "references.format")) {
+			field->category = CATEGORY_REFERENCES;
+			field->u.references = FIELD_REFERENCES_FORMAT;
+		} else {
+			die("invalid field '%s'", arg);
+		}
+	}
+}
+
+static void repo_info_release(struct repo_info *repo_info)
+{
+	free(repo_info->fields);
 }
 
-static void repo_info_print_json(struct repo_info *repo_info UNUSED)
+static void append_null_terminated_field(struct strbuf *buf,
+					 struct repo_info *repo_info,
+					 struct repo_info_field *field)
+{
+	struct repository *repo = repo_info->repo;
+
+	switch (field->category) {
+	case CATEGORY_REFERENCES:
+		strbuf_addstr(buf, "references.");
+		switch (field->u.references) {
+		case FIELD_REFERENCES_FORMAT:
+			strbuf_addstr(buf, "format\n");
+			strbuf_addstr(buf, ref_storage_format_to_name(
+						   repo->ref_storage_format));
+			break;
+		}
+		break;
+	}
+
+	strbuf_addch(buf, '\0');
+}
+
+static void repo_info_print_null_terminated(struct repo_info *repo_info)
+{
+	struct strbuf buf;
+
+	strbuf_init(&buf, 256);
+
+	for (size_t i = 0; i < repo_info->fields_nr; i++) {
+		struct repo_info_field *field = &repo_info->fields[i];
+		append_null_terminated_field(&buf, repo_info, field);
+	}
+
+	fwrite(buf.buf, 1, buf.len, stdout);
+	strbuf_release(&buf);
+}
+
+static void repo_info_print_json(struct repo_info *repo_info)
 {
 	struct json_writer jw;
+	unsigned int categories = 0;
+	unsigned int references_fields = 0;
+	struct repository *repo = repo_info->repo;
+
+	for (size_t i = 0; i < repo_info->fields_nr; i++) {
+		struct repo_info_field *field = repo_info->fields + i;
+		categories |= field->category;
+		switch (field->category) {
+		case CATEGORY_REFERENCES:
+			references_fields |= field->u.references;
+			break;
+		}
+	}
 
 	jw_init(&jw);
 
 	jw_object_begin(&jw, 1);
+	if (categories & CATEGORY_REFERENCES) {
+		jw_object_inline_begin_object(&jw, "references");
+		if (references_fields & FIELD_REFERENCES_FORMAT) {
+			const char *format_name = ref_storage_format_to_name(
+				repo->ref_storage_format);
+			jw_object_string(&jw, "format", format_name);
+		}
+		jw_end(&jw);
+	}
 	jw_end(&jw);
 
 	puts(jw.json.buf);
@@ -46,6 +143,7 @@ static void repo_info_print(struct repo_info *repo_info)
 		repo_info_print_json(repo_info);
 		break;
 	case FORMAT_NULL_TERMINATED:
+		repo_info_print_null_terminated(repo_info);
 		break;
 	default:
 		BUG("%d: not a valid repo-info format", repo_info->format);
@@ -71,8 +169,9 @@ int cmd_repo_info(int argc,
 
 	argc = parse_options(argc, argv, prefix, options, repo_info_usage,
 			     0);
-	repo_info_init(&repo_info, repo, format);
+	repo_info_init(&repo_info, repo, format, argc, argv);
 	repo_info_print(&repo_info);
+	repo_info_release(&repo_info);
 
 	return 0;
 }
diff --git a/t/meson.build b/t/meson.build
index 6d7fe6b117..e2c9393189 100644
--- a/t/meson.build
+++ b/t/meson.build
@@ -245,6 +245,7 @@ integration_tests = [
   't1700-split-index.sh',
   't1701-racy-split-index.sh',
   't1800-hook.sh',
+  't1900-repo-info.sh',
   't2000-conflict-when-checking-files-out.sh',
   't2002-checkout-cache-u.sh',
   't2003-checkout-cache-mkdir.sh',
diff --git a/t/t1900-repo-info.sh b/t/t1900-repo-info.sh
new file mode 100755
index 0000000000..2af9d1d9c3
--- /dev/null
+++ b/t/t1900-repo-info.sh
@@ -0,0 +1,64 @@
+#!/bin/sh
+
+test_description='test git repo-info'
+
+. ./test-lib.sh
+
+parse_json () {
+	tr '\n' ' ' | "$PERL_PATH" "$TEST_DIRECTORY/t0019/parse_json.perl"
+}
+
+test_lazy_prereq PERLJSON '
+	perl -MJSON -e "exit 0"
+'
+
+# Test if a field is correctly returned in both null-terminated and json formats.
+#
+# Usage: test_repo_info <label> <init command> <key> <expected value>
+#
+# Arguments:
+#   label: the label of the test
+#   init command: a command that creates a repository called 'repo', configured
+#      accordingly to what is being tested
+#   key: the key of the field that is being tested
+#   expected value: the value that the field should contain
+test_repo_info () {
+        label=$1
+        init_command=$2
+        key=$3
+        expected_value=$4
+
+        test_expect_success PERLJSON "json: $label" '
+		test_when_finished "rm -rf repo" &&
+		eval "$init_command" &&
+		echo "$expected_value" >expect &&
+		git -C repo repo-info "$key" >output &&
+		parse_json <output >parsed &&
+		grep -F "row[0].$key" parsed | cut -d " " -f 2 >value &&
+		sed -n -e "/row[0].$key/{
+			s/^[^ ]* //
+			s/^1\$/true/
+			s/^0\$/false/
+			p;
+			}" parsed >actual &&
+		sed "s/^0$/false/" <value| sed "s/^1$/true/" >actual &&
+		test_cmp expect actual
+        '
+
+        test_expect_success "null-terminated: $label" '
+		test_when_finished "rm -rf repo" &&
+		eval "$init_command" &&
+		echo "$expected_value" | lf_to_nul >expect &&
+		git -C repo repo-info --format=null-terminated "$key" >output &&
+		tail -n 1 output >actual &&
+		test_cmp expect actual
+	'
+}
+
+test_repo_info 'ref format files is retrieved correctly' '
+	git init --ref-format=files repo' 'references.format' 'files'
+
+test_repo_info 'ref format reftable is retrieved correctly' '
+	git init --ref-format=reftable repo' 'references.format' 'reftable'
+
+test_done
-- 
2.39.5 (Apple Git-154)