repo: add new flag --keys to git-repo-info

If the user wants to find what are the available keys, they need to
either check the documentation or to ask for all the key-value pairs
by using --all.

Add a new flag --keys for listing only the available keys without
listing the values.

Signed-off-by: Lucas Seiki Oshiro <lucasseikioshiro@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: lucasoshiro

Documentation/git-repo.adoc

@@ -9,6 +9,7 @@ SYNOPSIS
 --------
 [synopsis]
 git repo info [--format=(lines|nul) | -z] [--all | <key>...]
+git repo info --keys [--format=(lines|nul) | -z]
 git repo structure [--format=(table|lines|nul) | -z]
 
 DESCRIPTION
@@ -45,6 +46,16 @@ supported:
 +
 `-z` is an alias for `--format=nul`.
 
+`info --keys [--format=(lines|nul) | -z]`::
+	List all the available keys, one per line. The output format can be chosen
+	through the flag `--format`. The following formats are supported:
++
+`lines`:::
+	Output the keys one per line. This is the default.
+
+`nul`:::
+	Similar to `lines`, but using a _NUL_ character after each value.
+
 `structure [--format=(table|lines|nul) | -z]`::
 	Retrieve statistics about the current repository structure. The
 	following kinds of information are reported:

builtin/repo.c

@@ -18,6 +18,7 @@
 
 static const char *const repo_usage[] = {
 	"git repo info [--format=(lines|nul) | -z] [--all | <key>...]",
+	"git repo info --keys [--format=(lines|nul) | -z]",
 	"git repo structure [--format=(table|lines|nul) | -z]",
 	NULL
 };
@@ -148,6 +149,29 @@ static int print_all_fields(struct repository *repo,
 	return 0;
 }
 
+static int print_keys(enum output_format format)
+{
+	char sep;
+
+	switch (format) {
+	case FORMAT_NEWLINE_TERMINATED:
+		sep = '\n';
+		break;
+	case FORMAT_NUL_TERMINATED:
+		sep = '\0';
+		break;
+	default:
+		die(_("--keys can only be used with --format=lines or --format=nul"));
+	}
+
+	for (size_t i = 0; i < ARRAY_SIZE(repo_info_fields); i++) {
+		const struct field *field = &repo_info_fields[i];
+		printf("%s%c", field->key, sep);
+	}
+
+	return 0;
+}
+
 static int parse_format_cb(const struct option *opt,
 			   const char *arg, int unset UNUSED)
 {
@@ -172,6 +196,7 @@ static int cmd_repo_info(int argc, const char **argv, const char *prefix,
 {
 	enum output_format format = FORMAT_NEWLINE_TERMINATED;
 	int all_keys = 0;
+	int show_keys = 0;
 	struct option options[] = {
 		OPT_CALLBACK_F(0, "format", &format, N_("format"),
 			       N_("output format"),
@@ -181,11 +206,18 @@ static int cmd_repo_info(int argc, const char **argv, const char *prefix,
 			       PARSE_OPT_NONEG | PARSE_OPT_NOARG,
 			       parse_format_cb),
 		OPT_BOOL(0, "all", &all_keys, N_("print all keys/values")),
+		OPT_BOOL(0, "keys", &show_keys, N_("show keys")),
 		OPT_END()
 	};
 
 	argc = parse_options(argc, argv, prefix, options, repo_usage, 0);
 
+	if (show_keys && (all_keys || argc))
+		die(_("--keys cannot be used with a <key> or --all"));
+
+	if (show_keys)
+		return print_keys(format);
+
 	if (format != FORMAT_NEWLINE_TERMINATED && format != FORMAT_NUL_TERMINATED)
 		die(_("unsupported output format"));
 

t/t1900-repo.sh

@@ -4,15 +4,6 @@ test_description='test git repo-info'
 
 . ./test-lib.sh
 
-# git-repo-info keys. It must contain the same keys listed in the const
-# repo_info_fields, in lexicographical order.
-REPO_INFO_KEYS='
-	layout.bare
-	layout.shallow
-	object.format
-	references.format
-'
-
 # Test whether a key-value pair is correctly returned
 #
 # Usage: test_repo_info <label> <init command> <repo_name> <key> <expected value>
@@ -119,8 +110,8 @@ test_expect_success 'git repo info uses the last requested format' '
 	test_cmp expected actual
 '
 
-test_expect_success 'git repo info --all returns all key-value pairs' '
-	git repo info $REPO_INFO_KEYS >expect &&
+test_expect_success 'git repo info --all and git repo info $(git repo info --keys) output the same data' '
+	git repo info $(git repo info --keys) >expect &&
 	git repo info --all >actual &&
 	test_cmp expect actual
 '
@@ -131,4 +122,31 @@ test_expect_success 'git repo info --all <key> aborts' '
 	test_cmp expect actual
 '
 
+test_expect_success 'git repo info --keys --format=nul uses nul-terminated output' '
+	git repo info --keys --format=lines >lines &&
+	lf_to_nul <lines >expect &&
+	git repo info --keys --format=nul >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git repo info --keys aborts when using --format other than lines or nul' '
+	echo "fatal: --keys can only be used with --format=lines or --format=nul" >expect &&
+	test_must_fail git repo info --keys --format=table 2>actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git repo info --keys aborts when requesting keys' '
+	echo "fatal: --keys cannot be used with a <key> or --all" >expect &&
+	test_must_fail git repo info --keys --all 2>actual_all &&
+	test_must_fail git repo info --keys some.key 2>actual_key &&
+	test_cmp expect actual_all &&
+	test_cmp expect actual_key
+'
+
+test_expect_success 'git repo info --keys uses lines as its default output format' '
+	git repo info --keys --format=lines >expect &&
+	git repo info --keys >actual &&
+	test_cmp expect actual
+'
+
 test_done