Add option to git-commit to allow empty log messages

Change git-commit(1) to accept the --allow-empty-message option
to allow a commit with an empty message.  This is analogous to the
existing --allow-empty option which allows a commit that records
no changes.  As these are mainly for interoperating with foreign SCM
systems, and are not meant for normal use, ensure that "git commit -h"
does not talk about them.
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-commit.txt

@@ -10,7 +10,7 @@ SYNOPSIS
 [verse]
 'git commit' [-a | --interactive] [-s] [-v] [-u<mode>] [--amend] [--dry-run]
 	   [(-c | -C) <commit>] [-F <file> | -m <msg>] [--reset-author]
-	   [--allow-empty] [--no-verify] [-e] [--author=<author>]
+	   [--allow-empty] [--allow-empty-message] [--no-verify] [-e] [--author=<author>]
 	   [--date=<date>] [--cleanup=<mode>] [--status | --no-status] [--]
 	   [[-i | -o ]<file>...]
 
@@ -131,6 +131,12 @@ OPTIONS
 	from making such a commit.  This option bypasses the safety, and
 	is primarily for use by foreign scm interface scripts.
 
+--allow-empty-message::
+       Like --allow-empty this command is primarily for use by foreign
+       scm interface scripts. It allows you to create a commit with an
+       empty commit message without using plumbing commands like
+       linkgit:git-commit-tree[1].
+
 --cleanup=<mode>::
 	This option sets how the commit message is cleaned up.
 	The  '<mode>' can be one of 'verbatim', 'whitespace', 'strip',

builtin/commit.c

@@ -66,7 +66,7 @@ static char *edit_message, *use_message;
 static char *author_name, *author_email, *author_date;
 static int all, edit_flag, also, interactive, only, amend, signoff;
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
-static int no_post_rewrite;
+static int no_post_rewrite, allow_empty_message;
 static char *untracked_files_arg, *force_date;
 /*
  * The default commit message cleanup mode will remove the lines
@@ -140,9 +140,15 @@ static struct option builtin_commit_options[] = {
 	OPT_BOOLEAN(0, "amend", &amend, "amend previous commit"),
 	OPT_BOOLEAN(0, "no-post-rewrite", &no_post_rewrite, "bypass post-rewrite hook"),
 	{ OPTION_STRING, 'u', "untracked-files", &untracked_files_arg, "mode", "show untracked files, optional modes: all, normal, no. (Default: all)", PARSE_OPT_OPTARG, NULL, (intptr_t)"all" },
-	OPT_BOOLEAN(0, "allow-empty", &allow_empty, "ok to record an empty change"),
 	/* end commit contents options */
 
+	{ OPTION_BOOLEAN, 0, "allow-empty", &allow_empty, NULL,
+	  "ok to record an empty change",
+	  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN },
+	{ OPTION_BOOLEAN, 0, "allow-empty-message", &allow_empty_message, NULL,
+	  "ok to record a change with an empty message",
+	  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN },
+
 	OPT_END()
 };
 
@@ -1293,7 +1299,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 
 	if (cleanup_mode != CLEANUP_NONE)
 		stripspace(&sb, cleanup_mode == CLEANUP_ALL);
-	if (message_is_empty(&sb)) {
+	if (message_is_empty(&sb) && !allow_empty_message) {
 		rollback_index_files();
 		fprintf(stderr, "Aborting commit due to empty commit message.\n");
 		exit(1);

t/t7500-commit.sh

@@ -193,4 +193,26 @@ test_expect_success 'commit -F overrides -t' '
 	commit_msg_is "-F log"
 '
 
+test_expect_success 'Commit without message is allowed with --allow-empty-message' '
+	echo "more content" >>foo &&
+	git add foo &&
+	>empty &&
+	git commit --allow-empty-message <empty &&
+	commit_msg_is ""
+'
+
+test_expect_success 'Commit without message is no-no without --allow-empty-message' '
+	echo "more content" >>foo &&
+	git add foo &&
+	>empty &&
+	test_must_fail git commit <empty
+'
+
+test_expect_success 'Commit a message with --allow-empty-message' '
+	echo "even more content" >>foo &&
+	git add foo &&
+	git commit --allow-empty-message -m"hello there" &&
+	commit_msg_is "hello there"
+'
+
 test_done