git-commit --allow-empty

It does not usually make sense to record a commit that has the exact
same tree as its sole parent commit and that is why git-commit prevents
you from making such a mistake, but when data from foreign scm is
involved, it is a different story.  We are equipped to represent such an
(perhaps insane, perhaps by mistake, or perhaps done on purpose) empty
change, and it is better to represent it bypassing the safety valve for
native use.

This is primarily for use by foreign scm interface scripts.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-commit.c

@@ -46,7 +46,7 @@ static enum {
 static char *logfile, *force_author, *template_file;
 static char *edit_message, *use_message;
 static int all, edit_flag, also, interactive, only, amend, signoff;
-static int quiet, verbose, untracked_files, no_verify;
+static int quiet, verbose, untracked_files, no_verify, allow_empty;
 
 static int no_edit, initial_commit, in_merge;
 const char *only_include_assumed;
@@ -87,6 +87,7 @@ static struct option builtin_commit_options[] = {
 	OPT_BOOLEAN('n', "no-verify", &no_verify, "bypass pre-commit hook"),
 	OPT_BOOLEAN(0, "amend", &amend, "amend previous commit"),
 	OPT_BOOLEAN(0, "untracked-files", &untracked_files, "show all untracked files"),
+	OPT_BOOLEAN(0, "allow-empty", &allow_empty, "ok to record an empty change"),
 
 	OPT_END()
 };
@@ -710,7 +711,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 
 	if (!prepare_log_message(index_file, prefix) && !in_merge &&
-	    !(amend && is_a_merge(head_sha1))) {
+	    !allow_empty && !(amend && is_a_merge(head_sha1))) {
 		run_status(stdout, index_file, prefix);
 		rollback_index_files();
 		unlink(commit_editmsg);