check-ref-format --branch: give Porcelain a way to grok branch shorthand

The command may not be the best place to add this new feature, but

    $ git check-ref-format --branch "@{-1}"

allows Porcelains to figure out what branch you were on before the last
branch switching.

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

1 files changed, 10 insertions, 0 deletions

diff --git a/builtin-check-ref-format.c b/builtin-check-ref-format.c
index 701de439ae..39db6cbe47 100644
--- a/builtin-check-ref-format.c
+++ b/builtin-check-ref-format.c
@@ -5,9 +5,19 @@
 #include "cache.h"
 #include "refs.h"
 #include "builtin.h"
+#include "strbuf.h"
 
 int cmd_check_ref_format(int argc, const char **argv, const char *prefix)
 {
+	if (argc == 3 && !strcmp(argv[1], "--branch")) {
+		struct strbuf sb = STRBUF_INIT;
+		strbuf_branchname(&sb, argv[2]);
+		strbuf_splice(&sb, 0, 0, "refs/heads/", 11);
+		if (check_ref_format(sb.buf))
+			die("'%s' is not a valid branch name", argv[2]);
+		printf("%s\n", sb.buf + 11);
+		exit(0);
+	}
 	if (argc != 2)
 		usage("git check-ref-format refname");
 	return !!check_ref_format(argv[1]);