update-ref: -d flag and ref creation safety.

This adds -d flag to update-ref to allow safe deletion of ref.
Before deleting it, the command checks if the given <oldvalue>
still matches the value the caller thought the ref contained.

Similarly, it also accepts 0{40} or an empty string as <oldvalue>
to allow safe creation of a new ref.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index 6def15516..6e004505b 100644
--- a/cache.h
+++ b/cache.h
@@ -179,6 +179,7 @@ struct lock_file {
 extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
 extern int commit_lock_file(struct lock_file *);
 extern void rollback_lock_file(struct lock_file *);
+extern int delete_ref(const char *, unsigned char *sha1);
 
 /* Environment bits from configuration mechanism */
 extern int use_legacy_headers;