builtin/am: introduce write_state_*() helper functions

diff --git a/builtin/update-ref.c b/builtin/update-ref.c
index 3d79a46b036fa7bea29bbc0941442b5dd92f648c..6763cf1837db99442a7140fe5bb87a0b3a1248fd 100644 (file)
--- a/builtin/update-ref.c
+++ b/builtin/update-ref.c
@@ -408,14 +408,27 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
                        die("%s: not a valid SHA1", value);
        }
 
-       hashclr(oldsha1); /* all-zero hash in case oldval is the empty string */
-       if (oldval && *oldval && get_sha1(oldval, oldsha1))
-               die("%s: not a valid old SHA1", oldval);
+       if (oldval) {
+               if (!*oldval)
+                       /*
+                        * The empty string implies that the reference
+                        * must not already exist:
+                        */
+                       hashclr(oldsha1);
+               else if (get_sha1(oldval, oldsha1))
+                       die("%s: not a valid old SHA1", oldval);
+       }
 
        if (no_deref)
                flags = REF_NODEREF;
        if (delete)
-               return delete_ref(refname, oldval ? oldsha1 : NULL, flags);
+               /*
+                * For purposes of backwards compatibility, we treat
+                * NULL_SHA1 as "don't care" here:
+                */
+               return delete_ref(refname,
+                                 (oldval && !is_null_sha1(oldsha1)) ? oldsha1 : NULL,
+                                 flags);
        else
                return update_ref(msg, refname, sha1, oldval ? oldsha1 : NULL,
                                  flags, UPDATE_REFS_DIE_ON_ERR);