Make old sha1 optional with git update-ref -d

Giving the old sha1 is already optional when changing a ref, and it's
quite handy when running update-ref manually. So make it optional for
deleting a ref too.

Signed-off-by: Karl Hasselström <kha@treskal.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-update-ref.txt

@@ -7,7 +7,7 @@ git-update-ref - Update the object name stored in a ref safely
 
 SYNOPSIS
 --------
-'git-update-ref' [-m <reason>] (-d <ref> <oldvalue> | [--no-deref] <ref> <newvalue> [<oldvalue>])
+'git-update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])
 
 DESCRIPTION
 -----------

builtin-update-ref.c

@@ -4,7 +4,7 @@
 #include "parse-options.h"
 
 static const char * const git_update_ref_usage[] = {
-	"git-update-ref [options] -d <refname> <oldval>",
+	"git-update-ref [options] -d <refname> [<oldval>]",
 	"git-update-ref [options]    <refname> <newval> [<oldval>]",
 	NULL
 };
@@ -28,7 +28,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		die("Refusing to perform update with empty message.");
 
 	if (delete) {
-		if (argc != 2)
+		if (argc < 1 || argc > 2)
 			usage_with_options(git_update_ref_usage, options);
 		refname = argv[0];
 		oldval = argv[1];
@@ -48,7 +48,7 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
 		die("%s: not a valid old SHA1", oldval);
 
 	if (delete)
-		return delete_ref(refname, oldsha1);
+		return delete_ref(refname, oldval ? oldsha1 : NULL);
 	else
 		return update_ref(msg, refname, sha1, oldval ? oldsha1 : NULL,
 				  no_deref ? REF_NODEREF : 0, DIE_ON_ERR);

t/t1400-update-ref.sh

@@ -42,6 +42,14 @@ test_expect_success "delete $m" '
 '
 rm -f .git/$m
 
+test_expect_success "delete $m without oldvalue verification" "
+	git update-ref $m $A &&
+	test $A = \$(cat .git/$m) &&
+	git update-ref -d $m &&
+	! test -f .git/$m
+"
+rm -f .git/$m
+
 test_expect_success \
 	"fail to create $n" \
 	"touch .git/$n_dir