push: allow pushing new branches with --force-with-lease

If there is no upstream information for a branch, it is likely that it
is newly created and can safely be pushed under the normal fast-forward
rules.  Relax the --force-with-lease check so that we do not reject
these branches immediately but rather attempt to push them as new
branches, using the null SHA-1 as the expected value.

In fact, it is already possible to push new branches using the explicit
--force-with-lease=<branch>:<expect> syntax, so all we do here is make
this behaviour the default if no explicit "expect" value is specified.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -1554,8 +1554,7 @@ void set_ref_status_for_push(struct ref *remote_refs, int send_mirror,
 		 * branch.
 		 */
 		if (ref->expect_old_sha1) {
-			if (ref->expect_old_no_trackback ||
-			    oidcmp(&ref->old_oid, &ref->old_oid_expect))
+			if (oidcmp(&ref->old_oid, &ref->old_oid_expect))
 				reject_reason = REF_STATUS_REJECT_STALE;
 			else
 				/* If the ref isn't stale then force the update. */
@@ -2355,7 +2354,7 @@ static void apply_cas(struct push_cas_option *cas,
 		if (!entry->use_tracking)
 			hashcpy(ref->old_oid_expect.hash, cas->entry[i].expect);
 		else if (remote_tracking(remote, ref->name, &ref->old_oid_expect))
-			ref->expect_old_no_trackback = 1;
+			oidclr(&ref->old_oid_expect);
 		return;
 	}
 
@@ -2365,7 +2364,7 @@ static void apply_cas(struct push_cas_option *cas,
 
 	ref->expect_old_sha1 = 1;
 	if (remote_tracking(remote, ref->name, &ref->old_oid_expect))
-		ref->expect_old_no_trackback = 1;
+		oidclr(&ref->old_oid_expect);
 }
 
 void apply_push_cas(struct push_cas_option *cas,

remote.h

@@ -87,7 +87,6 @@ struct ref {
 		force:1,
 		forced_update:1,
 		expect_old_sha1:1,
-		expect_old_no_trackback:1,
 		deletion:1,
 		matched:1;
 

t/t5533-push-cas.sh

@@ -191,6 +191,18 @@ test_expect_success 'cover everything with default force-with-lease (allowed)' '
 	test_cmp expect actual
 '
 
+test_expect_success 'new branch covered by force-with-lease' '
+	setup_srcdst_basic &&
+	(
+		cd dst &&
+		git branch branch master &&
+		git push --force-with-lease=branch origin branch
+	) &&
+	git ls-remote dst refs/heads/branch >expect &&
+	git ls-remote src refs/heads/branch >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'new branch covered by force-with-lease (explicit)' '
 	setup_srcdst_basic &&
 	(