receive: denyCurrentBranch=updateinstead should not blindly update

The handling of receive.denyCurrentBranch=updateInstead was added to
a switch statement that handles other values of the variable, but
all the other case arms only checked a condition to reject the
attempted push, or let later logic in the same function to still
intervene, so that a push that does not fast-forward (which is
checked after the switch statement in question) is still rejected.

But the handling of updateInstead incorrectly took immediate effect,
without giving other checks a chance to intervene.

Instead of calling update_worktree() that causes the side effect
immediately, just note the fact that we will need to call the
function later, and first give other checks a chance to reject the
request.  After the update-hook gets a chance to reject the push
(which happens as the last step in a series of checks), call
update_worktree() when we earlier detected the need to.

Reported-by: Rajesh Madamanchi
Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

builtin/receive-pack.c

@@ -1037,6 +1037,7 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 	const char *ret;
 	struct object_id *old_oid = &cmd->old_oid;
 	struct object_id *new_oid = &cmd->new_oid;
+	int do_update_worktree = 0;
 
 	/* only refs/... are allowed */
 	if (!starts_with(name, "refs/") || check_refname_format(name + 5, 0)) {
@@ -1062,9 +1063,8 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 				refuse_unconfigured_deny();
 			return "branch is currently checked out";
 		case DENY_UPDATE_INSTEAD:
-			ret = update_worktree(new_oid->hash);
-			if (ret)
-				return ret;
+			/* pass -- let other checks intervene first */
+			do_update_worktree = 1;
 			break;
 		}
 	}
@@ -1129,6 +1129,12 @@ static const char *update(struct command *cmd, struct shallow_info *si)
 		return "hook declined";
 	}
 
+	if (do_update_worktree) {
+		ret = update_worktree(new_oid->hash);
+		if (ret)
+			return ret;
+	}
+
 	if (is_null_oid(new_oid)) {
 		struct strbuf err = STRBUF_INIT;
 		if (!parse_object(old_oid)) {

t/t5516-fetch-push.sh

@@ -1527,7 +1527,13 @@ test_expect_success 'receive.denyCurrentBranch = updateInstead' '
 		test $(git -C .. rev-parse master) = $(git rev-parse HEAD) &&
 		git diff --quiet &&
 		git diff --cached --quiet
-	)
+	) &&
+
+	# (6) updateInstead intervened by fast-forward check
+	test_must_fail git push void master^:master &&
+	test $(git -C void rev-parse HEAD) = $(git rev-parse master) &&
+	git -C void diff --quiet &&
+	git -C void diff --cached --quiet
 '
 
 test_expect_success 'updateInstead with push-to-checkout hook' '