Re: synchronous_standby_names with '*'

I think if master has not slave's at this time then server must use "local"
mode. But if he has >=1 slave then he must wait until slave accept
transaction. And "synchronous_standby_names" select behaviour about how
master shoud select which slave must be synchronous or not. And when this
GUC is '*' master should use first in the list IMHO.
In docs you (developers) write

PostgreSQL does not provide the system software required to identify a
failure on the primary and notify the standby database server.

But I think you don't have provide software to identify *AND* standby
failure (only notification about this situation's) - and this master without
slave is this failure (slave don't started)