Re: pg_basebackup: could not get transaction log end position from server: FATAL: could not open file "./pg_hba.conf~": Permission denied

That's pretty much what it does if you enable progress meter. I realize you don't necessarily want that one, but we could have a switch that still tells the server to measure the size, but not actually print the output? While it costs a bit of overhead to do that, that's certainly something that's a lot more safe than ignoring errors.