Producer(auto_declare=True).publish() semantics

[povilasb]

The problem

Currently Producer with auto_declare set may have some unexpected semantics, at least to me :)

Here's a very basic example that most people would have a good sense of what's going to happen:

Producer(auto_declare=True).publish(b"message")

It will make sure the default exchange is declared before sending the message to.

However, consider such code:

Producer(auto_declare=True).publish(b"message", exchange="tasks")

If not reading the .publish() docs one could misinterpret the outcome

            exchange (kombu.entity.Exchange, str): Override the exchange.
                Note that this exchange must have been declared.

So now Producer will still try to declare the default exchange but publish to the "tasks" exchange:

        if self.auto_declare and self.exchange.name:
            if self.exchange not in declare:
                # XXX declare should be a Set.
                declare.append(self.exchange)

Potential change

What if auto_declare would try to declare the specified exchange instead?

1. default one if .publish() has no exchange specified
2. the one specified by .publish() otherwise

The same way the exchange name is already resolved before publishing:

        exchange_name, properties['delivery_mode'] = self._delivery_details(
            exchange or self.exchange, delivery_mode,
        )