I'm using the Symfony bundle. I start my consumer using bin/console enqueue/consume and sure enough it works just fine.

However if one of the consumed messages causes an exception, the consumer freezes without even writing anything to console or log - the exception is nowhere to be seen.

I used xdebug to find out what caused it and I believe the reason is that Symfony/Console runs into an infinite loop while trying to print the exception.

The reason why that happens is this code in your bundle:

It effectively creates a pair of exceptions where each has set the other one as the previous:

$e->getPrevious()->getPrevious() === $e // true

(or a longer chain of exceptions where the last one has the first one as previous - still effectively a cycle of exceptions)

I don't quite understand what is the idea behind this but obviously when an error handler tries to dump the exception chain this causes an infinite loop because ->getPrevious() never returns null.

Can you explain what the code in QueueConsumer::onProcessorException() is supposed to do? I'm quite sure this isn't intentional. When I remove the code I linked above, everything works as expected.