Thanks for the detailed description.
I'd prefer not adding this, because it means more exceptions to the rules of autoconfiguration.
But I do understand why it might be needed :)

Before, let me challenge the proposal:

• What about not ignoring a serializer.normalizer tag with no name when another one exists with a name? that'd be something to deal with in the compiler pass
• Please expand on Monolog channels/handlers so that we can wonder about similar more specific rules?

@nicolas-grekas Hi. Yeah, I see your point about exceptions. I'm not sure how many cases like this there actually are.

What about not ignoring a serializer.normalizer tag with no name when another one exists with a name? that'd be something to deal with in the compiler pass

I'm assuming you meant ignore the one without a name. I agree, that would solve the serializer case. However, there might be other cases besides this and the Monolog one.

Please expand on Monolog channels/handlers so that we can wonder about similar more specific rules?

Here's a simple example:

#[AsMonologProcessor('my_channel')]
final class MyProcessor implements ProcessorInterface
{
    public function __invoke(LogRecord $record) {}
}

You'd expect this processor to be registered only for my_channel, but because ProcessorInterface is registered for autoconfiguration, the processor is added to all channels.

The workaround is the same, disable autoconfiguration and add an explicit tag.

services:
    App\MyProcessor:
        autoconfigure: false
        tags:
            - monolog.processor: { channel: 'my_channel' }

I'd like to see how my proposal fits before looking for a more generic solution, to lower the overall complexity of things...