Tests covering those 2 attributes must be updated to be marked as @group legacy (and we need to ensure that tests covering those deprecated attributes are not used to also cover other parts that should remain tested after their removal, to avoid loosing coverage, splitting such tests in a legacy test and a non-legacy one instead)

Should this be more general... i fear this could feel a bit of a half seated DX too, with

return function (ContainerConfigurator $container): void {

    $services->set(Two::class)
        ->tag('app.handler', ['key' => 'handler_two']);

    $services->set(App\HandlerCollection::class)
        ->args([
            // 2nd argument is the index attribute name
            tagged_iterator('app.handler', 'key'),
        ])
    ;
};

Versus

class HandlerCollection
{
    public function __construct(
        #[AutowireIterator('app.handler', indexAttribute: 'key')]
        iterable $handlers
    ) {
    }
}

// ... 

#[AsTaggedItem(index: 'handler_one', priority: 10)]
class One
{
    // ...
}

You mean tagged_iterator is closer to #[TaggedIterator] than #[AutowireIterator].

But #[AutowireIterator] is part of the #[Autowire] attribute.

In terms of DX, we currently have 2 attributes that does the exact same thing.

I totally understand your motive here :)

What i feel is a lack of consistency / predictability here, that could be difficult to explain / document / etc.

So maybe we could rename AsTaggedItem too (as it's only used for tagged locator / iterator) ?

AutowiredItem ?

The name AsAutowiredItem would be misleading, because AsTaggedItem is unrelated to autowiring. It is autoconfiguration that applies the tag on the item with those properties, not autowiring. And this As* naming convention is the one followed by autoconfiguration attributes.

Thank you @GromNaN.