I frequently create "Marker Interfaces" for app specific pipelines that are simply interface MyPipeline extends MiddlewarePipeInterface {} and then refer to these in config/factories, but of course you don't actually get an implementation of these interfaces with this approach. My question is, would it be better to make MiddlewarePipe non-final in stratigility and instead make all of its public methods individually final? This way, I can safely extend MiddlewarePipe in an empty class to return an actual implementation of the correct type??

I would prefer having the whole pipeline retrievable via MiddlewarePipeInterface rather than ApplicationPipeline.

So I'd be open to add another service to reference MiddlewarePipeInterface instead.
One thing which we have to keep in mind is that when using laminas-servicemanager, we can not simply switch ApplicationPipeline to be an alias while adding the existing factory for MiddlewarePipeInterface. The reason is, that delegators can only be registered for services and thus existing delegators pointing to the fictional ApplicationPipeline service won't be applied anymore.

In order to these changes, the following needs to be done to this PR:

1. add alias MiddlewarePipeInterface pointing to ApplicationPipeline service
2. change ApplicationFactory to retrieve MiddlewarePipeInterface instead of ApplicationPipeline
3. Directly add @deprecated to the ApplicationPipeline to mark it deprecated so we can remove it in 4.0.0

In v4.0.0 we can drop all ApplicationPipeline references, change the ApplicationPipelineFactory to return the MiddlewarePipe again (as done before this patch) and thats it. Should be a smooth migration path as we would register the MiddlewarePipeInterface as a service instead of an alias and thus, all existing delegators which were registered in upstream projects targeting the fictive ApplicationPipeline service could be retargeted to the MiddlewarePipeInterface instead.

WDYT?

Sorry if I'm adding noise here. I think I misunderstood the ultimate goal of getting rid of ApplicationPipeline - In my previous comment I was referring to re-usable pipelines I'm in the habit of creating which I thought shared a similar mechanism for factory creation and could thus also benefit from better SA and a "best practice" way of writing these… I'll shut up now 😂

Whoops, psalm-baseline.xml needs some rebasing, sorry :(

I don't get why this is needed. What is the use case for this?

I don't get why this is needed. What is the use case for this?

The use-case is, that we get rid of magic services which do not represent actual classes but in-fact do provide a service via the container. Using FQCN are way more helpful than using random strings.

Given the fact, that some1 might want to decorate the application pipeline (whyever), one has to create a delegator for that non-FQCN (but namespaced, why the heck is it namespaced when its not an actual class anyways?) service name and then still needs to search in the source code what kind of service is actually returned.

Maybe this makes it clear:

We already use it as FQCN but it is not a class which does exist. Therefore, thats not really helpful when it comes to IDE autocompletion and stuff.

And this:

Changing service names in minors always leads to delegator registration issues.

Project config 3.10.X:

$config = [
    'dependencies' => [
       'delegators' => [
           'Mezzio\ApplicationPipeline' => [
                static function (ContainerInterface $container, string $requestedName, callable $pipelineFactory) {
                       $pipeline = $pipelineFactory();
                       $pipeline->pipe(MyMiddleware::class);
                       return $pipeline;
                } 
           ],
       ],
    ],
];

Project config 3.11.X:

$config = [
    'dependencies' => [
       'delegators' => [
           'Laminas\Stratigility\MiddlewarePipeInterface' => [
                static function (ContainerInterface $container, string $requestedName, callable $pipelineFactory) {
                       $pipeline = $pipelineFactory();
                       $pipeline->pipe(MyMiddleware::class);
                       return $pipeline;
                } 
           ],
       ],
    ],
];

Thus said, this would introduce a massive BC break to applications (from what I can see).
If we want to do that, just let me know and I'll change my PR regarding this.