Extending a service from a DeferrableProvider

[GromNaN]

When a ServiceProvider implements the DeferrableProvider interface, it is registered only when one of the services declared in its provides() method is built.

class CoreServiceProvider extends ServiceProvider implements DeferrableProvider
{
    public function register()
    {
        $this->app->singleton(CoreInterface::class, function (Container $app) { ... });
    }

    public function provides()
    {
        return [CoreInterface::class];
    }
}

Problem

My issue is to extend one of this services in a DeferrableProvider provided by my package. If I add the service name in the "provides" list, it replaces the original CoreServiceProvider. So I can't extend it. I could only redefine it with $app->singleton().

class MyPackageServiceProvider extends ServiceProvider implements DeferrableProvider
{
    public function register()
    {
        $this->app->extends(CoreInterface::class, function (CoreInterface $instance, Container $app) { ... });
        // ERROR! The service "CoreInterface" is not instantiable because the CoreServiceProvider is not registered
    }

    public function provides()
    {
        return [CoreInterface::class];
    }
}

If the service name is not in the "provides" list, my provider is never registered.

class MyPackageServiceProvider extends ServiceProvider implements DeferrableProvider
{
    public function register()
    {
        $this->app->extends(CoreInterface::class, function (CoreInterface $instance, Container $app) { ... });
        // FAILED! This is never registered
    }

    public function provides()
    {
        return [];
    }
}

Partial solution

My current solution is to explicitly call the CoreServiceProvider from MyPackageServiceProvider. But this is not 100% safe as an other package could extend the same service. It would not be registered either.

class MyPackageServiceProvider extends ServiceProvider implements DeferrableProvider
{
    public function register()
    {
        // Explicitly register the parent provider
        $this->app->register(CoreServiceProvider::class);

        $this->app->extends(CoreInterface::class, function (CoreInterface $instance, Container $app) { ... });
        // SUCCESS!
    }

    public function provides()
    {
        return [CoreInterface::class];
    }
}

Actually implemented in mongodb/laravel-mongodb#3071

Proposition

All the service providers providing a service should be called. Instead of having a single provider per service name, it should be a list:

framework/src/Illuminate/Foundation/ProviderRepository.php

Line 149 in b18f333

$manifest['deferred'][$service] = $provider;

- $manifest['deferred'][$service] = $provider;
+ $manifest['deferred'][$service][] = $provider;

And all the associated providers would be registered when the service is built.