Mark ServiceEntityRepository as lazy

[nicolas-grekas]

Replaces #1599
Fixes symfony/symfony#48666
See symfony/symfony#48666 (comment) for details.

[nicolas-grekas]

I just realized that lazy services are not compatible with final classes, so this might break some apps that aggressively make their repositories final.
That could be a reason to prefer #1599 instead.
Any opinion about the best way forward?

[ostrolucky]

Was that working before?

[nicolas-grekas]

Not really: the creation of the circular graph required double instantiations. This was mostly unnoticed but could still lead to strange situations where two different objects could be created (and passed to dependents) for the same service.

[ostrolucky]

Can we have a test for this?

[ostrolucky]

That sounds to me like proxying final repositories before was working before, but it could result in different instances. Did I get it right? If this issue wasn't a downside of #1599, what was a downside of that solution?

[nicolas-grekas]

Proxying final classes works only when there is an interface to rely on. That's not the case for repositories so this never worked.
The downside of #1599 is the dependency on the trait, but I suppose that's a lesser downside than forbidding final classes (I didn't spot this before opening this one.)
I'm reopening #1599

[ostrolucky]

Ok let's go with #1599