CSGen, SILGen: Fix delegations to Optional initializers

[AnthonyLatsis]

Resolves #57012 and more.

There remains a family of malfunctioning edge cases that I'm not sure what to make of. Specifically, when the constructed Optional value is force-unwrapped:

extension Optional {
  init(nonFailable: Void) { ... }
  init?(failable: Void) { ... }

  init(delegation1: Void) {
    self.init(nonFailable: ())! // this
  }

   init(delegation2: Void) {
    self.init(failable: ())!! // or this
  }
}

extension Optional where Wrapped == Optional<Bool> {
  init(delegation3: Void) {
    self.init(nonFailable: ())!! // or this
  }
}

I guess we should either deal with them using optional injections or ban them.

[AnthonyLatsis]

@swift-ci please smoke test macOS

[AnthonyLatsis]

@swift-ci please test source compatibility

[AnthonyLatsis]

@jckarter ping

[jckarter]

I think we should reject those other cases involving Optional that unwrap into the constructed value itself. The ! as part of a self.init(...)! is really only intended to let us delegate from a non-failable to a failable initializer of the same type. It shouldn't be possible to force-unwrap into the constructed value itself in the case where self is Optional.

[jckarter]

@swift-ci Please test

[AnthonyLatsis]

Thanks! Will put the addition of a tailored diagnostic for these force-unwraps on my radar.

[AnthonyLatsis]

@jckarter Could this (or maybe just the parts that resolve #57012) be nominated for inclusion in the release at this point?