Rebased. Ping @davidpdrsn can you review this?

CI fails because this change introduces unsafe code into a module that uses forbid(unsafe). I'd prefer to revert that part of the change (i.e. continue using pin-project-lite) so that we can avoid unsafe code in this crate.

pin-project-lite is almost definitely going to be in your dependency tree if you're using tokio.

I believe the issue is that moving Either to pin-project-lite is a breaking change.

I believe the issue is that moving Either to pin-project-lite is a breaking change.

That's a little surprising to me. Does pin-project-lite change the API surface when compared to pin-project? Howso?

If we can't use lite, I'd still prefer continuing use of pin-project if the alternative is adding unsafe code to tower -- it just expands the audit surface area. We're due for a breaking change sometime soon, I think, anyway. So we should get an issue to switch to use lite then if we really can't change now.

The issue with using pin-project-lite for Either is that it doesn't support tuple structs or tuple variants in enums. I don't think you would want to change ``Either::A(A)toEither::A { inner: A }`, right? In that case, the only options are to keep the `pin-project` dependency or accept the tiny bit of unsafe code. IMHO, the latter is better.

I'll separate that change from this PR though given that the other changes seem less controversial.

@jplatte That makes sense. Thanks for splitting out the change. We'll continue the conversation in #629