Duplicate detection of forwarded dependencies

[kubukoz]

Hi!

In 0.3.2, as I understand, this is an issue:

import zio.ZLayer
import zio.Has
import zio.magic._

class Demo {
  trait A
  trait B
  trait C

  val a: ZLayer[Any, Nothing, Has[A]] =
    ZLayer.succeed(new A {})

  val x: ZLayer[Has[A], Nothing, Has[B] with Has[A]] =
    ZLayer.wireSome[Has[A], Has[B] with Has[A]](ZLayer.succeed(new B {}))

  val y: ZLayer[Has[A], Nothing, Has[C]] =
    ZLayer.wire[Has[C]](ZLayer.succeed(new C {}))

  val bc: ZLayer[Any, Nothing, Has[B] with Has[C]] =
    ZLayer.wire[Has[B] with Has[C]](a, x, y)
}

The macro says:

  ZLayer Wiring Error  

❯ Demo.this.A is provided by multiple layers:
❯ — a
❯ — x

Which is true. However, A appears in both the input and output of the x layer, which zio-magic could probably always treat as "passing the same thing we got in the input" and allow.

If this change stays as it is, I'll need to do some extra work to migrate, which is fine, just wanted to make sure this was intended and not going to change :)

[kitlangton]

I'll fix this. Basically, I'll prune each layers inputs from its outputs, so it doesn't consider these "pass-through" layers as candidates—or worse, as circular dependencies.

[kubukoz]

Sounds great :) thanks for looking at this