// This doesn't compile in either 2.12 or 2.13
val x1: Step4[InferenceUtil.P,Children.None,Unit,Unit,UpdateSnapshot.None                  ] = start
val x2: Step4[InferenceUtil.P,Children.None,Unit,Unit,UpdateSnapshot.Some[x1.SnapshotValue]] = x1.componentDidUpdate($ => Callback(testExpr($.snapshot).expect[Unit]))
val x3: Step4[InferenceUtil.P,Children.None,Unit,Unit,UpdateSnapshot.Some[x1.SnapshotValue]] = x2.componentDidUpdate($ => Callback(testExpr($.snapshot).expect[Unit]))
implicitly[x1.SnapshotValue =:= Unit]

// This compiles in both 2.12 and 2.13, we've just unalised y1.SnapshotValue to Unit
val y1: Step4[InferenceUtil.P,Children.None,Unit,Unit,UpdateSnapshot.None      ] = start
val y2: Step4[InferenceUtil.P,Children.None,Unit,Unit,UpdateSnapshot.Some[Unit]] = y1.componentDidUpdate($ => Callback(testExpr($.snapshot).expect[Unit]))
val y3: Step4[InferenceUtil.P,Children.None,Unit,Unit,UpdateSnapshot.Some[Unit]] = y2.componentDidUpdate($ => Callback(testExpr($.snapshot).expect[Unit]))
implicitly[y1.SnapshotValue =:= Unit]

// If we let type inference do its thing on the following block...
//   - on Scala 2.13.0 it infers the types in the first case above, and fails to compile
//   - on Scala 2.12.8 it infers the types in the second case above, and compiles
start
  .componentDidUpdate($ => Callback(testExpr($.snapshot).expect[Unit]))
  .componentDidUpdate($ => Callback(testExpr($.snapshot).expect[Unit]))