Can't migrate from v0.7: StateT[EitherT, ...], ...] vs. EitherT[StateT, ...], ...] about cats-mtl HOT 1 OPEN

@marcinzh

Just traversing this repo and found your issue here. Intrigued me somehow so I checked it. While looking at your github I am pretty sure you know the fix, however let me post here my findings:

• If you change Raise to Handle your code will work. Handle extends Raise but it is somehow not being resolved here for the StateT (maybe it's a compiler bug?)
• so the patch is simple (?) and is about creating a Raise provider for StateT based on Handler.handleStateT function:

diff --git a/core/src/main/scala/cats/mtl/Raise.scala b/core/src/main/scala/cats/mtl/Raise.scala
index a29b70d..ea67cf9 100644
--- a/core/src/main/scala/cats/mtl/Raise.scala
+++ b/core/src/main/scala/cats/mtl/Raise.scala
@@ -124,6 +124,8 @@ private[mtl] trait RaiseInstances extends LowPriorityRaiseInstances {
       F: Monad[F]): Raise[IorT[F, E, *], E] =
     Handle.handleIorT[F, E]

+  implicit final def raiseStateT[F[_], E, S](implicit F0: Handle[F, E], M: Monad[F]): Raise[StateT[F, S, *], E] = Handle.handleStateT
+
 }

It works, however I haven't check if this interferes with other parts of this repository (laws etc.).

from cats-mtl.