Issue #173: Ambiguity during Arrow instance resolution for ZIO and ZM…

…anaged (#174)

* fixed Ambiguity during Arrow instance resolution for ZIO and ZManaged

* fixing 'parameter is never used' compiler error on 2.12

* moving getArrow method and invocations to summoningInstancesTest

interop-cats/shared/src/main/scala/zio/interop/cats.scala

@@ -115,12 +115,6 @@ abstract class CatsInstances extends CatsInstances1 {
   implicit final def rioArrowInstance: ArrowChoice[RIO] =
     zioArrowInstance0.asInstanceOf[ArrowChoice[RIO]]
 
-  implicit final def urioArrowInstance: ArrowChoice[URIO] =
-    zioArrowInstance0.asInstanceOf[ArrowChoice[URIO]]
-
-  implicit final def zioArrowInstance[E]: ArrowChoice[ZIO[*, E, *]] =
-    zioArrowInstance0.asInstanceOf[ArrowChoice[ZIO[*, E, *]]]
-
   implicit final def contravariantInstance[E, A]: Contravariant[ZIO[*, E, A]] =
     contravariantInstance0.asInstanceOf[Contravariant[ZIO[*, E, A]]]
 
@@ -131,6 +125,9 @@ abstract class CatsInstances extends CatsInstances1 {
 
 sealed abstract class CatsInstances1 extends CatsInstances2 {
 
+  implicit final def urioArrowInstance: ArrowChoice[URIO] =
+    zioArrowInstance0.asInstanceOf[ArrowChoice[URIO]]
+
   implicit final def parallelInstance[R, E]: Parallel.Aux[ZIO[R, E, *], ParIO[R, E, *]] =
     parallelInstance0.asInstanceOf[Parallel.Aux[ZIO[R, E, *], ParIO[R, E, *]]]
 
@@ -148,6 +145,11 @@ sealed abstract class CatsInstances1 extends CatsInstances2 {
 }
 
 sealed abstract class CatsInstances2 {
+  protected[this] val zioArrowInstance0: ArrowChoice[ZIO[*, Any, *]] = new CatsArrow
+
+  implicit final def zioArrowInstance[E]: ArrowChoice[ZIO[*, E, *]] =
+    zioArrowInstance0.asInstanceOf[ArrowChoice[ZIO[*, E, *]]]
+
   implicit final def monadErrorInstance[R, E]: MonadError[ZIO[R, E, *], E] =
     monadErrorInstance0.asInstanceOf[MonadError[ZIO[R, E, *], E]]
 

interop-cats/shared/src/main/scala/zio/interop/catszmanaged.scala

@@ -120,11 +120,11 @@ trait CatsZManagedInstances extends CatsZManagedInstances1 {
       override def combine(x: ZManaged[R, E, A], y: ZManaged[R, E, A]): ZManaged[R, E, A] = x.zipWith(y)(ev.combine)
     }
 
-  implicit def arrowChoiceZManagedInstances[E]: ArrowChoice[ZManaged[*, E, *]] =
-    CatsZManagedArrowChoice.asInstanceOf[ArrowChoice[ZManaged[*, E, *]]]
+  implicit def arrowChoiceRManagedInstances[E]: ArrowChoice[RManaged] =
+    CatsZManagedArrowChoice.asInstanceOf[ArrowChoice[RManaged]]
 }
 
-sealed trait CatsZManagedInstances1 {
+sealed trait CatsZManagedInstances1 extends CatsZManagedInstances2 {
 
   implicit def monadZManagedInstances[R, E]: Monad[ZManaged[R, E, ?]] = new CatsZManagedMonad
 
@@ -138,6 +138,13 @@ sealed trait CatsZManagedInstances1 {
       fab.mapError(f).map(g)
   }
 
+  implicit def arrowChoiceURManagedInstances[E]: ArrowChoice[URManaged] =
+    CatsZManagedArrowChoice.asInstanceOf[ArrowChoice[URManaged]]
+}
+
+sealed trait CatsZManagedInstances2 {
+  implicit def arrowChoiceZManagedInstances[E]: ArrowChoice[ZManaged[*, E, *]] =
+    CatsZManagedArrowChoice.asInstanceOf[ArrowChoice[ZManaged[*, E, *]]]
 }
 
 private class CatsZManagedMonad[R, E] extends Monad[ZManaged[R, E, ?]] {

interop-cats/shared/src/test/scala/zio/interop/catzSpec.scala

@@ -1,5 +1,6 @@
 package zio.interop
 
+import cats.arrow.ArrowChoice
 import cats.effect.concurrent.Deferred
 import cats.effect.laws.discipline.arbitrary._
 import cats.effect.laws.discipline.{ ConcurrentEffectTests, ConcurrentTests, EffectTests, SyncTests }
@@ -80,6 +81,11 @@ class catzSpec extends catzSpecZIOBase {
 
     def concurrentEffect[R: Runtime] = ConcurrentEffect[RIO[R, *]]
     def effect[R: Runtime]           = Effect[RIO[R, *]]
+
+    // related to issue #173
+    def getArrow[F[-_, +_, +_], R, E, A](f: F[R, E, A])(implicit a: ArrowChoice[F[*, E, *]]): Any = (a, f)
+    getArrow(ZIO.environment[Int])
+    getArrow(ZManaged.environment[Int])
   }
 
   object summoningRuntimeInstancesTest {