Merge pull request #3361 from travisbrown/fix/3360

Restrict attemptNarrow to subtypes of Throwable
typelevel · Mar 19, 2020 · 824a4b3 · 824a4b3
2 parents b03df99 + a32c7aa
commit 824a4b3
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Showing 3 changed files with 7 additions and 5 deletions.
diff --git a/core/src/main/scala/cats/ApplicativeError.scala b/core/src/main/scala/cats/ApplicativeError.scala
@@ -80,7 +80,7 @@ trait ApplicativeError[F[_], E] extends Applicative[F] {
   /**
    * Similar to [[attempt]], but it only handles errors of type `EE`.
    */
-  def attemptNarrow[EE, A](fa: F[A])(implicit tag: ClassTag[EE], ev: EE <:< E): F[Either[EE, A]] =
+  def attemptNarrow[EE <: Throwable, A](fa: F[A])(implicit tag: ClassTag[EE], ev: EE <:< E): F[Either[EE, A]] =
     recover(map(fa)(Right[EE, A](_): Either[EE, A])) { case e: EE => Left[EE, A](e) }
 
   /**

diff --git a/core/src/main/scala/cats/syntax/applicativeError.scala b/core/src/main/scala/cats/syntax/applicativeError.scala
@@ -51,7 +51,9 @@ final class ApplicativeErrorOps[F[_], E, A](private val fa: F[A]) extends AnyVal
   def attempt(implicit F: ApplicativeError[F, E]): F[Either[E, A]] =
     F.attempt(fa)
 
-  def attemptNarrow[EE](implicit F: ApplicativeError[F, E], tag: ClassTag[EE], ev: EE <:< E): F[Either[EE, A]] =
+  def attemptNarrow[EE <: Throwable](implicit F: ApplicativeError[F, E],
+                                     tag: ClassTag[EE],
+                                     ev: EE <:< E): F[Either[EE, A]] =
     F.attemptNarrow[EE, A](fa)
 
   def attemptT(implicit F: ApplicativeError[F, E]): EitherT[F, E, A] =

diff --git a/tests/src/test/scala/cats/tests/ApplicativeErrorSuite.scala b/tests/src/test/scala/cats/tests/ApplicativeErrorSuite.scala
@@ -29,7 +29,7 @@ class ApplicativeErrorSuite extends CatsSuite {
   }
 
   test("attemptNarrow[EE] syntax creates an F[Either[EE, A]]") {
-    trait Err
+    trait Err extends Throwable
     case class ErrA() extends Err
     case class ErrB() extends Err
 
@@ -44,7 +44,7 @@ class ApplicativeErrorSuite extends CatsSuite {
   }
 
   test("attemptNarrow works for parametrized types") {
-    trait T[A]
+    trait T[A] extends Throwable
     case object Str extends T[String]
     case class Num(i: Int) extends T[Int]
 
@@ -61,7 +61,7 @@ class ApplicativeErrorSuite extends CatsSuite {
     assertTypeError("e2.attemptNarrow[Num]")
 
     val e3: Either[List[T[String]], Unit] = List(Str).asLeft[Unit]
-    e3.attemptNarrow[List[Str.type]] should ===(e3.asRight[List[T[String]]])
+    assertTypeError("e3.attemptNarrow[List[Str.type]]")
     assertTypeError("e3.attemptNarrow[List[Num]]")
   }