Merge pull request #4576 from joroKr21/bugfix/eithert

Fix EitherT Bifunctor priority, add Bifoldable instance
typelevel · Mar 23, 2024 · 3d3f63a · 3d3f63a
2 parents 236b7fd + 04f7c28
commit 3d3f63a
Show file tree

Hide file tree

Showing 2 changed files with 27 additions and 9 deletions.
diff --git a/core/src/main/scala/cats/data/EitherT.scala b/core/src/main/scala/cats/data/EitherT.scala
@@ -965,10 +965,8 @@ abstract private[data] class EitherTInstances extends EitherTInstances1 {
   implicit def catsDataShowForEitherT[F[_], L, R](implicit sh: Show[F[Either[L, R]]]): Show[EitherT[F, L, R]] =
     Contravariant[Show].contramap(sh)(_.value)
 
-  implicit def catsDataBifunctorForEitherT[F[_]](implicit F: Functor[F]): Bifunctor[EitherT[F, *, *]] =
-    new EitherTBifunctor[F] {
-      val F0: Functor[F] = F
-    }
+  implicit def catsDataBitraverseForEitherT[F[_]](implicit F: Traverse[F]): Bitraverse[EitherT[F, *, *]] =
+    new EitherTBitraverse[F] { val F0 = F }
 
   implicit def catsDataTraverseForEitherT[F[_], L](implicit FF: Traverse[F]): Traverse[EitherT[F, L, *]] =
     new EitherTTraverse[F, L] with EitherTFunctor[F, L] {
@@ -1093,10 +1091,11 @@ abstract private[data] class EitherTInstances1 extends EitherTInstances2 {
       val F0: PartialOrder[F[Either[L, R]]] = F
     }
 
-  implicit def catsDataBitraverseForEitherT[F[_]](implicit F: Traverse[F]): Bitraverse[EitherT[F, *, *]] =
-    new EitherTBitraverse[F] with EitherTBifunctor[F] {
-      val F0: Traverse[F] = F
-    }
+  implicit def catsDataBifunctorForEitherT[F[_]](implicit F: Functor[F]): Bifunctor[EitherT[F, *, *]] =
+    new EitherTBifunctor[F] { val F0 = F }
+
+  implicit def catsDataBifoldableForEitherT[F[_]](implicit F: Foldable[F]): Bifoldable[EitherT[F, *, *]] =
+    new EitherTBifoldable[F] { val F0 = F }
 
   implicit def catsDataMonadErrorForEitherT[F[_], L](implicit F0: Monad[F]): MonadError[EitherT[F, L, *], L] =
     new EitherTMonadError[F, L] {

diff --git a/tests/shared/src/test/scala/cats/tests/EitherTSuite.scala b/tests/shared/src/test/scala/cats/tests/EitherTSuite.scala
@@ -38,6 +38,12 @@ class EitherTSuite extends CatsSuite {
   implicit val iso: Isomorphisms[EitherT[ListWrapper, String, *]] = Isomorphisms
     .invariant[EitherT[ListWrapper, String, *]](EitherT.catsDataFunctorForEitherT(ListWrapper.functor))
 
+  // Test instance summoning
+  def summon[F[_]: Traverse](): Unit = {
+    Bifunctor[EitherT[F, *, *]]
+    Bifoldable[EitherT[F, *, *]]
+  }
+
   checkAll("EitherT[Eval, String, *]", DeferTests[EitherT[Eval, String, *]].defer[Int])
 
   {
@@ -74,6 +80,20 @@ class EitherTSuite extends CatsSuite {
     )
   }
 
+  {
+    // if a Foldable for F is defined
+    implicit val F: Foldable[ListWrapper] = ListWrapper.foldable
+
+    checkAll("EitherT[ListWrapper, Int, *]", FoldableTests[EitherT[ListWrapper, Int, *]].foldable[Int, Int])
+    checkAll("Foldable[EitherT[ListWrapper, Int, *]]",
+             SerializableTests.serializable(Foldable[EitherT[ListWrapper, Int, *]])
+    )
+    checkAll("EitherT[ListWrapper, *, *]", BifoldableTests[EitherT[ListWrapper, *, *]].bifoldable[Int, Int, Int])
+    checkAll("Bifoldable[EitherT[ListWrapper, *, *]]",
+             SerializableTests.serializable(Bifoldable[EitherT[ListWrapper, *, *]])
+    )
+  }
+
   {
     // if a Traverse for F is defined
     implicit val F: Traverse[ListWrapper] = ListWrapper.traverse
@@ -90,7 +110,6 @@ class EitherTSuite extends CatsSuite {
     checkAll("Bitraverse[EitherT[ListWrapper, *, *]]",
              SerializableTests.serializable(Bitraverse[EitherT[ListWrapper, *, *]])
     )
-
   }
 
   {