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Deprecate shadowed sequenceVoid/sequence_/foldK in Foldable.Ops #4825

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Deprecate shadowed sequenceVoid/sequence_/foldK in Foldable.Ops #4825

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15 changes: 12 additions & 3 deletions core/src/main/scala/cats/Foldable.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1073,13 +1073,22 @@ object Foldable {
typeClassInstance.traverseVoid[G, A, B](self)(f)(G)
def traverse_[G[_], B](f: A => G[B])(implicit G: Applicative[G]): G[Unit] =
traverseVoid[G, B](f)
// TODO: looks like these two methods below duplicate the same named methods from `NestedFoldableOps`.
// Moreover, the other two methods take precedence, thereby these two are not in use whatsoever.
// Perhaps it makes sense to deprecate one pair of them either here or there.
@deprecated(
"Use catsSyntaxNestedFoldable (via cats.syntax.all._) to call sequenceVoid on F[G[A]]",
"2.13.0"
)
def sequenceVoid[G[_], B](implicit ev$1: A <:< G[B], ev$2: Applicative[G]): G[Unit] =
typeClassInstance.sequenceVoid[G, B](self.asInstanceOf[F[G[B]]])
@deprecated(
"Use catsSyntaxNestedFoldable (via cats.syntax.all._) to call sequence_ on F[G[A]]",
Comment on lines +1077 to +1083
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Copilot AI Feb 20, 2026

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The deprecation message suggests switching to catsSyntaxNestedFoldable/cats.syntax.all._, but these deprecated methods are selected specifically when the receiver is typed as F[A] with only an A <:< G[B] evidence (i.e., not an F[G[B]]), where NestedFoldableOps will not apply. Consider updating the message to a replacement that compiles in that scenario (e.g., using traverseVoid(ev$1) / traverse_ for sequencing).

Suggested change
"Use catsSyntaxNestedFoldable (via cats.syntax.all._) to call sequenceVoid on F[G[A]]",
"2.13.0"
)
def sequenceVoid[G[_], B](implicit ev$1: A <:< G[B], ev$2: Applicative[G]): G[Unit] =
typeClassInstance.sequenceVoid[G, B](self.asInstanceOf[F[G[B]]])
@deprecated(
"Use catsSyntaxNestedFoldable (via cats.syntax.all._) to call sequence_ on F[G[A]]",
"Use traverseVoid(ev$1) or traverse_(ev$1) for sequencing when you have evidence A <:< G[B].",
"2.13.0"
)
def sequenceVoid[G[_], B](implicit ev$1: A <:< G[B], ev$2: Applicative[G]): G[Unit] =
typeClassInstance.sequenceVoid[G, B](self.asInstanceOf[F[G[B]]])
@deprecated(
"Use traverse_(ev$1) for sequencing when you have evidence A <:< G[B].",

Copilot uses AI. Check for mistakes.
"2.13.0"
)
def sequence_[G[_], B](implicit ev$1: A <:< G[B], ev$2: Applicative[G]): G[Unit] =
sequenceVoid[G, B]
Comment on lines +1082 to 1087
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Copilot AI Feb 20, 2026

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Same as sequenceVoid: the suggested migration in the deprecation message (catsSyntaxNestedFoldable) may not be applicable when this overload is chosen (receiver not typed as F[G[_]]). Consider pointing users to a replacement that works with the existing A <:< G[B] evidence (e.g., traverse_(ev$1) / traverseVoid(ev$1)).

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@deprecated(
"Use catsSyntaxNestedFoldable (via cats.syntax.all._) to call foldK on F[G[A]]",
"2.13.0"
)
def foldK[G[_], B](implicit ev$1: A <:< G[B], G: MonoidK[G]): G[B] =
typeClassInstance.foldK[G, B](self.asInstanceOf[F[G[B]]])(G)
Comment on lines +1088 to 1093
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Copilot AI Feb 20, 2026

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The deprecation message points users at catsSyntaxNestedFoldable, but this foldK overload is picked when the value is not statically F[G[B]] (only A <:< G[B]). A migration hint that works in that case would be more actionable (e.g., foldMap(ev$1)(G.algebra[B]) using the existing MonoidK[G]).

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def find(f: A => Boolean): Option[A] = typeClassInstance.find[A](self)(f)
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4 changes: 0 additions & 4 deletions core/src/main/scala/cats/syntax/foldable.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -47,8 +47,6 @@ private[syntax] trait FoldableSyntaxBinCompat1 {
}

final class NestedFoldableOps[F[_], G[_], A](private val fga: F[G[A]]) extends AnyVal {
// TODO: looks like these two methods below duplicate the same named methods from `Foldable.Ops`.
// Perhaps it makes sense to deprecate one pair of them either here or there.
def sequenceVoid(implicit F: Foldable[F], G: Applicative[G]): G[Unit] = F.sequenceVoid(fga)
def sequence_(implicit F: Foldable[F], G: Applicative[G]): G[Unit] = sequenceVoid

Expand All @@ -64,8 +62,6 @@ final class NestedFoldableOps[F[_], G[_], A](private val fga: F[G[A]]) extends A
* res0: Set[Int] = Set(1, 2, 3, 4)
* }}}
*/
// TODO: looks like this method below duplicate the same named one from `Foldable.Ops`.
// Perhaps it makes sense to deprecate one of them.
def foldK(implicit F: Foldable[F], G: MonoidK[G]): G[A] = F.foldK(fga)
}

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