backported #3103 Add traverseFilter instances for Queue (#3292)

core/src/main/scala/cats/instances/all.scala

@@ -69,5 +69,6 @@ trait AllInstancesBinCompat7
     with VectorInstancesBinCompat1
     with EitherInstancesBinCompat0
     with StreamInstancesBinCompat1
+    with QueueInstancesBinCompat0
     with TailRecInstances
     with SortedSetInstancesBinCompat2

core/src/main/scala/cats/instances/queue.scala

@@ -2,6 +2,7 @@ package cats
 package instances
 
 import cats.syntax.show._
+
 import scala.annotation.tailrec
 import scala.collection.immutable.Queue
 import scala.util.Try
@@ -153,3 +154,31 @@ trait QueueInstances extends cats.kernel.instances.QueueInstances {
         fa.iterator.map(_.show).mkString("Queue(", ", ", ")")
     }
 }
+
+private[instances] trait QueueInstancesBinCompat0 {
+  implicit val catsStdTraverseFilterForQueue: TraverseFilter[Queue] = new TraverseFilter[Queue] {
+    val traverse: Traverse[Queue] = cats.instances.queue.catsStdInstancesForQueue
+
+    override def mapFilter[A, B](fa: Queue[A])(f: (A) => Option[B]): Queue[B] =
+      fa.collect(Function.unlift(f))
+
+    override def filter[A](fa: Queue[A])(f: (A) => Boolean): Queue[A] = fa.filter(f)
+
+    override def collect[A, B](fa: Queue[A])(f: PartialFunction[A, B]): Queue[B] = fa.collect(f)
+
+    override def flattenOption[A](fa: Queue[Option[A]]): Queue[A] = fa.flatten
+
+    def traverseFilter[G[_], A, B](fa: Queue[A])(f: (A) => G[Option[B]])(implicit G: Applicative[G]): G[Queue[B]] =
+      fa.foldRight(Eval.now(G.pure(Queue.empty[B])))(
+          (x, xse) => G.map2Eval(f(x), xse)((i, o) => i.fold(o)(_ +: o))
+        )
+        .value
+
+    override def filterA[G[_], A](fa: Queue[A])(f: (A) => G[Boolean])(implicit G: Applicative[G]): G[Queue[A]] =
+      fa.foldRight(Eval.now(G.pure(Queue.empty[A])))(
+          (x, xse) => G.map2Eval(f(x), xse)((b, vec) => if (b) x +: vec else vec)
+        )
+        .value
+  }
+
+}

tests/src/test/scala/cats/tests/QueueSuite.scala

@@ -2,13 +2,13 @@ package cats
 package tests
 
 import scala.collection.immutable.Queue
-
 import cats.laws.discipline.{
   AlternativeTests,
   CoflatMapTests,
   MonadTests,
   SemigroupalTests,
   SerializableTests,
+  TraverseFilterTests,
   TraverseTests
 }
 
@@ -28,6 +28,9 @@ class QueueSuite extends CatsSuite {
   checkAll("Queue[Int] with Option", TraverseTests[Queue].traverse[Int, Int, Int, Set[Int], Option, Option])
   checkAll("Traverse[Queue]", SerializableTests.serializable(Traverse[Queue]))
 
+  checkAll("Queue[Int]", TraverseFilterTests[Queue].traverseFilter[Int, Int, Int])
+  checkAll("TraverseFilter[Queue]", SerializableTests.serializable(TraverseFilter[Queue]))
+
   test("show") {
     Queue(1, 2, 3).show should ===("Queue(1, 2, 3)")
     Queue.empty[Int].show should ===("Queue()")