chore: remove leftover Scala 2.12 idioms

discovery-aws-api-async/src/main/scala/org/apache/pekko/discovery/awsapi/ecs/AsyncEcsServiceDiscovery.scala

@@ -16,7 +16,6 @@ package org.apache.pekko.discovery.awsapi.ecs
 import java.net.InetAddress
 import java.util.concurrent.TimeoutException
 
-import scala.collection.immutable.Seq
 import scala.concurrent.duration._
 import scala.concurrent.{ ExecutionContext, Future }
 import scala.jdk.CollectionConverters._

discovery-aws-api-async/src/main/scala/org/apache/pekko/discovery/awsapi/ecs/AsyncEcsTaskSetDiscovery.scala

@@ -16,7 +16,6 @@ package org.apache.pekko.discovery.awsapi.ecs
 import java.net.InetAddress
 import java.util.concurrent.TimeoutException
 
-import scala.collection.immutable.Seq
 import scala.concurrent.duration._
 import scala.concurrent.{ ExecutionContext, Future }
 import scala.jdk.CollectionConverters._

discovery-aws-api/src/main/scala/org/apache/pekko/discovery/awsapi/ec2/Ec2TagBasedServiceDiscovery.scala

@@ -30,7 +30,6 @@ import pekko.pattern.after
 import java.net.InetAddress
 import java.util.concurrent.TimeoutException
 import scala.annotation.tailrec
-import scala.collection.immutable.Seq
 import scala.concurrent.duration.FiniteDuration
 import scala.concurrent.{ ExecutionContext, Future }
 import scala.jdk.CollectionConverters._

discovery-aws-api/src/main/scala/org/apache/pekko/discovery/awsapi/ecs/EcsServiceDiscovery.scala

@@ -31,7 +31,6 @@ import com.amazonaws.services.ecs.model.{ DescribeTasksRequest, DesiredStatus, L
 import com.amazonaws.services.ecs.{ AmazonECS, AmazonECSClientBuilder }
 
 import scala.annotation.tailrec
-import scala.collection.immutable.Seq
 import scala.concurrent.{ ExecutionContext, Future }
 import scala.concurrent.duration._
 import scala.jdk.CollectionConverters._

discovery-consul/src/main/scala/org/apache/pekko/discovery/consul/ConsulServiceDiscovery.scala

@@ -34,7 +34,6 @@ import java.security.cert.CertificateFactory
 import java.util
 import java.util.concurrent.TimeoutException
 import javax.net.ssl.{ SSLContext, TrustManagerFactory }
-import scala.collection.immutable.Seq
 import scala.concurrent.duration.FiniteDuration
 import scala.concurrent.{ ExecutionContext, Future, Promise }
 import scala.jdk.CollectionConverters._
@@ -107,7 +106,7 @@ class ConsulServiceDiscovery(system: ActorSystem) extends ServiceDiscovery {
         Future(extractResolvedTargetFromCatalogService(catalogService))(blockingEc)
       }
     } yield resolvedTargets
-    consulResult.map(targets => Resolved(name, scala.collection.immutable.Seq(targets: _*)))
+    consulResult.map(targets => Resolved(name, targets))
   }
 
   private def extractResolvedTargetFromCatalogService(catalogService: CatalogService) = {

discovery-kubernetes-api/src/main/scala/org/apache/pekko/discovery/kubernetes/KubernetesApiServiceDiscovery.scala

@@ -18,8 +18,6 @@ import java.nio.charset.StandardCharsets
 import java.util.concurrent.TimeoutException
 import java.nio.file.{ Files, Paths }
 
-import scala.collection.immutable
-import scala.collection.immutable.Seq
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
 import scala.concurrent.Promise
@@ -59,7 +57,7 @@ object KubernetesApiServiceDiscovery {
       podNamespace: String,
       podDomain: String,
       rawIp: Boolean,
-      containerName: Option[String]): immutable.Seq[ResolvedTarget] =
+      containerName: Option[String]): Seq[ResolvedTarget] =
     for {
       item <- podList.items
       if item.metadata.flatMap(_.deletionTimestamp).isEmpty
@@ -240,7 +238,7 @@ class KubernetesApiServiceDiscovery(settings: Settings)(
       val query = Uri.Query("labelSelector" -> labelSelector)
       val uri = Uri.from(scheme = "https", host = host, port = port).withPath(path).withQuery(query)
 
-      val authHeaders = immutable.Seq(Authorization(OAuth2BearerToken(token)))
+      val authHeaders = Seq(Authorization(OAuth2BearerToken(token)))
       val acceptEncodingHeader = HttpEncodings.getForKey(settings.httpRequestAcceptEncoding)
         .map(httpEncoding => AcceptEncoding.create(httpEncoding))
       HttpRequest(uri = uri, headers = authHeaders ++ acceptEncodingHeader)

discovery-kubernetes-api/src/main/scala/org/apache/pekko/discovery/kubernetes/PodList.scala

@@ -13,7 +13,6 @@
 
 package org.apache.pekko.discovery.kubernetes
 
-import scala.collection.immutable
 import org.apache.pekko.annotation.InternalApi
 
 /**
@@ -24,15 +23,15 @@ import org.apache.pekko.annotation.InternalApi
 
   final case class ContainerPort(name: Option[String], containerPort: Int)
 
-  final case class Container(name: String, ports: Option[immutable.Seq[ContainerPort]])
+  final case class Container(name: String, ports: Option[Seq[ContainerPort]])
 
-  final case class PodSpec(containers: immutable.Seq[Container])
+  final case class PodSpec(containers: Seq[Container])
 
   final case class ContainerStatus(name: String, state: Map[String, Unit])
 
   final case class PodStatus(
       podIP: Option[String],
-      containerStatuses: Option[immutable.Seq[ContainerStatus]],
+      containerStatuses: Option[Seq[ContainerStatus]],
       phase: Option[String])
 
   final case class Pod(spec: Option[PodSpec], status: Option[PodStatus], metadata: Option[Metadata])
@@ -41,4 +40,4 @@ import org.apache.pekko.annotation.InternalApi
 /**
  * INTERNAL API
  */
-@InternalApi private[kubernetes] final case class PodList(items: immutable.Seq[PodList.Pod])
+@InternalApi private[kubernetes] final case class PodList(items: Seq[PodList.Pod])

discovery-marathon-api/src/main/scala/org/apache/pekko/discovery/marathon/AppList.scala

@@ -13,8 +13,6 @@
 
 package org.apache.pekko.discovery.marathon
 
-import scala.collection.immutable.Seq
-
 object AppList {
   case class App(container: Option[Container], portDefinitions: Option[Seq[PortDefinition]], tasks: Option[Seq[Task]])
   case class Container(portMappings: Option[Seq[PortMapping]], docker: Option[Docker])

discovery-marathon-api/src/main/scala/org/apache/pekko/discovery/marathon/MarathonApiServiceDiscovery.scala

@@ -20,7 +20,6 @@ import pekko.http.scaladsl._
 import pekko.http.scaladsl.model._
 import pekko.http.scaladsl.unmarshalling.Unmarshal
 
-import scala.collection.immutable.Seq
 import scala.concurrent.Future
 import scala.concurrent.duration.FiniteDuration
 import scala.util.Try

lease-kubernetes-int-test/src/test/scala/org/apache/pekko/coordination/lease/kubernetes/LeaseContentionSpec.scala

@@ -11,7 +11,6 @@ package org.apache.pekko.coordination.lease.kubernetes
 
 import java.util.concurrent.Executors
 
-import scala.collection.immutable
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
 
@@ -76,7 +75,7 @@ class LeaseContentionSpec extends TestKit(ActorSystem("LeaseContentionSpec",
       val nrClients = 30
       implicit val ec: ExecutionContext = ExecutionContext.fromExecutor(Executors.newFixedThreadPool(nrClients)) // too many = HTTP request queue of pool fills up
       // could make this more contended with a countdown latch so they all start at the same time
-      val leases: immutable.Seq[(String, Boolean)] = Future.sequence((0 until nrClients).map(i => {
+      val leases: Seq[(String, Boolean)] = Future.sequence((0 until nrClients).map(i => {
         val clientName = s"client$i"
         val lease = underTest.getLease(lease1, KubernetesLease.configPath, clientName)
         Future {

lease-kubernetes/src/main/scala/org/apache/pekko/coordination/lease/kubernetes/internal/AbstractKubernetesApiImpl.scala

@@ -31,7 +31,6 @@ import pekko.util.ByteString
 
 import java.nio.file.{ Files, Paths }
 import javax.net.ssl.SSLContext
-import scala.collection.immutable
 import scala.concurrent.{ ExecutionContext, Future, Promise }
 import scala.util.control.NonFatal
 
@@ -69,7 +68,7 @@ import scala.util.control.NonFatal
     _.getOrElse(""))(ExecutionContext.parasitic)
   private def headers() = if (settings.secure) {
     apiToken().map { token =>
-      immutable.Seq(Authorization(OAuth2BearerToken(token)))
+      Seq(Authorization(OAuth2BearerToken(token)))
     }(ExecutionContext.parasitic)
   } else
     Future.successful(Nil)

management-cluster-bootstrap/src/main/scala/org/apache/pekko/management/cluster/bootstrap/internal/BootstrapCoordinator.scala

@@ -85,16 +85,16 @@ private[pekko] object BootstrapCoordinator {
       lookup: Lookup,
       fallbackPort: Int,
       filterOnFallbackPort: Boolean,
-      contactPoints: immutable.Seq[ResolvedTarget]): immutable.Iterable[ResolvedTarget] = {
+      contactPoints: Seq[ResolvedTarget]): immutable.Iterable[ResolvedTarget] = {
 
     // if the user has specified a port name in the search, don't do any filtering and assume it
     // is handled in the service discovery mechanism
     if (lookup.portName.isDefined || !filterOnFallbackPort) {
       contactPoints
     } else {
       contactPoints.groupBy(_.host).flatMap {
-        case (_, immutable.Seq(singleResult)) =>
-          immutable.Seq(singleResult)
+        case (_, Seq(singleResult)) =>
+          Seq(singleResult)
         case (_, multipleResults) =>
           if (multipleResults.exists(_.port.isDefined)) {
             multipleResults.filter(_.port.contains(fallbackPort))

management-cluster-http/src/main/scala/org/apache/pekko/management/cluster/ClusterHttpManagementProtocol.scala

@@ -20,22 +20,22 @@ import spray.json.{ DefaultJsonProtocol, RootJsonFormat }
 
 import scala.collection.immutable
 
-final case class ClusterUnreachableMember(node: String, observedBy: immutable.Seq[String])
+final case class ClusterUnreachableMember(node: String, observedBy: Seq[String])
 final case class ClusterMember(node: String, nodeUid: String, status: String, roles: Set[String])
 object ClusterMember {
   implicit val clusterMemberOrdering: Ordering[ClusterMember] = Ordering.by(_.node)
 }
 final case class ClusterMembers(
     selfNode: String,
     members: Set[ClusterMember],
-    unreachable: immutable.Seq[ClusterUnreachableMember],
+    unreachable: Seq[ClusterUnreachableMember],
     leader: Option[String],
     oldest: Option[String],
     oldestPerRole: Map[String, String])
 final case class ClusterHttpManagementMessage(message: String)
 final case class ShardEntityTypeKeys(entityTypeKeys: immutable.Set[String])
 final case class ShardRegionInfo(shardId: String, numEntities: Int)
-final case class ShardDetails(regions: immutable.Seq[ShardRegionInfo])
+final case class ShardDetails(regions: Seq[ShardRegionInfo])
 
 /** INTERNAL API */
 @InternalApi private[pekko] sealed trait ClusterHttpManagementMemberOperation

management-cluster-http/src/test/scala/org/apache/pekko/cluster/http/management/scaladsl/ClusterHttpManagementRoutesSpec.scala

@@ -41,7 +41,7 @@ import org.scalatest.matchers.should.Matchers
 import org.scalatest.time.{ Millis, Seconds, Span }
 import org.scalatest.wordspec.AnyWordSpecLike
 
-import scala.collection.immutable._
+import scala.collection.immutable.SortedSet
 import scala.concurrent.Promise
 
 class ClusterHttpManagementRoutesSpec

management/src/main/scala/org/apache/pekko/management/HealthCheckSettings.scala

@@ -15,7 +15,6 @@ package org.apache.pekko.management
 
 import com.typesafe.config.Config
 
-import scala.collection.immutable
 import scala.concurrent.duration.FiniteDuration
 import scala.jdk.CollectionConverters._
 import scala.jdk.DurationConverters._
@@ -119,18 +118,18 @@ object HealthCheckSettings {
  * @param checkTimeout how long to wait for all health checks to complete
  */
 final class HealthCheckSettings(
-    val startupChecks: immutable.Seq[NamedHealthCheck],
-    val readinessChecks: immutable.Seq[NamedHealthCheck],
-    val livenessChecks: immutable.Seq[NamedHealthCheck],
+    val startupChecks: Seq[NamedHealthCheck],
+    val readinessChecks: Seq[NamedHealthCheck],
+    val livenessChecks: Seq[NamedHealthCheck],
     val startupPath: String,
     val readinessPath: String,
     val livenessPath: String,
     val checkTimeout: FiniteDuration) {
 
   @deprecated("Use constructor that takes `startupChecks` and `startupPath` parameters instead", "1.1.0")
   def this(
-      readinessChecks: immutable.Seq[NamedHealthCheck],
-      livenessChecks: immutable.Seq[NamedHealthCheck],
+      readinessChecks: Seq[NamedHealthCheck],
+      livenessChecks: Seq[NamedHealthCheck],
       readinessPath: String,
       livenessPath: String,
       checkTimeout: FiniteDuration

management/src/main/scala/org/apache/pekko/management/PekkoManagementSettings.scala

@@ -16,7 +16,6 @@ package org.apache.pekko.management
 import java.net.InetAddress
 import java.util.Optional
 
-import scala.collection.immutable
 import scala.concurrent.duration.{ Duration, FiniteDuration }
 import scala.jdk.CollectionConverters._
 import scala.jdk.DurationConverters._
@@ -62,7 +61,7 @@ final class PekkoManagementSettings(val config: Config) {
     val BasePath: Option[String] =
       Option(cc.getString("base-path")).flatMap(it => if (it.trim == "") None else Some(it))
 
-    val RouteProviders: immutable.Seq[NamedRouteProvider] = {
+    val RouteProviders: Seq[NamedRouteProvider] = {
       def validFQCN(value: Any) = {
         value != null &&
         value != "null" &&

management/src/main/scala/org/apache/pekko/management/internal/HealthChecksImpl.scala

@@ -28,7 +28,6 @@ import pekko.management.javadsl.{ ReadinessCheckSetup => JReadinessCheckSetup }
 import pekko.management.javadsl.{ StartupCheckSetup => JStartupCheckSetup }
 import pekko.management.scaladsl.{ HealthChecks, LivenessCheckSetup, ReadinessCheckSetup, StartupCheckSetup }
 
-import scala.collection.immutable
 import scala.concurrent.Future
 import scala.jdk.CollectionConverters._
 import scala.jdk.FutureConverters._
@@ -59,7 +58,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
     "Loading liveness checks [{}]",
     settings.livenessChecks.map(a => a.name -> a.fullyQualifiedClassName).mkString(", "))
 
-  private val startupChecks: immutable.Seq[HealthCheck] = {
+  private val startupChecks: Seq[HealthCheck] = {
     val fromScaladslSetup = system.settings.setup.get[StartupCheckSetup] match {
       case None        => Nil
       case Some(setup) => setup.createHealthChecks(system)
@@ -72,7 +71,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
     fromConfig ++ fromScaladslSetup ++ fromJavadslSetup
   }
 
-  private val readiness: immutable.Seq[HealthCheck] = {
+  private val readiness: Seq[HealthCheck] = {
     val fromScaladslSetup = system.settings.setup.get[ReadinessCheckSetup] match {
       case None        => Nil
       case Some(setup) => setup.createHealthChecks(system)
@@ -85,7 +84,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
     fromConfig ++ fromScaladslSetup ++ fromJavadslSetup
   }
 
-  private val liveness: immutable.Seq[HealthCheck] = {
+  private val liveness: Seq[HealthCheck] = {
     val fromScaladslSetup = system.settings.setup.get[LivenessCheckSetup] match {
       case None        => Nil
       case Some(setup) => setup.createHealthChecks(system)
@@ -99,7 +98,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
   }
 
   private def convertSuppliersToScala(
-      suppliers: JList[Supplier[CompletionStage[JBoolean]]]): immutable.Seq[HealthCheck] = {
+      suppliers: JList[Supplier[CompletionStage[JBoolean]]]): Seq[HealthCheck] = {
     suppliers.asScala.toList.map(convertSupplierToScala)
   }
 
@@ -111,7 +110,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
     system.dynamicAccess
       .createInstanceFor[HealthCheck](
         fqcn,
-        immutable.Seq((classOf[ActorSystem], system)))
+        Seq((classOf[ActorSystem], system)))
       .recoverWith {
         case _: NoSuchMethodException =>
           system.dynamicAccess.createInstanceFor[HealthCheck](fqcn, Nil)
@@ -122,7 +121,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
     system.dynamicAccess
       .createInstanceFor[Supplier[CompletionStage[JBoolean]]](
         fqcn,
-        immutable.Seq((classOf[ActorSystem], system)))
+        Seq((classOf[ActorSystem], system)))
       .recoverWith {
         case _: NoSuchMethodException =>
           system.dynamicAccess.createInstanceFor[Supplier[CompletionStage[JBoolean]]](fqcn, Nil)
@@ -131,7 +130,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
   }
 
   private def load(
-      checks: immutable.Seq[NamedHealthCheck]): immutable.Seq[HealthCheck] = {
+      checks: Seq[NamedHealthCheck]): Seq[HealthCheck] = {
     checks
       .map(namedHealthCheck =>
         tryLoadScalaHealthCheck(namedHealthCheck.fullyQualifiedClassName).recoverWith {
@@ -202,7 +201,7 @@ final private[pekko] class HealthChecksImpl(system: ExtendedActorSystem, setting
     Future.fromTry(Try(check())).flatMap(identity)
   }
 
-  private def check(checks: immutable.Seq[HealthCheck]): Future[Either[String, Unit]] = {
+  private def check(checks: Seq[HealthCheck]): Future[Either[String, Unit]] = {
     val spawnedChecks: Seq[Future[Either[String, Unit]]] = checks.map { check =>
       val checkName = check.getClass.getName
       // Create a per-check timeout so each check gets its own timer,