diff --git a/R/pkg/tests/fulltests/test_client.R b/R/pkg/tests/fulltests/test_client.R
index 9798627ffc551..b38067e534fc0 100644
--- a/R/pkg/tests/fulltests/test_client.R
+++ b/R/pkg/tests/fulltests/test_client.R
@@ -37,7 +37,7 @@ test_that("multiple packages don't produce a warning", {
 
 test_that("sparkJars sparkPackages as character vectors", {
   args <- generateSparkSubmitArgs("", "", c("one.jar", "two.jar", "three.jar"), "",
-                                  c("com.databricks:spark-avro_2.12:2.0.1"))
+                                  c("com.databricks:spark-avro_2.13:2.0.1"))
   expect_match(args, "--jars one.jar,two.jar,three.jar")
-  expect_match(args, "--packages com.databricks:spark-avro_2.12:2.0.1")
+  expect_match(args, "--packages com.databricks:spark-avro_2.13:2.0.1")
 })
diff --git a/common/kvstore/pom.xml b/common/kvstore/pom.xml
index 66e6bb473bf2f..d356958a3f701 100644
--- a/common/kvstore/pom.xml
+++ b/common/kvstore/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.13</artifactId>
     <version>3.5.1</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-kvstore_2.12</artifactId>
+  <artifactId>spark-kvstore_2.13</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Local DB</name>
   <url>https://spark.apache.org/</url>
diff --git a/common/network-common/pom.xml b/common/network-common/pom.xml
index 98897b4424ae0..4fe3fdd186b4c 100644
--- a/common/network-common/pom.xml
+++ b/common/network-common/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.13</artifactId>
     <version>3.5.1</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-network-common_2.12</artifactId>
+  <artifactId>spark-network-common_2.13</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Networking</name>
   <url>https://spark.apache.org/</url>
diff --git a/common/network-shuffle/pom.xml b/common/network-shuffle/pom.xml
index 44531ea54cd58..ce04c865a0ac1 100644
--- a/common/network-shuffle/pom.xml
+++ b/common/network-shuffle/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.13</artifactId>
     <version>3.5.1</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-network-shuffle_2.12</artifactId>
+  <artifactId>spark-network-shuffle_2.13</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Shuffle Streaming Service</name>
   <url>https://spark.apache.org/</url>
diff --git a/common/unsafe/pom.xml b/common/unsafe/pom.xml
index bf116a6ff12e7..449b24818bbe0 100644
--- a/common/unsafe/pom.xml
+++ b/common/unsafe/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.13</artifactId>
     <version>3.5.1</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-unsafe_2.12</artifactId>
+  <artifactId>spark-unsafe_2.13</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Unsafe</name>
   <url>https://spark.apache.org/</url>
diff --git a/connector/docker-integration-tests/pom.xml b/connector/docker-integration-tests/pom.xml
index 898e1f88c7783..b4971790164ff 100644
--- a/connector/docker-integration-tests/pom.xml
+++ b/connector/docker-integration-tests/pom.xml
@@ -21,12 +21,12 @@
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.spark</groupId>
-    <artifactId>spark-parent_2.12</artifactId>
+    <artifactId>spark-parent_2.13</artifactId>
     <version>3.5.1</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>
 
-  <artifactId>spark-docker-integration-tests_2.12</artifactId>
+  <artifactId>spark-docker-integration-tests_2.13</artifactId>
   <packaging>jar</packaging>
   <name>Spark Project Docker Integration Tests</name>
   <url>https://spark.apache.org/</url>
diff --git a/connector/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/JsonUtils.scala b/connector/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/JsonUtils.scala
index 6dd5af2389a81..4f1c76c7a7fe3 100644
--- a/connector/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/JsonUtils.scala
+++ b/connector/kafka-0-10-sql/src/main/scala/org/apache/spark/sql/kafka010/JsonUtils.scala
@@ -21,14 +21,14 @@ import scala.collection.mutable.HashMap
 import scala.util.control.NonFatal
 
 import org.apache.kafka.common.TopicPartition
-import org.json4s.NoTypeHints
+import org.json4s.{Formats, NoTypeHints}
 import org.json4s.jackson.Serialization
 
 /**
  * Utilities for converting Kafka related objects to and from json.
  */
 private object JsonUtils {
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
 
   /**
    * Read TopicPartitions from json string
@@ -96,10 +96,8 @@ private object JsonUtils {
    */
   def partitionOffsets(partitionOffsets: Map[TopicPartition, Long]): String = {
     val result = new HashMap[String, HashMap[Int, Long]]()
-    implicit val order = new Ordering[TopicPartition] {
-      override def compare(x: TopicPartition, y: TopicPartition): Int = {
+    implicit val order: Ordering[TopicPartition] = (x: TopicPartition, y: TopicPartition) => {
         Ordering.Tuple2[String, Int].compare((x.topic, x.partition), (y.topic, y.partition))
-      }
     }
     val partitions = partitionOffsets.keySet.toSeq.sorted  // sort for more determinism
     partitions.foreach { tp =>
diff --git a/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala b/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala
index 7209e2c373ab1..d6a50ff84f562 100644
--- a/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala
@@ -30,6 +30,7 @@ import scala.concurrent.ExecutionContext.Implicits.global
 import scala.concurrent.duration._
 import scala.sys.process._
 
+import org.json4s.Formats
 import org.json4s.jackson.JsonMethods
 
 import org.apache.spark.{SparkConf, SparkContext}
@@ -340,7 +341,7 @@ private object FaultToleranceTest extends App with Logging {
 private class TestMasterInfo(val ip: String, val dockerId: DockerId, val logFile: File)
   extends Logging  {
 
-  implicit val formats = org.json4s.DefaultFormats
+  implicit val formats: Formats = org.json4s.DefaultFormats
   var state: RecoveryState.Value = _
   var liveWorkerIPs: List[String] = _
   var numLiveApps = 0
@@ -383,7 +384,7 @@ private class TestMasterInfo(val ip: String, val dockerId: DockerId, val logFile
 private class TestWorkerInfo(val ip: String, val dockerId: DockerId, val logFile: File)
   extends Logging {
 
-  implicit val formats = org.json4s.DefaultFormats
+  implicit val formats: Formats = org.json4s.DefaultFormats
 
   logDebug("Created worker: " + this)
 
diff --git a/core/src/main/scala/org/apache/spark/deploy/StandaloneResourceUtils.scala b/core/src/main/scala/org/apache/spark/deploy/StandaloneResourceUtils.scala
index 641c5416cbb33..2e4e07b36cb64 100644
--- a/core/src/main/scala/org/apache/spark/deploy/StandaloneResourceUtils.scala
+++ b/core/src/main/scala/org/apache/spark/deploy/StandaloneResourceUtils.scala
@@ -23,7 +23,7 @@ import java.nio.file.Files
 import scala.collection.mutable
 import scala.util.control.NonFatal
 
-import org.json4s.{DefaultFormats, Extraction}
+import org.json4s.{DefaultFormats, Extraction, Formats}
 import org.json4s.jackson.JsonMethods.{compact, render}
 
 import org.apache.spark.SparkException
@@ -114,7 +114,7 @@ private[spark] object StandaloneResourceUtils extends Logging {
   private def writeResourceAllocationJson[T](
       allocations: Seq[T],
       jsonFile: File): Unit = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val allocationJson = Extraction.decompose(allocations)
     Files.write(jsonFile.toPath, compact(render(allocationJson)).getBytes())
   }
diff --git a/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala b/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
index 537522326fc78..f98a2ab974c2f 100644
--- a/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
+++ b/core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala
@@ -60,8 +60,6 @@ private[spark] class CoarseGrainedExecutorBackend(
 
   import CoarseGrainedExecutorBackend._
 
-  private implicit val formats = DefaultFormats
-
   private[spark] val stopping = new AtomicBoolean(false)
   var executor: Executor = null
   @volatile var driver: Option[RpcEndpointRef] = None
diff --git a/core/src/main/scala/org/apache/spark/resource/ResourceInformation.scala b/core/src/main/scala/org/apache/spark/resource/ResourceInformation.scala
index 7f7bb36512d14..0201708468e5f 100644
--- a/core/src/main/scala/org/apache/spark/resource/ResourceInformation.scala
+++ b/core/src/main/scala/org/apache/spark/resource/ResourceInformation.scala
@@ -19,7 +19,7 @@ package org.apache.spark.resource
 
 import scala.util.control.NonFatal
 
-import org.json4s.{DefaultFormats, Extraction, JValue}
+import org.json4s.{DefaultFormats, Extraction, JValue, Formats}
 import org.json4s.jackson.JsonMethods._
 
 import org.apache.spark.SparkException
@@ -69,7 +69,7 @@ private[spark] object ResourceInformation {
    * Parses a JSON string into a [[ResourceInformation]] instance.
    */
   def parseJson(json: String): ResourceInformation = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     try {
       parse(json).extract[ResourceInformationJson].toResourceInformation
     } catch {
@@ -80,7 +80,7 @@ private[spark] object ResourceInformation {
   }
 
   def parseJson(json: JValue): ResourceInformation = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     try {
       json.extract[ResourceInformationJson].toResourceInformation
     } catch {
diff --git a/core/src/main/scala/org/apache/spark/resource/ResourceUtils.scala b/core/src/main/scala/org/apache/spark/resource/ResourceUtils.scala
index d19f413598b58..095b015a28632 100644
--- a/core/src/main/scala/org/apache/spark/resource/ResourceUtils.scala
+++ b/core/src/main/scala/org/apache/spark/resource/ResourceUtils.scala
@@ -22,7 +22,7 @@ import java.util.Optional
 
 import scala.util.control.NonFatal
 
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.jackson.JsonMethods._
 
 import org.apache.spark.{SparkConf, SparkException}
@@ -252,7 +252,7 @@ private[spark] object ResourceUtils extends Logging {
 
   def parseAllocatedFromJsonFile(resourcesFile: String): Seq[ResourceAllocation] = {
     withResourcesJson[ResourceAllocation](resourcesFile) { json =>
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       parse(json).extract[Seq[ResourceAllocation]]
     }
   }
diff --git a/core/src/main/scala/org/apache/spark/status/AppStatusSource.scala b/core/src/main/scala/org/apache/spark/status/AppStatusSource.scala
index d19744db089ba..96dc5ac44b47a 100644
--- a/core/src/main/scala/org/apache/spark/status/AppStatusSource.scala
+++ b/core/src/main/scala/org/apache/spark/status/AppStatusSource.scala
@@ -31,7 +31,7 @@ private [spark] class JobDuration(val value: AtomicLong) extends Gauge[Long] {
 
 private[spark] class AppStatusSource extends Source {
 
-  override implicit val metricRegistry = new MetricRegistry()
+  override implicit val metricRegistry: MetricRegistry = new MetricRegistry()
 
   override val sourceName = "appStatus"
 
diff --git a/core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala b/core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala
index 19de4544bea32..6bd01a655608f 100644
--- a/core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala
+++ b/core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala
@@ -23,7 +23,7 @@ import java.util.concurrent.TimeUnit
 
 import scala.collection.JavaConverters._
 import scala.collection.mutable
-import scala.concurrent.{ExecutionContext, Future, TimeoutException}
+import scala.concurrent.{ExecutionContext, ExecutionContextExecutorService, Future, TimeoutException}
 import scala.util.Random
 import scala.util.control.NonFatal
 
@@ -94,7 +94,7 @@ class BlockManagerMasterEndpoint(
 
   private val askThreadPool =
     ThreadUtils.newDaemonCachedThreadPool("block-manager-ask-thread-pool", 100)
-  private implicit val askExecutionContext = ExecutionContext.fromExecutorService(askThreadPool)
+  private implicit val askExecutionContext: ExecutionContextExecutorService = ExecutionContext.fromExecutorService(askThreadPool)
 
   private val topologyMapper = {
     val topologyMapperClassName = conf.get(
diff --git a/core/src/main/scala/org/apache/spark/storage/BlockManagerStorageEndpoint.scala b/core/src/main/scala/org/apache/spark/storage/BlockManagerStorageEndpoint.scala
index 476be80e67df3..775b25f59ad5c 100644
--- a/core/src/main/scala/org/apache/spark/storage/BlockManagerStorageEndpoint.scala
+++ b/core/src/main/scala/org/apache/spark/storage/BlockManagerStorageEndpoint.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.storage
 
-import scala.concurrent.{ExecutionContext, Future}
+import scala.concurrent.{ExecutionContext, ExecutionContextExecutorService, Future}
 
 import org.apache.spark.{MapOutputTracker, SparkEnv}
 import org.apache.spark.internal.Logging
@@ -38,7 +38,7 @@ class BlockManagerStorageEndpoint(
 
   private val asyncThreadPool =
     ThreadUtils.newDaemonCachedThreadPool("block-manager-storage-async-thread-pool", 100)
-  private implicit val asyncExecutionContext = ExecutionContext.fromExecutorService(asyncThreadPool)
+  private implicit val asyncExecutionContext: ExecutionContextExecutorService = ExecutionContext.fromExecutorService(asyncThreadPool)
 
   // Operations that involve removing blocks may be slow and should be done asynchronously
   override def receiveAndReply(context: RpcCallContext): PartialFunction[Any, Unit] = {
diff --git a/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala b/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala
index 5434e82c95b1b..ed67906a4f268 100644
--- a/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/ContextCleanerSuite.scala
@@ -42,7 +42,7 @@ import org.apache.spark.storage._
 abstract class ContextCleanerSuiteBase(val shuffleManager: Class[_] = classOf[SortShuffleManager])
   extends SparkFunSuite with BeforeAndAfter with LocalSparkContext
 {
-  implicit val defaultTimeout = timeout(10.seconds)
+  implicit val defaultTimeout: PatienceConfiguration.Timeout = timeout(10.seconds)
   val conf = new SparkConf()
     .setMaster("local[2]")
     .setAppName("ContextCleanerSuite")
diff --git a/core/src/test/scala/org/apache/spark/SparkContextSuite.scala b/core/src/test/scala/org/apache/spark/SparkContextSuite.scala
index 4145975741bc4..f69e316df5fe8 100644
--- a/core/src/test/scala/org/apache/spark/SparkContextSuite.scala
+++ b/core/src/test/scala/org/apache/spark/SparkContextSuite.scala
@@ -32,7 +32,7 @@ import org.apache.hadoop.io.{BytesWritable, LongWritable, Text}
 import org.apache.hadoop.mapred.TextInputFormat
 import org.apache.hadoop.mapreduce.lib.input.{TextInputFormat => NewTextInputFormat}
 import org.apache.logging.log4j.{Level, LogManager}
-import org.json4s.{DefaultFormats, Extraction}
+import org.json4s.{DefaultFormats, Extraction, Formats}
 import org.scalatest.concurrent.Eventually
 import org.scalatest.matchers.must.Matchers._
 
@@ -923,7 +923,7 @@ class SparkContextSuite extends SparkFunSuite with LocalSparkContext with Eventu
       val scriptPath = createTempScriptWithExpectedOutput(dir, "gpuDiscoveryScript",
         """{"name": "gpu","addresses":["5", "6"]}""")
 
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val gpusAllocated =
         ResourceAllocation(DRIVER_GPU_ID, Seq("0", "1", "8"))
       val ja = Extraction.decompose(Seq(gpusAllocated))
diff --git a/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerSuite.scala b/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerSuite.scala
index 6322661f4afd2..a83a0ace5c008 100644
--- a/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/history/HistoryServerSuite.scala
@@ -29,6 +29,7 @@ import scala.concurrent.duration._
 import com.google.common.io.{ByteStreams, Files}
 import org.apache.commons.io.{FileUtils, IOUtils}
 import org.apache.hadoop.fs.{FileStatus, FileSystem, Path}
+import org.json4s.Formats
 import org.json4s.JsonAST._
 import org.json4s.jackson.JsonMethods
 import org.json4s.jackson.JsonMethods._
@@ -380,7 +381,7 @@ abstract class HistoryServerSuite extends SparkFunSuite with BeforeAndAfter with
 
   test("incomplete apps get refreshed") {
     implicit val webDriver: WebDriver = new HtmlUnitDriver
-    implicit val formats = org.json4s.DefaultFormats
+    implicit val formats: Formats = org.json4s.DefaultFormats
 
     // this test dir is explicitly deleted on successful runs; retained for diagnostics when
     // not
diff --git a/core/src/test/scala/org/apache/spark/deploy/master/MasterSuite.scala b/core/src/test/scala/org/apache/spark/deploy/master/MasterSuite.scala
index 37874de987662..f3c7138a13119 100644
--- a/core/src/test/scala/org/apache/spark/deploy/master/MasterSuite.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/master/MasterSuite.scala
@@ -327,7 +327,7 @@ class MasterSuite extends SparkFunSuite
   }
 
   test("SPARK-46888: master should reject worker kill request if decommision is disabled") {
-    implicit val formats = org.json4s.DefaultFormats
+    implicit val formats: Formats = org.json4s.DefaultFormats
     val conf = new SparkConf()
       .set(DECOMMISSION_ENABLED, false)
       .set(MASTER_UI_DECOMMISSION_ALLOW_MODE, "ALLOW")
@@ -347,7 +347,7 @@ class MasterSuite extends SparkFunSuite
   }
 
   test("master/worker web ui available") {
-    implicit val formats = org.json4s.DefaultFormats
+    implicit val formats: Formats = org.json4s.DefaultFormats
     val conf = new SparkConf()
     val localCluster = LocalSparkCluster(2, 2, 512, conf)
     localCluster.start()
@@ -383,7 +383,7 @@ class MasterSuite extends SparkFunSuite
   }
 
   test("master/worker web ui available with reverseProxy") {
-    implicit val formats = org.json4s.DefaultFormats
+    implicit val formats: Formats = org.json4s.DefaultFormats
     val conf = new SparkConf()
     conf.set(UI_REVERSE_PROXY, true)
     val localCluster = LocalSparkCluster(2, 2, 512, conf)
@@ -419,7 +419,7 @@ class MasterSuite extends SparkFunSuite
   }
 
   test("master/worker web ui available behind front-end reverseProxy") {
-    implicit val formats = org.json4s.DefaultFormats
+    implicit val formats: Formats = org.json4s.DefaultFormats
     val reverseProxyUrl = "http://proxyhost:8080/path/to/spark"
     val conf = new SparkConf()
     conf.set(UI_REVERSE_PROXY, true)
diff --git a/core/src/test/scala/org/apache/spark/deploy/worker/WorkerSuite.scala b/core/src/test/scala/org/apache/spark/deploy/worker/WorkerSuite.scala
index a07d4f76905a7..75cebc90acba5 100644
--- a/core/src/test/scala/org/apache/spark/deploy/worker/WorkerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/worker/WorkerSuite.scala
@@ -23,7 +23,7 @@ import java.util.function.Supplier
 
 import scala.concurrent.duration._
 
-import org.json4s.{DefaultFormats, Extraction}
+import org.json4s.{DefaultFormats, Extraction, Formats}
 import org.mockito.{Mock, MockitoAnnotations}
 import org.mockito.Answers.RETURNS_SMART_NULLS
 import org.mockito.ArgumentMatchers.any
@@ -60,7 +60,7 @@ class WorkerSuite extends SparkFunSuite with Matchers with BeforeAndAfter {
   }
   def conf(opts: (String, String)*): SparkConf = new SparkConf(loadDefaults = false).setAll(opts)
 
-  implicit val formats = DefaultFormats
+  implicit val formats: Formats = DefaultFormats
 
   private var _worker: Worker = _
 
diff --git a/core/src/test/scala/org/apache/spark/executor/CoarseGrainedExecutorBackendSuite.scala b/core/src/test/scala/org/apache/spark/executor/CoarseGrainedExecutorBackendSuite.scala
index 909d605442575..57d391b0cf063 100644
--- a/core/src/test/scala/org/apache/spark/executor/CoarseGrainedExecutorBackendSuite.scala
+++ b/core/src/test/scala/org/apache/spark/executor/CoarseGrainedExecutorBackendSuite.scala
@@ -26,7 +26,7 @@ import java.util.concurrent.atomic.AtomicInteger
 import scala.collection.concurrent.TrieMap
 import scala.concurrent.duration._
 
-import org.json4s.{DefaultFormats, Extraction}
+import org.json4s.{DefaultFormats, Extraction, Formats}
 import org.json4s.JsonAST.{JArray, JObject}
 import org.json4s.JsonDSL._
 import org.mockito.ArgumentMatchers.any
@@ -50,7 +50,7 @@ import org.apache.spark.util.{SerializableBuffer, ThreadUtils, Utils}
 class CoarseGrainedExecutorBackendSuite extends SparkFunSuite
     with LocalSparkContext with MockitoSugar {
 
-  implicit val formats = DefaultFormats
+  implicit val formats: Formats = DefaultFormats
 
   test("parsing no resources") {
     val conf = new SparkConf
diff --git a/core/src/test/scala/org/apache/spark/resource/ResourceUtilsSuite.scala b/core/src/test/scala/org/apache/spark/resource/ResourceUtilsSuite.scala
index ffe5ff5787102..e2daf41a203c2 100644
--- a/core/src/test/scala/org/apache/spark/resource/ResourceUtilsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/resource/ResourceUtilsSuite.scala
@@ -21,7 +21,7 @@ import java.io.File
 import java.nio.file.{Files => JavaFiles}
 import java.util.Optional
 
-import org.json4s.{DefaultFormats, Extraction}
+import org.json4s.{DefaultFormats, Extraction, Formats}
 
 import org.apache.spark.{LocalSparkContext, SparkConf, SparkException, SparkFunSuite}
 import org.apache.spark.TestUtils._
@@ -117,7 +117,7 @@ class ResourceUtilsSuite extends SparkFunSuite
     val conf = new SparkConf
     assume(!(Utils.isWindows))
     withTempDir { dir =>
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val fpgaAddrs = Seq("f1", "f2", "f3")
       val fpgaAllocation = ResourceAllocation(EXECUTOR_FPGA_ID, fpgaAddrs)
       val resourcesFile = createTempJsonFile(
@@ -146,7 +146,7 @@ class ResourceUtilsSuite extends SparkFunSuite
     val rpId = 1
     assume(!(Utils.isWindows))
     withTempDir { dir =>
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val fpgaAddrs = Seq("f1", "f2", "f3")
       val fpgaAllocation = ResourceAllocation(EXECUTOR_FPGA_ID, fpgaAddrs)
       val resourcesFile = createTempJsonFile(
diff --git a/core/src/test/scala/org/apache/spark/ui/UISeleniumSuite.scala b/core/src/test/scala/org/apache/spark/ui/UISeleniumSuite.scala
index 79496bba6674b..32972e860275a 100644
--- a/core/src/test/scala/org/apache/spark/ui/UISeleniumSuite.scala
+++ b/core/src/test/scala/org/apache/spark/ui/UISeleniumSuite.scala
@@ -83,7 +83,7 @@ private[spark] class SparkUICssErrorHandler extends DefaultCssErrorHandler {
 class UISeleniumSuite extends SparkFunSuite with WebBrowser with Matchers {
 
   implicit var webDriver: WebDriver = _
-  implicit val formats = DefaultFormats
+  implicit val formats: Formats = DefaultFormats
 
 
   override def beforeAll(): Unit = {
diff --git a/core/src/test/scala/org/apache/spark/util/KeyLockSuite.scala b/core/src/test/scala/org/apache/spark/util/KeyLockSuite.scala
index 6888e492a8d33..6902493dc3c5d 100644
--- a/core/src/test/scala/org/apache/spark/util/KeyLockSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/KeyLockSuite.scala
@@ -22,14 +22,14 @@ import java.util.concurrent.atomic.AtomicInteger
 
 import scala.concurrent.duration._
 
-import org.scalatest.concurrent.{ThreadSignaler, TimeLimits}
+import org.scalatest.concurrent.{Signaler, ThreadSignaler, TimeLimits}
 
 import org.apache.spark.SparkFunSuite
 
 class KeyLockSuite extends SparkFunSuite with TimeLimits {
 
   // Necessary to make ScalaTest 3.x interrupt a thread on the JVM like ScalaTest 2.2.x
-  private implicit val defaultSignaler = ThreadSignaler
+  private implicit val defaultSignaler: Signaler = ThreadSignaler
 
   private val foreverMs = 60 * 1000L
 
diff --git a/examples/src/main/scala/org/apache/spark/examples/sql/SparkSQLExample.scala b/examples/src/main/scala/org/apache/spark/examples/sql/SparkSQLExample.scala
index b17b86c08314b..669205cb89057 100644
--- a/examples/src/main/scala/org/apache/spark/examples/sql/SparkSQLExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/sql/SparkSQLExample.scala
@@ -17,7 +17,7 @@
 package org.apache.spark.examples.sql
 
 // $example on:programmatic_schema$
-import org.apache.spark.sql.Row
+import org.apache.spark.sql.{Row, Encoder}
 // $example off:programmatic_schema$
 // $example on:init_session$
 import org.apache.spark.sql.SparkSession
@@ -220,7 +220,7 @@ object SparkSQLExample {
     // +------------+
 
     // No pre-defined encoders for Dataset[Map[K,V]], define explicitly
-    implicit val mapEncoder = org.apache.spark.sql.Encoders.kryo[Map[String, Any]]
+    implicit val mapEncoder: Encoder[Map[String, Any]] = org.apache.spark.sql.Encoders.kryo[Map[String, Any]]
     // Primitive types and case classes can be also defined as
     // implicit val stringIntMapEncoder: Encoder[Map[String, Any]] = ExpressionEncoder()
 
diff --git a/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonMatrixConverter.scala b/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonMatrixConverter.scala
index 8f03a29eb991a..a8844358ead2d 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonMatrixConverter.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonMatrixConverter.scala
@@ -16,7 +16,7 @@
  */
 package org.apache.spark.ml.linalg
 
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods.{compact, parse => parseJson, render}
 
@@ -29,7 +29,7 @@ private[ml] object JsonMatrixConverter {
    * Parses the JSON representation of a Matrix into a [[Matrix]].
    */
   def fromJson(json: String): Matrix = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val jValue = parseJson(json)
     (jValue \ "type").extract[Int] match {
       case 0 => // sparse
diff --git a/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonVectorConverter.scala b/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonVectorConverter.scala
index 1b949d75eeaa0..12387233879ad 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonVectorConverter.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/linalg/JsonVectorConverter.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.ml.linalg
 
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods.{compact, parse => parseJson, render}
 
@@ -27,7 +27,7 @@ private[ml] object JsonVectorConverter {
    * Parses the JSON representation of a vector into a [[Vector]].
    */
   def fromJson(json: String): Vector = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val jValue = parseJson(json)
     (jValue \ "type").extract[Int] match {
       case 0 => // sparse
diff --git a/mllib/src/main/scala/org/apache/spark/ml/param/params.scala b/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
index b818be30583c0..1b5845f14f1b0 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
@@ -129,7 +129,7 @@ private[ml] object Param {
       case JObject(v) =>
         val keys = v.map(_._1)
         if (keys.contains("class")) {
-          implicit val formats = DefaultFormats
+          implicit val formats: Formats = DefaultFormats
           val className = (jValue \ "class").extract[String]
           className match {
             case JsonMatrixConverter.className =>
@@ -398,7 +398,7 @@ class IntParam(parent: String, name: String, doc: String, isValid: Int => Boolea
   }
 
   override def jsonDecode(json: String): Int = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     parse(json).extract[Int]
   }
 }
@@ -484,7 +484,7 @@ class LongParam(parent: String, name: String, doc: String, isValid: Long => Bool
   }
 
   override def jsonDecode(json: String): Long = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     parse(json).extract[Long]
   }
 }
@@ -505,7 +505,7 @@ class BooleanParam(parent: String, name: String, doc: String) // No need for isV
   }
 
   override def jsonDecode(json: String): Boolean = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     parse(json).extract[Boolean]
   }
 }
@@ -528,7 +528,7 @@ class StringArrayParam(parent: Params, name: String, doc: String, isValid: Array
   }
 
   override def jsonDecode(json: String): Array[String] = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     parse(json).extract[Seq[String]].toArray
   }
 }
@@ -617,7 +617,7 @@ class IntArrayParam(parent: Params, name: String, doc: String, isValid: Array[In
   }
 
   override def jsonDecode(json: String): Array[Int] = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     parse(json).extract[Seq[Int]].toArray
   }
 }
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/classification/ClassificationModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/classification/ClassificationModel.scala
index 5161bc72659c6..97de8604e7728 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/classification/ClassificationModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/classification/ClassificationModel.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.mllib.classification
 
-import org.json4s.{DefaultFormats, JValue}
+import org.json4s.{DefaultFormats, JValue, Formats}
 
 import org.apache.spark.annotation.Since
 import org.apache.spark.api.java.JavaRDD
@@ -65,7 +65,7 @@ private[mllib] object ClassificationModel {
    * @return (numFeatures, numClasses)
    */
   def getNumFeaturesClasses(metadata: JValue): (Int, Int) = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     ((metadata \ "numFeatures").extract[Int], (metadata \ "numClasses").extract[Int])
   }
 }
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/BisectingKMeansModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/BisectingKMeansModel.scala
index c3979118de403..2d1781a25d3f6 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/BisectingKMeansModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/BisectingKMeansModel.scala
@@ -18,7 +18,7 @@
 package org.apache.spark.mllib.clustering
 
 import org.json4s._
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods._
 
@@ -187,7 +187,7 @@ object BisectingKMeansModel extends Loader[BisectingKMeansModel] {
     }
 
     def load(sc: SparkContext, path: String): BisectingKMeansModel = {
-      implicit val formats: DefaultFormats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
       assert(className == thisClassName)
       assert(formatVersion == thisFormatVersion)
@@ -223,7 +223,7 @@ object BisectingKMeansModel extends Loader[BisectingKMeansModel] {
     }
 
     def load(sc: SparkContext, path: String): BisectingKMeansModel = {
-      implicit val formats: DefaultFormats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
       assert(className == thisClassName)
       assert(formatVersion == thisFormatVersion)
@@ -261,7 +261,7 @@ object BisectingKMeansModel extends Loader[BisectingKMeansModel] {
     }
 
     def load(sc: SparkContext, path: String): BisectingKMeansModel = {
-      implicit val formats: DefaultFormats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
       assert(className == thisClassName)
       assert(formatVersion == thisFormatVersion)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/GaussianMixtureModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/GaussianMixtureModel.scala
index 0c9c6ab826e62..eb5e776799d04 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/GaussianMixtureModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/GaussianMixtureModel.scala
@@ -18,7 +18,7 @@
 package org.apache.spark.mllib.clustering
 
 import breeze.linalg.{DenseVector => BreezeVector}
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods._
 
@@ -175,7 +175,7 @@ object GaussianMixtureModel extends Loader[GaussianMixtureModel] {
   @Since("1.4.0")
   override def load(sc: SparkContext, path: String): GaussianMixtureModel = {
     val (loadedClassName, version, metadata) = Loader.loadMetadata(sc, path)
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val k = (metadata \ "k").extract[Int]
     val classNameV1_0 = SaveLoadV1_0.classNameV1_0
     (loadedClassName, version) match {
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeansModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeansModel.scala
index 64b352157caf7..5eafdc9add58d 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeansModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/KMeansModel.scala
@@ -179,7 +179,7 @@ object KMeansModel extends Loader[KMeansModel] {
     }
 
     def load(sc: SparkContext, path: String): KMeansModel = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
       assert(className == thisClassName)
@@ -213,7 +213,7 @@ object KMeansModel extends Loader[KMeansModel] {
     }
 
     def load(sc: SparkContext, path: String): KMeansModel = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
       assert(className == thisClassName)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAModel.scala
index aa8b6a00a427f..e318f06900950 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/LDAModel.scala
@@ -20,7 +20,7 @@ package org.apache.spark.mllib.clustering
 import breeze.linalg.{argmax, argtopk, normalize, sum, DenseMatrix => BDM, DenseVector => BDV}
 import breeze.numerics.{exp, lgamma}
 import org.apache.hadoop.fs.Path
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods._
 
@@ -496,7 +496,7 @@ object LocalLDAModel extends Loader[LocalLDAModel] {
   @Since("1.5.0")
   override def load(sc: SparkContext, path: String): LocalLDAModel = {
     val (loadedClassName, loadedVersion, metadata) = Loader.loadMetadata(sc, path)
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val expectedK = (metadata \ "k").extract[Int]
     val expectedVocabSize = (metadata \ "vocabSize").extract[Int]
     val docConcentration =
@@ -923,7 +923,7 @@ object DistributedLDAModel extends Loader[DistributedLDAModel] {
   @Since("1.5.0")
   override def load(sc: SparkContext, path: String): DistributedLDAModel = {
     val (loadedClassName, loadedVersion, metadata) = Loader.loadMetadata(sc, path)
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val expectedK = (metadata \ "k").extract[Int]
     val vocabSize = (metadata \ "vocabSize").extract[Int]
     val docConcentration =
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala b/mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala
index ba541bbcccd29..12c7ae5066c82 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/clustering/PowerIterationClustering.scala
@@ -79,7 +79,7 @@ object PowerIterationClusteringModel extends Loader[PowerIterationClusteringMode
 
     @Since("1.4.0")
     def load(sc: SparkContext, path: String): PowerIterationClusteringModel = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
 
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala b/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala
index 3202f08e220b0..4aae9d8add43a 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala
@@ -145,7 +145,7 @@ object ChiSqSelectorModel extends Loader[ChiSqSelectorModel] {
     }
 
     def load(sc: SparkContext, path: String): ChiSqSelectorModel = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
       assert(className == thisClassName)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala b/mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala
index 97f277d53ca9d..f286b729c03d0 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala
@@ -23,7 +23,7 @@ import scala.collection.JavaConverters._
 import scala.collection.mutable
 
 import com.google.common.collect.{Ordering => GuavaOrdering}
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods._
 
@@ -704,7 +704,7 @@ object Word2VecModel extends Loader[Word2VecModel] {
   override def load(sc: SparkContext, path: String): Word2VecModel = {
 
     val (loadedClassName, loadedVersion, metadata) = Loader.loadMetadata(sc, path)
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val expectedVectorSize = (metadata \ "vectorSize").extract[Int]
     val expectedNumWords = (metadata \ "numWords").extract[Int]
     val classNameV1_0 = SaveLoadV1_0.classNameV1_0
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/fpm/FPGrowth.scala b/mllib/src/main/scala/org/apache/spark/mllib/fpm/FPGrowth.scala
index ecdc28dea37fd..0938b709226bd 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/fpm/FPGrowth.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/fpm/FPGrowth.scala
@@ -25,7 +25,7 @@ import scala.collection.mutable
 import scala.reflect.ClassTag
 import scala.reflect.runtime.universe._
 
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods.{compact, render}
 
@@ -126,7 +126,7 @@ object FPGrowthModel extends Loader[FPGrowthModel[_]] {
     }
 
     def load(sc: SparkContext, path: String): FPGrowthModel[_] = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
 
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/fpm/PrefixSpan.scala b/mllib/src/main/scala/org/apache/spark/mllib/fpm/PrefixSpan.scala
index 7c023bcfa72a4..703dd65bfab78 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/fpm/PrefixSpan.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/fpm/PrefixSpan.scala
@@ -25,7 +25,7 @@ import scala.collection.mutable
 import scala.reflect.ClassTag
 import scala.reflect.runtime.universe._
 
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods.{compact, render}
 
@@ -670,7 +670,7 @@ object PrefixSpanModel extends Loader[PrefixSpanModel[_]] {
     }
 
     def load(sc: SparkContext, path: String): PrefixSpanModel[_] = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
 
       val (className, formatVersion, metadata) = Loader.loadMetadata(sc, path)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
index a93f37799419e..fa58443cca90b 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala
@@ -25,7 +25,7 @@ import scala.collection.JavaConverters._
 import scala.language.implicitConversions
 
 import breeze.linalg.{DenseVector => BDV, SparseVector => BSV, Vector => BV}
-import org.json4s.DefaultFormats
+import org.json4s.{DefaultFormats, Formats}
 import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods.{compact, parse => parseJson, render}
 
@@ -430,7 +430,7 @@ object Vectors {
    */
   @Since("1.6.0")
   def fromJson(json: String): Vector = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val jValue = parseJson(json)
     (jValue \ "type").extract[Int] match {
       case 0 => // sparse
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/recommendation/MatrixFactorizationModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/recommendation/MatrixFactorizationModel.scala
index 3276513213f5d..581fe1f9eb647 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/recommendation/MatrixFactorizationModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/recommendation/MatrixFactorizationModel.scala
@@ -392,7 +392,7 @@ object MatrixFactorizationModel extends Loader[MatrixFactorizationModel] {
     }
 
     def load(sc: SparkContext, path: String): MatrixFactorizationModel = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       val spark = SparkSession.builder().sparkContext(sc).getOrCreate()
       val (className, formatVersion, metadata) = loadMetadata(sc, path)
       assert(className == thisClassName)
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala b/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala
index 12a78ef4ec140..81d1b290404d5 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala
@@ -209,7 +209,7 @@ object IsotonicRegressionModel extends Loader[IsotonicRegressionModel] {
 
   @Since("1.4.0")
   override def load(sc: SparkContext, path: String): IsotonicRegressionModel = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val (loadedClassName, version, metadata) = loadMetadata(sc, path)
     val isotonic = (metadata \ "isotonic").extract[Boolean]
     val classNameV1_0 = SaveLoadV1_0.thisClassName
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/regression/RegressionModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/regression/RegressionModel.scala
index a95a54225a085..144c2b6a8e852 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/regression/RegressionModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/regression/RegressionModel.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.mllib.regression
 
-import org.json4s.{DefaultFormats, JValue}
+import org.json4s.{DefaultFormats, JValue, Formats}
 
 import org.apache.spark.annotation.Since
 import org.apache.spark.api.java.JavaRDD
@@ -64,7 +64,7 @@ private[mllib] object RegressionModel {
    * @return numFeatures
    */
   def getNumFeatures(metadata: JValue): Int = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     (metadata \ "numFeatures").extract[Int]
   }
 }
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala
index cdc998000c2fc..7a864b9d41efe 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala
@@ -312,7 +312,7 @@ object DecisionTreeModel extends Loader[DecisionTreeModel] with Logging {
    */
   @Since("1.3.0")
   override def load(sc: SparkContext, path: String): DecisionTreeModel = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val (loadedClassName, version, metadata) = Loader.loadMetadata(sc, path)
     val algo = (metadata \ "algo").extract[String]
     val numNodes = (metadata \ "numNodes").extract[Int]
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala
index 1f879a4d9dfbb..03821dc417750 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala
@@ -438,7 +438,7 @@ private[tree] object TreeEnsembleModel extends Logging {
      * Read metadata from the loaded JSON metadata.
      */
     def readMetadata(metadata: JValue): Metadata = {
-      implicit val formats = DefaultFormats
+      implicit val formats: Formats = DefaultFormats
       (metadata \ "metadata").extract[Metadata]
     }
 
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/util/modelSaveLoad.scala b/mllib/src/main/scala/org/apache/spark/mllib/util/modelSaveLoad.scala
index c13bc4099ce70..74e8ae75caf3e 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/util/modelSaveLoad.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/util/modelSaveLoad.scala
@@ -117,7 +117,7 @@ private[mllib] object Loader {
    * @return (class name, version, metadata)
    */
   def loadMetadata(sc: SparkContext, path: String): (String, String, JValue) = {
-    implicit val formats = DefaultFormats
+    implicit val formats: Formats = DefaultFormats
     val metadata = parse(sc.textFile(metadataPath(path)).first())
     val clazz = (metadata \ "class").extract[String]
     val version = (metadata \ "version").extract[String]
diff --git a/resource-managers/yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnSchedulerBackend.scala b/resource-managers/yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnSchedulerBackend.scala
index 34848a7f3d853..3997e5c883ad4 100644
--- a/resource-managers/yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnSchedulerBackend.scala
+++ b/resource-managers/yarn/src/main/scala/org/apache/spark/scheduler/cluster/YarnSchedulerBackend.scala
@@ -21,7 +21,7 @@ import java.util.EnumSet
 import java.util.concurrent.atomic.AtomicBoolean
 import javax.servlet.DispatcherType
 
-import scala.concurrent.{ExecutionContext, Future}
+import scala.concurrent.{ExecutionContext, ExecutionContextExecutorService, Future}
 import scala.util.{Failure, Success}
 import scala.util.control.NonFatal
 
@@ -64,14 +64,14 @@ private[spark] abstract class YarnSchedulerBackend(
   private val yarnSchedulerEndpointRef = rpcEnv.setupEndpoint(
     YarnSchedulerBackend.ENDPOINT_NAME, yarnSchedulerEndpoint)
 
-  private implicit val askTimeout = RpcUtils.askRpcTimeout(sc.conf)
+  private implicit val askTimeout: RpcTimeout = RpcUtils.askRpcTimeout(sc.conf)
 
   /**
    * Declare implicit single thread execution context for futures doRequestTotalExecutors and
    * doKillExecutors below, avoiding using the global execution context that may cause conflict
    * with user code's execution of futures.
    */
-  private implicit val schedulerEndpointEC = ExecutionContext.fromExecutorService(
+  private implicit val schedulerEndpointEC: ExecutionContext = ExecutionContext.fromExecutorService(
       ThreadUtils.newDaemonSingleThreadExecutor("yarn-scheduler-endpoint"))
 
   /** Application ID. */
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ObjectExpressionsSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ObjectExpressionsSuite.scala
index 3a662e68d58c2..33be55a43c52b 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ObjectExpressionsSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ObjectExpressionsSuite.scala
@@ -491,7 +491,7 @@ class ObjectExpressionsSuite extends SparkFunSuite with ExpressionEvalHelper {
     }
   }
 
-  implicit private def mapIntStrEncoder = ExpressionEncoder[Map[Int, String]]()
+  implicit private def mapIntStrEncoder: ExpressionEncoder[Map[Int, String]] = ExpressionEncoder[Map[Int, String]]()
 
   test("SPARK-23588 CatalystToExternalMap should support interpreted execution") {
     // To get a resolved `CatalystToExternalMap` expression, we build a deserializer plan
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ColumnPruningSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ColumnPruningSuite.scala
index f28df3839d0a8..a4d4f0a625e9c 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ColumnPruningSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ColumnPruningSuite.scala
@@ -423,7 +423,7 @@ class ColumnPruningSuite extends PlanTest {
     comparePlans(optimized, expected)
   }
 
-  implicit private def productEncoder[T <: Product : TypeTag] = ExpressionEncoder[T]()
+  implicit private def productEncoder[T <: Product : TypeTag]: ExpressionEncoder[T] = ExpressionEncoder[T]()
   private val func = identity[Iterator[OtherTuple]] _
 
   test("Column pruning on MapPartitions") {
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateMapObjectsSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateMapObjectsSuite.scala
index 1c818eee1224d..f7f429a501aeb 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateMapObjectsSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateMapObjectsSuite.scala
@@ -37,8 +37,8 @@ class EliminateMapObjectsSuite extends PlanTest {
     }
   }
 
-  implicit private def intArrayEncoder = ExpressionEncoder[Array[Int]]()
-  implicit private def doubleArrayEncoder = ExpressionEncoder[Array[Double]]()
+  implicit private def intArrayEncoder: ExpressionEncoder[Array[Int]] = ExpressionEncoder[Array[Int]]()
+  implicit private def doubleArrayEncoder: ExpressionEncoder[Array[Double]] = ExpressionEncoder[Array[Double]]()
 
   test("SPARK-20254: Remove unnecessary data conversion for primitive array") {
     val intObjType = ObjectType(classOf[Array[Int]])
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateSerializationSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateSerializationSuite.scala
index 0d654cc1ac935..a8b4914300bc8 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateSerializationSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateSerializationSuite.scala
@@ -35,8 +35,8 @@ class EliminateSerializationSuite extends PlanTest {
         EliminateSerialization) :: Nil
   }
 
-  implicit private def productEncoder[T <: Product : TypeTag] = ExpressionEncoder[T]()
-  implicit private def intEncoder = ExpressionEncoder[Int]()
+  implicit private def productEncoder[T <: Product : TypeTag]: ExpressionEncoder[T] = ExpressionEncoder[T]()
+  implicit private def intEncoder: ExpressionEncoder[Int] = ExpressionEncoder[Int]()
 
   test("back to back serialization") {
     val input = LocalRelation($"obj".obj(classOf[(Int, Int)]))
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ObjectSerializerPruningSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ObjectSerializerPruningSuite.scala
index a1039b051ce45..02e11343d229a 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ObjectSerializerPruningSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ObjectSerializerPruningSuite.scala
@@ -40,7 +40,7 @@ class ObjectSerializerPruningSuite extends PlanTest {
       RemoveNoopOperators) :: Nil
   }
 
-  implicit private def productEncoder[T <: Product : TypeTag] = ExpressionEncoder[T]()
+  implicit private def productEncoder[T <: Product : TypeTag]: ExpressionEncoder[T] = ExpressionEncoder[T]()
 
   test("collect struct types") {
     val dataTypes = Seq(
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/TypedFilterOptimizationSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/TypedFilterOptimizationSuite.scala
index 4385777e79c09..090ed9af2494c 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/TypedFilterOptimizationSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/TypedFilterOptimizationSuite.scala
@@ -37,7 +37,7 @@ class TypedFilterOptimizationSuite extends PlanTest {
         CombineTypedFilters) :: Nil
   }
 
-  implicit private def productEncoder[T <: Product : TypeTag] = ExpressionEncoder[T]()
+  implicit private def productEncoder[T <: Product : TypeTag]: ExpressionEncoder[T] = ExpressionEncoder[T]()
 
   val testRelation = LocalRelation($"_1".int, $"_2".int)
 
diff --git a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/plans/logical/DistinctKeyVisitorSuite.scala b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/plans/logical/DistinctKeyVisitorSuite.scala
index acf62d07bc398..4979106b5d7fd 100644
--- a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/plans/logical/DistinctKeyVisitorSuite.scala
+++ b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/plans/logical/DistinctKeyVisitorSuite.scala
@@ -47,7 +47,7 @@ class DistinctKeyVisitorSuite extends PlanTest {
     assert(plan.analyze.distinctKeys === distinctKeys)
   }
 
-  implicit private def productEncoder[T <: Product : TypeTag] = ExpressionEncoder[T]()
+  implicit private def productEncoder[T <: Product : TypeTag]: ExpressionEncoder[T] = ExpressionEncoder[T]()
 
   test("Aggregate's distinct attributes") {
     checkDistinctAttributes(t1.groupBy($"a", $"b")($"a", $"b", 1), Set(ExpressionSet(Seq(a, b))))
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala b/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
index c063af9381ff2..0cd24b456fef7 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
@@ -22,6 +22,7 @@ import java.io.{ByteArrayOutputStream, CharArrayWriter, DataOutputStream}
 import scala.annotation.varargs
 import scala.collection.JavaConverters._
 import scala.collection.mutable.{ArrayBuffer, HashSet}
+import scala.reflect.ClassTag
 import scala.reflect.runtime.universe.TypeTag
 import scala.util.control.NonFatal
 
@@ -240,7 +241,7 @@ class Dataset[T] private[sql](
     exprEnc.resolveAndBind(logicalPlan.output, sparkSession.sessionState.analyzer)
   }
 
-  private implicit def classTag = exprEnc.clsTag
+  private implicit def classTag: ClassTag[T] = exprEnc.clsTag
 
   // sqlContext must be val because a stable identifier is expected when you import implicits
   @transient lazy val sqlContext: SQLContext = sparkSession.sqlContext
@@ -1588,7 +1589,7 @@ class Dataset[T] private[sql](
    * @since 1.6.0
    */
   def select[U1](c1: TypedColumn[T, U1]): Dataset[U1] = {
-    implicit val encoder = c1.encoder
+    implicit val encoder: ExpressionEncoder[T] = c1.encoder
     val project = Project(c1.withInputType(exprEnc, logicalPlan.output).named :: Nil, logicalPlan)
 
     if (!encoder.isSerializedAsStructForTopLevel) {
@@ -3383,7 +3384,7 @@ class Dataset[T] private[sql](
    * @since 1.6.0
    */
   def map[U](func: MapFunction[T, U], encoder: Encoder[U]): Dataset[U] = {
-    implicit val uEnc = encoder
+    implicit val uEnc: Encoder[U] = encoder
     withTypedPlan(MapElements[T, U](func, logicalPlan))
   }
 
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/KeyValueGroupedDataset.scala b/sql/core/src/main/scala/org/apache/spark/sql/KeyValueGroupedDataset.scala
index 4c2ccb27eab20..094bc3c8a6901 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/KeyValueGroupedDataset.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/KeyValueGroupedDataset.scala
@@ -43,8 +43,8 @@ class KeyValueGroupedDataset[K, V] private[sql](
     private val groupingAttributes: Seq[Attribute]) extends Serializable {
 
   // Similar to [[Dataset]], we turn the passed in encoder to `ExpressionEncoder` explicitly.
-  private implicit val kExprEnc = encoderFor(kEncoder)
-  private implicit val vExprEnc = encoderFor(vEncoder)
+  private implicit val kExprEnc: ExpressionEncoder[K] = encoderFor(kEncoder)
+  private implicit val vExprEnc: ExpressionEncoder[V] = encoderFor(vEncoder)
 
   private def logicalPlan = queryExecution.analyzed
   private def sparkSession = queryExecution.sparkSession
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceUtils.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceUtils.scala
index a72e4c339af8c..bbc7bd49b4e10 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceUtils.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceUtils.scala
@@ -22,7 +22,7 @@ import java.util.Locale
 import scala.collection.JavaConverters._
 
 import org.apache.hadoop.fs.Path
-import org.json4s.NoTypeHints
+import org.json4s.{NoTypeHints, Formats}
 import org.json4s.jackson.Serialization
 
 import org.apache.spark.SparkUpgradeException
@@ -55,7 +55,7 @@ object DataSourceUtils extends PredicateHelper {
   /**
    * Utility methods for converting partitionBy columns to options and back.
    */
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
 
   def encodePartitioningColumns(columns: Seq[String]): String = {
     Serialization.write(columns)
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ApplyInPandasWithStatePythonRunner.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ApplyInPandasWithStatePythonRunner.scala
index d4c535fe76a3e..2d79d7117bef3 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ApplyInPandasWithStatePythonRunner.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/python/ApplyInPandasWithStatePythonRunner.scala
@@ -204,7 +204,7 @@ class ApplyInPandasWithStatePythonRunner(
         STATE_METADATA_SCHEMA_FROM_PYTHON_WORKER)
 
       stateMetadataBatch.rowIterator().asScala.take(numRows).flatMap { row =>
-        implicit val formats = org.json4s.DefaultFormats
+        implicit val formats: Formats = org.json4s.DefaultFormats
 
         // NOTE: See ApplyInPandasWithStatePythonRunner.STATE_METADATA_SCHEMA_FROM_PYTHON_WORKER
         // for the schema.
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala
index 140367b3236ff..d19ffafb590c9 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/CompactibleFileStreamLog.scala
@@ -24,7 +24,7 @@ import scala.io.{Source => IOSource}
 import scala.reflect.ClassTag
 
 import org.apache.hadoop.fs.Path
-import org.json4s.NoTypeHints
+import org.json4s.{NoTypeHints, Formats}
 import org.json4s.jackson.Serialization
 
 import org.apache.spark.sql.SparkSession
@@ -49,9 +49,10 @@ abstract class CompactibleFileStreamLog[T <: AnyRef : ClassTag](
 
   import CompactibleFileStreamLog._
 
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
 
   /** Needed to serialize type T into JSON when using Jackson */
+  @scala.annotation.nowarn
   private implicit val manifest = Manifest.classType[T](implicitly[ClassTag[T]].runtimeClass)
 
   protected val minBatchesToRetain = sparkSession.sessionState.conf.minBatchesToRetain
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSinkLog.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSinkLog.scala
index 94ba8b8aa5153..d8aa31be47972 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSinkLog.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSinkLog.scala
@@ -18,8 +18,6 @@
 package org.apache.spark.sql.execution.streaming
 
 import org.apache.hadoop.fs.FileStatus
-import org.json4s.NoTypeHints
-import org.json4s.jackson.Serialization
 
 import org.apache.spark.paths.SparkPath
 import org.apache.spark.sql.SparkSession
@@ -90,8 +88,6 @@ class FileStreamSinkLog(
     _retentionMs: Option[Long] = None)
   extends CompactibleFileStreamLog[SinkFileStatus](metadataLogVersion, sparkSession, path) {
 
-  private implicit val formats = Serialization.formats(NoTypeHints)
-
   protected override val fileCleanupDelayMs = sparkSession.sessionState.conf.fileSinkLogCleanupDelay
 
   protected override val isDeletingExpiredLog = sparkSession.sessionState.conf.fileSinkLogDeletion
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSourceLog.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSourceLog.scala
index 5fe9a39c91e0b..42c72f426ea49 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSourceLog.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/FileStreamSourceLog.scala
@@ -22,9 +22,6 @@ import java.util.Map.Entry
 
 import scala.collection.mutable
 
-import org.json4s.NoTypeHints
-import org.json4s.jackson.Serialization
-
 import org.apache.spark.sql.SparkSession
 import org.apache.spark.sql.execution.streaming.FileStreamSource.FileEntry
 import org.apache.spark.sql.internal.SQLConf
@@ -51,8 +48,6 @@ class FileStreamSourceLog(
 
   protected override val isDeletingExpiredLog = sparkSession.sessionState.conf.fileSourceLogDeletion
 
-  private implicit val formats = Serialization.formats(NoTypeHints)
-
   // A fixed size log entry cache to cache the file entries belong to the compaction batch. It is
   // used to avoid scanning the compacted log file to retrieve it's own batch data.
   private val cacheSize = compactInterval
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala
index 3af9c9aebf33d..c9ade7b568e82 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/GroupStateImpl.scala
@@ -246,7 +246,7 @@ private[sql] object GroupStateImpl {
   }
 
   def fromJson[S](value: Option[S], json: JValue): GroupStateImpl[S] = {
-    implicit val formats = org.json4s.DefaultFormats
+    implicit val formats: Formats = org.json4s.DefaultFormats
 
     val hmap = json.extract[Map[String, Any]]
 
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/HDFSMetadataLog.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/HDFSMetadataLog.scala
index 9a811db679d01..b7ea70124d271 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/HDFSMetadataLog.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/HDFSMetadataLog.scala
@@ -26,7 +26,7 @@ import scala.reflect.ClassTag
 
 import org.apache.commons.io.IOUtils
 import org.apache.hadoop.fs._
-import org.json4s.NoTypeHints
+import org.json4s.{NoTypeHints, Formats}
 import org.json4s.jackson.Serialization
 
 import org.apache.spark.internal.Logging
@@ -49,7 +49,7 @@ import org.apache.spark.sql.internal.SQLConf
 class HDFSMetadataLog[T <: AnyRef : ClassTag](sparkSession: SparkSession, path: String)
   extends MetadataLog[T] with Logging {
 
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
 
   /** Needed to serialize type T into JSON when using Jackson */
   private implicit val manifest = Manifest.classType[T](implicitly[ClassTag[T]].runtimeClass)
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousTextSocketSource.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousTextSocketSource.scala
index 368dfae0cc95e..a83054ca8b726 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousTextSocketSource.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousTextSocketSource.scala
@@ -25,7 +25,7 @@ import javax.annotation.concurrent.GuardedBy
 
 import scala.collection.mutable.ListBuffer
 
-import org.json4s.{DefaultFormats, NoTypeHints}
+import org.json4s.{DefaultFormats, NoTypeHints, Formats}
 import org.json4s.jackson.Serialization
 
 import org.apache.spark.SparkEnv
@@ -286,6 +286,6 @@ class TextSocketContinuousPartitionReader(
 }
 
 case class TextSocketOffset(offsets: List[Int]) extends Offset {
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
   override def json: String = Serialization.write(offsets)
 }
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/ContinuousMemoryStream.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/ContinuousMemoryStream.scala
index d0cf602c7cca2..52e5eeb81d3ab 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/ContinuousMemoryStream.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/ContinuousMemoryStream.scala
@@ -22,7 +22,7 @@ import javax.annotation.concurrent.GuardedBy
 
 import scala.collection.mutable.ListBuffer
 
-import org.json4s.NoTypeHints
+import org.json4s.{NoTypeHints, Formats}
 import org.json4s.jackson.Serialization
 
 import org.apache.spark.{SparkEnv, TaskContext}
@@ -46,7 +46,7 @@ import org.apache.spark.util.RpcUtils
 class ContinuousMemoryStream[A : Encoder](id: Int, sqlContext: SQLContext, numPartitions: Int = 2)
   extends MemoryStreamBase[A](sqlContext) with ContinuousStream {
 
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
 
   // ContinuousReader implementation
 
@@ -182,6 +182,6 @@ class ContinuousMemoryStreamPartitionReader(
 
 case class ContinuousMemoryStreamOffset(partitionNums: Map[Int, Int])
   extends Offset {
-  private implicit val formats = Serialization.formats(NoTypeHints)
+  private implicit val formats: Formats = Serialization.formats(NoTypeHints)
   override def json(): String = Serialization.write(partitionNums)
 }
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/RatePerMicroBatchStream.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/RatePerMicroBatchStream.scala
index 6954e4534e494..bc74be538d90f 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/RatePerMicroBatchStream.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/sources/RatePerMicroBatchStream.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.sql.execution.streaming.sources
 
-import org.json4s.NoTypeHints
+import org.json4s.{NoTypeHints, Formats}
 import org.json4s.jackson.Serialization
 
 import org.apache.spark.internal.Logging
@@ -130,7 +130,7 @@ case class RatePerMicroBatchStreamOffset(offset: Long, timestamp: Long) extends
 }
 
 object RatePerMicroBatchStreamOffset {
-  implicit val formats = Serialization.formats(NoTypeHints)
+  implicit val formats: Formats = Serialization.formats(NoTypeHints)
 
   def apply(json: String): RatePerMicroBatchStreamOffset =
     Serialization.read[RatePerMicroBatchStreamOffset](json)
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
index cfeccbdf648c2..dfd193b4349d2 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala
@@ -3748,9 +3748,9 @@ class SQLQuerySuite extends QueryTest with SharedSparkSession with AdaptiveSpark
       .exists(_.contains(s"org.apache.hive.hcatalog_hive-hcatalog-core-$hiveVersion.jar")))
 
     // default transitive=true, test download ivy URL jar return multiple jars
-    sql("ADD JAR ivy://org.scala-js:scalajs-test-interface_2.12:1.2.0")
-    assert(sc.listJars().exists(_.contains("scalajs-library_2.12")))
-    assert(sc.listJars().exists(_.contains("scalajs-test-interface_2.12")))
+    sql("ADD JAR ivy://org.scala-js:scalajs-test-interface_2.13:1.2.0")
+    assert(sc.listJars().exists(_.contains("scalajs-library_2.13")))
+    assert(sc.listJars().exists(_.contains("scalajs-test-interface_2.13")))
 
     sql(s"ADD JAR ivy://org.apache.hive:hive-contrib:$hiveVersion" +
       "?exclude=org.pentaho:pentaho-aggdesigner-algorithm&transitive=true")
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQueryListenerSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQueryListenerSuite.scala
index 52b740bc5c34f..c59e91304c7fa 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQueryListenerSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQueryListenerSuite.scala
@@ -21,7 +21,7 @@ import java.util.UUID
 
 import scala.collection.mutable
 
-import org.scalactic.TolerantNumerics
+import org.scalactic.{Equality, TolerantNumerics}
 import org.scalatest.BeforeAndAfter
 import org.scalatest.concurrent.PatienceConfiguration.Timeout
 import org.scalatest.concurrent.Waiters.Waiter
@@ -44,7 +44,7 @@ class StreamingQueryListenerSuite extends StreamTest with BeforeAndAfter {
   import testImplicits._
 
   // To make === between double tolerate inexact values
-  implicit val doubleEquality = TolerantNumerics.tolerantDoubleEquality(0.01)
+  implicit val doubleEquality: Equality[Double] = TolerantNumerics.tolerantDoubleEquality(0.01)
 
   after {
     spark.streams.active.foreach(_.stop())
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQuerySuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQuerySuite.scala
index 8565056cda6fa..a84690b5b97bb 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQuerySuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingQuerySuite.scala
@@ -29,7 +29,7 @@ import org.apache.commons.io.FileUtils
 import org.apache.commons.lang3.RandomStringUtils
 import org.apache.hadoop.fs.Path
 import org.mockito.Mockito.when
-import org.scalactic.TolerantNumerics
+import org.scalactic.{Equality, TolerantNumerics}
 import org.scalatest.BeforeAndAfter
 import org.scalatest.concurrent.PatienceConfiguration.Timeout
 import org.scalatestplus.mockito.MockitoSugar
@@ -60,7 +60,7 @@ class StreamingQuerySuite extends StreamTest with BeforeAndAfter with Logging wi
   import testImplicits._
 
   // To make === between double tolerate inexact values
-  implicit val doubleEquality = TolerantNumerics.tolerantDoubleEquality(0.01)
+  implicit val doubleEquality: Equality[Double] = TolerantNumerics.tolerantDoubleEquality(0.01)
 
   after {
     sqlContext.streams.active.foreach(_.stop())
diff --git a/sql/core/src/test/scala/org/apache/spark/status/api/v1/sql/SqlResourceWithActualMetricsSuite.scala b/sql/core/src/test/scala/org/apache/spark/status/api/v1/sql/SqlResourceWithActualMetricsSuite.scala
index c63c748953f1a..cceb56bb44111 100644
--- a/sql/core/src/test/scala/org/apache/spark/status/api/v1/sql/SqlResourceWithActualMetricsSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/status/api/v1/sql/SqlResourceWithActualMetricsSuite.scala
@@ -21,7 +21,7 @@ import java.net.URL
 import java.text.SimpleDateFormat
 import javax.servlet.http.HttpServletResponse
 
-import org.json4s.DefaultFormats
+import org.json4s.Formats
 import org.json4s.jackson.JsonMethods
 
 import org.apache.spark.SparkConf
@@ -47,7 +47,7 @@ class SqlResourceWithActualMetricsSuite
   // Exclude nodes which may not have the metrics
   val excludedNodes = List("WholeStageCodegen", "Project", "SerializeFromObject")
 
-  implicit val formats = new DefaultFormats {
+  implicit val formats: DefaultFormats = new DefaultFormats {
     override def dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")
   }
 
diff --git a/sql/hive-thriftserver/src/test/scala/org/apache/spark/sql/hive/thriftserver/HiveThriftServer2Suites.scala b/sql/hive-thriftserver/src/test/scala/org/apache/spark/sql/hive/thriftserver/HiveThriftServer2Suites.scala
index b421a94a06c40..177c9b153e8ae 100644
--- a/sql/hive-thriftserver/src/test/scala/org/apache/spark/sql/hive/thriftserver/HiveThriftServer2Suites.scala
+++ b/sql/hive-thriftserver/src/test/scala/org/apache/spark/sql/hive/thriftserver/HiveThriftServer2Suites.scala
@@ -26,7 +26,7 @@ import java.util.{Locale, UUID}
 import scala.collection.JavaConverters._
 import scala.collection.mutable
 import scala.collection.mutable.ArrayBuffer
-import scala.concurrent.{ExecutionContext, Future, Promise}
+import scala.concurrent.{ExecutionContext, ExecutionContextExecutorService, Future, Promise}
 import scala.concurrent.duration._
 import scala.io.Source
 import scala.util.Try
@@ -441,7 +441,7 @@ class HiveThriftBinaryServerSuite extends HiveThriftServer2Test {
         s"LOAD DATA LOCAL INPATH '${TestData.smallKv}' OVERWRITE INTO TABLE test_map")
 
       queries.foreach(statement.execute)
-      implicit val ec = ExecutionContext.fromExecutorService(
+      implicit val ec: ExecutionContextExecutorService = ExecutionContext.fromExecutorService(
         ThreadUtils.newDaemonSingleThreadExecutor("test-jdbc-cancel"))
       try {
         // Start a very-long-running query that will take hours to finish, then cancel it in order
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/Time.scala b/streaming/src/main/scala/org/apache/spark/streaming/Time.scala
index 92cfd7d40338c..9681245baa0fe 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/Time.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/Time.scala
@@ -89,5 +89,5 @@ case class Time(private val millis: Long) {
 }
 
 object Time {
-  implicit val ordering = Ordering.by((time: Time) => time.millis)
+  implicit val ordering: Ordering[Time] = Ordering.by((time: Time) => time.millis)
 }
diff --git a/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceivedBlockHandler.scala b/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceivedBlockHandler.scala
index 7a561ecb4990f..54bab53a747ac 100644
--- a/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceivedBlockHandler.scala
+++ b/streaming/src/main/scala/org/apache/spark/streaming/receiver/ReceivedBlockHandler.scala
@@ -17,7 +17,7 @@
 
 package org.apache.spark.streaming.receiver
 
-import scala.concurrent.{ExecutionContext, Future}
+import scala.concurrent.{ExecutionContext, ExecutionContextExecutorService, Future}
 import scala.concurrent.duration._
 
 import org.apache.hadoop.conf.Configuration
@@ -159,8 +159,8 @@ private[streaming] class WriteAheadLogBasedBlockHandler(
 
   // For processing futures used in parallel block storing into block manager and write ahead log
   // # threads = 2, so that both writing to BM and WAL can proceed in parallel
-  implicit private val executionContext = ExecutionContext.fromExecutorService(
-    ThreadUtils.newDaemonFixedThreadPool(2, this.getClass.getSimpleName))
+  implicit private val executionContext: ExecutionContextExecutorService = ExecutionContext
+    .fromExecutorService(ThreadUtils.newDaemonFixedThreadPool(2, this.getClass.getSimpleName))
 
   /**
    * This implementation stores the block into the block manager as well as a write ahead log.