Upgrade to Kotlin 1.5

* To align with the rest of Spring portfolio, based on Spring Framework 5.3.x generation,
it is better to upgrade to the Kotlin version supported by SF
* Fix  `ClassUtils.isLambda()` to treat `$inlined$` classes as Kotlin lambdas and let
Java DSL to delegate to the `LambdaMessageProcessor` for better expected type handling.
Looks like Kotlin does not carry type info in its lambdas anymore (at least for functions).
* Add `-parameters` to the compiler args for possible method argument names discovery.
Essentially realign with the rest of portfolio
* Fix Kotlin tests for deprecated API

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-	ext.kotlinVersion = '1.4.32'
+	ext.kotlinVersion = '1.5.30'
 	repositories {
 		mavenCentral()
 		maven { url 'https://plugins.gradle.org/m2' }
@@ -199,12 +199,13 @@ configure(javaProjects) { subproject ->
 
 	compileTestJava {
 		sourceCompatibility = 11
+		targetCompatibility = 11
 		options.encoding = 'UTF-8'
 	}
 
 	compileKotlin {
 		kotlinOptions {
-			languageVersion = '1.3'
+			apiVersion = '1.3'
 			jvmTarget = '1.8'
 			freeCompilerArgs = ['-Xjsr305=strict']
 //			allWarningsAsErrors = true TODO bring it back after upgrading to Kotlin 1.5 language version
@@ -212,7 +213,7 @@ configure(javaProjects) { subproject ->
 	}
 	compileTestKotlin {
 		kotlinOptions {
-			jvmTarget = '1.8'
+			jvmTarget = '11'
 		}
 	}
 
@@ -263,7 +264,7 @@ configure(javaProjects) { subproject ->
 
 	// enable all compiler warnings; individual projects may customize further
 	ext.xLintArg = '-Xlint:all,-options,-processing'
-	[compileJava, compileTestJava]*.options*.compilerArgs = [xLintArg]
+	[compileJava, compileTestJava]*.options*.compilerArgs = [xLintArg, '-parameters']
 
 	task updateCopyrights {
 		onlyIf { !System.getenv('GITHUB_ACTION') && !System.getenv('bamboo_buildKey') }

spring-integration-core/src/main/java/org/springframework/integration/util/ClassUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -235,13 +235,14 @@ public abstract class ClassUtils {
 	}
 
 	/**
-	 * Check if class is Java lambda.
+	 * Check if class is Java or Kotlin lambda.
 	 * @param aClass the {@link Class} to check.
-	 * @return true if class is a Java lambda.
+	 * @return true if class is a Java or Kotlin lambda.
 	 * @since 5.2
 	 */
 	public static boolean isLambda(Class<?> aClass) {
-		return aClass.isSynthetic() && !aClass.isAnonymousClass() && !aClass.isLocalClass();
+		return (aClass.isSynthetic() && !aClass.isAnonymousClass() && !aClass.isLocalClass())
+				|| aClass.getName().contains("$inlined$"); // for Kotlin lambdas
 	}
 
 	/**

spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/KotlinDslTests.kt

@@ -245,7 +245,7 @@ class KotlinDslTests {
 		fun functionFlow() =
 			integrationFlow<Function<ByteArray, String>>({ beanName("functionGateway") }) {
 				transform(Transformers.objectToString()) { id("objectToStringTransformer") }
-				transform<String> { it.toUpperCase() }
+				transform<String> { it.uppercase() }
 				split<Message<*>> { it.payload }
 				split<String>({ it }) { id("splitterEndpoint") }
 				resequence()
@@ -312,7 +312,7 @@ class KotlinDslTests {
 					channel { queue("wireTapChannel") }
 				}
 				delay("delayGroup") { defaultDelay(100) }
-				transform<String> { it.toUpperCase() }
+				transform<String> { it.uppercase() }
 			}
 
 

spring-integration-core/src/test/kotlin/org/springframework/integration/function/FunctionsTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2020 the original author or authors.
+ * Copyright 2018-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -154,7 +154,7 @@ class FunctionsTests {
 		@Bean
 		@Transformer(inputChannel = "functionServiceChannel")
 		fun kotlinFunction(): (String) -> String {
-			return { it.toUpperCase() }
+			return { it.uppercase() }
 		}
 
 		@Bean
@@ -187,7 +187,7 @@ class FunctionsTests {
 		@Bean
 		fun monoFunctionGateway() =
 				integrationFlow<MonoFunction>({ proxyDefaultMethods(true) }) {
-					handle<String>({ p, _ -> Mono.just(p).map(String::toUpperCase) }) { async(true) }
+					handle<String>({ p, _ -> Mono.just(p).map(String::uppercase) }) { async(true) }
 				}
 
 	}

spring-integration-file/src/test/kotlin/org/springframework/integration/kotlin/file/aggregator/KotlinFileAggregatorTests.kt

@@ -42,6 +42,7 @@ import org.springframework.test.context.junit.jupiter.SpringJUnitConfig
 import org.springframework.util.FileCopyUtils
 import java.io.File
 import java.io.FileOutputStream
+import java.util.*
 
 /**
  * @author Artem Bilan
@@ -106,7 +107,7 @@ class KotlinFileAggregatorTests {
 				split(Files.splitter().markers().firstLineAsHeader("firstLine"))
 				channel { executor(taskExecutor) }
 				filter<Any>({ it !is FileMarker }) { discardChannel("aggregatorChannel") }
-				transform(String::toUpperCase)
+				transform(String::uppercase)
 				channel("aggregatorChannel")
 				aggregate(FileAggregator())
 				channel { queue("resultChannel") }

spring-integration-kafka/src/test/kotlin/org/springframework/integration/kafka/dsl/kotlin/KafkaDslKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2020 the original author or authors.
+ * Copyright 2018-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -254,7 +254,7 @@ class KafkaDslKotlinTests {
 								.retryTemplate(RetryTemplate())
 								.filterInRetry(true)) {
 					filter<Message<*>>({ m -> (m.headers[KafkaHeaders.RECEIVED_MESSAGE_KEY] as Int) < 101 }) { throwExceptionOnRejection(true) }
-					transform<String> { it.toUpperCase() }
+					transform<String> { it.uppercase() }
 					channel { queue("listeningFromKafkaResults1") }
 				}
 
@@ -269,7 +269,7 @@ class KafkaDslKotlinTests {
 								.retryTemplate(RetryTemplate())
 								.filterInRetry(true)) {
 					filter<Message<*>>({ m -> (m.headers[KafkaHeaders.RECEIVED_MESSAGE_KEY] as Int) < 101 }) { throwExceptionOnRejection(true) }
-					transform<String> { it.toUpperCase() }
+					transform<String> { it.uppercase() }
 					channel { queue("listeningFromKafkaResults2") }
 				}
 
@@ -355,7 +355,7 @@ class KafkaDslKotlinTests {
 		@Bean
 		fun serverGateway() =
 				integrationFlow(Kafka.inboundGateway(consumerFactory(), containerProperties(), producerFactory())) {
-					transform<String> { it.toUpperCase() }
+					transform<String> { it.uppercase() }
 				}
 
 		private fun containerProperties() =