GH-3740: Fix HandlerAdapter to detect Kotlin suspend functions

spring-kafka/src/main/java/org/springframework/kafka/listener/adapter/HandlerAdapter.java

@@ -16,8 +16,11 @@
 
 package org.springframework.kafka.listener.adapter;
 
+import java.lang.reflect.Method;
+
 import org.jspecify.annotations.Nullable;
 
+import org.springframework.core.KotlinDetector;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.handler.invocation.InvocableHandlerMethod;
 
@@ -27,6 +30,7 @@
  * underlying handler.
  *
  * @author Gary Russell
+ * @author Artem Bilan
  *
  */
 public class HandlerAdapter {
@@ -44,7 +48,10 @@ public class HandlerAdapter {
 	public HandlerAdapter(InvocableHandlerMethod invokerHandlerMethod) {
 		this.invokerHandlerMethod = invokerHandlerMethod;
 		this.delegatingHandler = null;
-		this.asyncReplies = AdapterUtils.isAsyncReply(invokerHandlerMethod.getMethod().getReturnType());
+		Method handlerMethod = invokerHandlerMethod.getMethod();
+		this.asyncReplies =
+				AdapterUtils.isAsyncReply(handlerMethod.getReturnType())
+						|| KotlinDetector.isSuspendingFunction(handlerMethod);
 	}
 
 	/**

spring-kafka/src/test/kotlin/org/springframework/kafka/listener/EnableKafkaKotlinCoroutinesTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 the original author or authors.
+ * Copyright 2016-2025 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.
@@ -20,6 +20,7 @@ import org.apache.kafka.clients.producer.ProducerConfig
 import org.apache.kafka.common.serialization.StringDeserializer
 import org.apache.kafka.common.serialization.StringSerializer
 import org.assertj.core.api.Assertions.assertThat
+import org.awaitility.Awaitility.await
 import org.junit.jupiter.api.Test
 import org.springframework.beans.factory.annotation.Autowired
 import org.springframework.beans.factory.annotation.Value
@@ -29,10 +30,16 @@ import org.springframework.kafka.annotation.EnableKafka
 import org.springframework.kafka.annotation.KafkaHandler
 import org.springframework.kafka.annotation.KafkaListener
 import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory
-import org.springframework.kafka.core.*
+import org.springframework.kafka.core.ConsumerFactory
+import org.springframework.kafka.core.DefaultKafkaConsumerFactory
+import org.springframework.kafka.core.DefaultKafkaProducerFactory
+import org.springframework.kafka.core.KafkaTemplate
+import org.springframework.kafka.core.ProducerFactory
 import org.springframework.kafka.listener.KafkaListenerErrorHandler
+import org.springframework.kafka.support.Acknowledgment
 import org.springframework.kafka.test.EmbeddedKafkaBroker
 import org.springframework.kafka.test.context.EmbeddedKafka
+import org.springframework.kafka.test.utils.KafkaTestUtils
 import org.springframework.messaging.handler.annotation.SendTo
 import org.springframework.test.annotation.DirtiesContext
 import org.springframework.test.context.junit.jupiter.SpringJUnitConfig
@@ -45,6 +52,7 @@ import java.util.concurrent.TimeUnit
  * Kotlin Annotated async return listener tests.
  *
  * @author Wang ZhiYang
+ * @author Artem Bilan
  *
  * @since 3.1
  */
@@ -65,6 +73,11 @@ class EnableKafkaKotlinCoroutinesTests {
 		this.template.send("kotlinAsyncTestTopic1", "foo")
 		assertThat(this.config.latch1.await(10, TimeUnit.SECONDS)).isTrue()
 		assertThat(this.config.received).isEqualTo("foo")
+		await()
+			.untilAsserted {
+				assertThat(KafkaTestUtils.getPropertyValue(this.config.acknowledgment, "acked"))
+					.isEqualTo(java.lang.Boolean.TRUE)
+			}
 	}
 
 	@Test
@@ -114,6 +127,8 @@ class EnableKafkaKotlinCoroutinesTests {
 		@Volatile
 		lateinit var received: String
 
+		lateinit var acknowledgment: Acknowledgment
+
 		@Volatile
 		lateinit var batchReceived: String
 
@@ -204,8 +219,9 @@ class EnableKafkaKotlinCoroutinesTests {
 
 		@KafkaListener(id = "kotlin", topics = ["kotlinAsyncTestTopic1"],
 				containerFactory = "kafkaListenerContainerFactory")
-		suspend fun listen(value: String) {
+		suspend fun listen(value: String, acknowledgment: Acknowledgment) {
 			this.received = value
+			this.acknowledgment = acknowledgment
 			this.latch1.countDown()
 		}