Support Kotlin value classes as suspending function arguments

Similar to gh-31698 but for Coroutines.

See gh-31846

spring-core/src/main/java/org/springframework/core/CoroutinesUtils.java

@@ -18,6 +18,7 @@ package org.springframework.core;
 
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
 import java.util.Map;
 import java.util.Objects;
 
@@ -40,6 +41,7 @@ import kotlinx.coroutines.flow.Flow;
 import kotlinx.coroutines.reactor.MonoKt;
 import kotlinx.coroutines.reactor.ReactorFlowKt;
 import org.reactivestreams.Publisher;
+import org.springframework.util.ReflectionUtils;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -55,6 +57,9 @@ import org.springframework.util.CollectionUtils;
  */
 public abstract class CoroutinesUtils {
 
+	private static final ReflectionUtils.MethodFilter boxImplFilter =
+			(method -> method.isSynthetic() && Modifier.isStatic(method.getModifiers()) && method.getName().equals("box-impl"));
+
 	/**
 	 * Convert a {@link Deferred} instance to a {@link Mono}.
 	 */
@@ -115,7 +120,14 @@ public abstract class CoroutinesUtils {
 							case INSTANCE -> argMap.put(parameter, target);
 							case VALUE -> {
 								if (!parameter.isOptional() || args[index] != null) {
-									argMap.put(parameter, args[index]);
+									if (parameter.getType().getClassifier() instanceof KClass<?> kClass && kClass.isValue()) {
+										Class<?> javaClass = JvmClassMappingKt.getJavaClass(kClass);
+										Method[] methods = ReflectionUtils.getUniqueDeclaredMethods(javaClass, boxImplFilter);
+										Assert.state(methods.length == 1, "Unable to find a single box-impl synthetic static method in " + javaClass.getName());
+										argMap.put(parameter, ReflectionUtils.invokeMethod(methods[0], null, args[index]));
+									} else {
+										argMap.put(parameter, args[index]);
+									}
 								}
 								index++;
 							}

spring-core/src/test/kotlin/org/springframework/core/CoroutinesUtilsTests.kt

@@ -145,6 +145,15 @@ class CoroutinesUtilsTests {
 		}
 	}
 
+	@Test
+	fun invokeSuspendingFunctionWithValueClassParameter() {
+		val method = CoroutinesUtilsTests::class.java.declaredMethods.first { it.name.startsWith("suspendingFunctionWithValueClass") }
+		val mono = CoroutinesUtils.invokeSuspendingFunction(method, this, "foo", null) as Mono
+		runBlocking {
+			Assertions.assertThat(mono.awaitSingle()).isEqualTo("foo")
+		}
+	}
+
 	suspend fun suspendingFunction(value: String): String {
 		delay(1)
 		return value
@@ -172,4 +181,12 @@ class CoroutinesUtilsTests {
 		return null
 	}
 
+	suspend fun suspendingFunctionWithValueClass(value: ValueClass): String {
+		delay(1)
+		return value.value
+	}
+
+	@JvmInline
+	value class ValueClass(val value: String)
+
 }