Ignore DefaultConstructorMarker in BeanUtils#getParameterNames

Closes gh-34760

Author: sdeleuze

spring-beans/src/main/java/org/springframework/beans/BeanUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -33,6 +33,7 @@
 import java.util.Set;
 
 import kotlin.jvm.JvmClassMappingKt;
+import kotlin.jvm.internal.DefaultConstructorMarker;
 import kotlin.reflect.KClass;
 import kotlin.reflect.KFunction;
 import kotlin.reflect.KParameter;
@@ -669,7 +670,9 @@ public static String[] getParameterNames(Constructor<?> ctor) {
 		ConstructorProperties cp = ctor.getAnnotation(ConstructorProperties.class);
 		String[] paramNames = (cp != null ? cp.value() : parameterNameDiscoverer.getParameterNames(ctor));
 		Assert.state(paramNames != null, () -> "Cannot resolve parameter names for constructor " + ctor);
-		Assert.state(paramNames.length == ctor.getParameterCount(),
+		int parameterCount = (KotlinDetector.isKotlinReflectPresent() && KotlinDelegate.hasDefaultConstructorMarker(ctor) ?
+				ctor.getParameterCount() - 1 : ctor.getParameterCount());
+		Assert.state(paramNames.length == parameterCount,
 				() -> "Invalid number of parameter names: " + paramNames.length + " for constructor " + ctor);
 		return paramNames;
 	}
@@ -939,6 +942,11 @@ public static <T> T instantiateClass(Constructor<T> ctor, Object... args)
 			}
 			return kotlinConstructor.callBy(argParameters);
 		}
+
+		public static boolean hasDefaultConstructorMarker(Constructor<?> ctor) {
+			int parameterCount = ctor.getParameterCount();
+			return parameterCount > 0 && ctor.getParameters()[parameterCount -1].getType() == DefaultConstructorMarker.class;
+		}
 	}
 
 }

spring-beans/src/test/kotlin/org/springframework/beans/BeanUtilsKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -157,6 +157,48 @@ class BeanUtilsKotlinTests {
 		assertThat(instance).isEqualTo(ConstructorWithNullablePrimitiveValueClass(null))
 	}
 
+	@Test
+	fun `Get parameter names with Foo`() {
+		val ctor = BeanUtils.findPrimaryConstructor(Foo::class.java)!!
+		val names = BeanUtils.getParameterNames(ctor)
+		assertThat(names).containsExactly("param1", "param2")
+	}
+
+	@Test
+	fun `Get parameter names filters out DefaultConstructorMarker with ConstructorWithValueClass`() {
+		val ctor = BeanUtils.findPrimaryConstructor(ConstructorWithValueClass::class.java)!!
+		val names = BeanUtils.getParameterNames(ctor)
+		assertThat(names).containsExactly("value")
+	}
+
+	@Test
+	fun `getParameterNames filters out DefaultConstructorMarker with ConstructorWithNullableValueClass`() {
+		val ctor = BeanUtils.findPrimaryConstructor(ConstructorWithNullableValueClass::class.java)!!
+		val names = BeanUtils.getParameterNames(ctor)
+		assertThat(names).containsExactly("value")
+	}
+
+	@Test
+	fun `getParameterNames filters out DefaultConstructorMarker with ConstructorWithPrimitiveValueClass`() {
+		val ctor = BeanUtils.findPrimaryConstructor(ConstructorWithPrimitiveValueClass::class.java)!!
+		val names = BeanUtils.getParameterNames(ctor)
+		assertThat(names).containsExactly("value")
+	}
+
+	@Test
+	fun `getParameterNames filters out DefaultConstructorMarker with ConstructorWithNullablePrimitiveValueClass`() {
+		val ctor = BeanUtils.findPrimaryConstructor(ConstructorWithNullablePrimitiveValueClass::class.java)!!
+		val names = BeanUtils.getParameterNames(ctor)
+		assertThat(names).containsExactly("value")
+	}
+
+	@Test
+	fun `getParameterNames with ClassWithZeroParameterCtor`() {
+		val ctor = BeanUtils.findPrimaryConstructor(ClassWithZeroParameterCtor::class.java)!!
+		val names = BeanUtils.getParameterNames(ctor)
+		assertThat(names).isEmpty()
+	}
+
 
 	class Foo(val param1: String, val param2: Int)
 
@@ -216,4 +258,6 @@ class BeanUtilsKotlinTests {
 
 	data class ConstructorWithNullablePrimitiveValueClass(val value: PrimitiveValueClass?)
 
+	class ClassWithZeroParameterCtor()
+
 }