Fix Kotlin inner class nested configuration handling

Before this commit, Kotlin inner class nested configuration
handling thrown an IndexOutOfBoundsException due to bogus filtering
of its constructor parameter reference to an instance of the outer
class.

This commit keep constructor parameter of type INSTANCE in order to
throw a more meaningful NoSuchBeanDefinitionException.

Issue: SPR-17222

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

@@ -29,6 +29,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
 import kotlin.reflect.KFunction;
@@ -768,17 +769,21 @@ public class MethodParameter {
 			}
 			else {
 				KFunction<?> function = null;
+				Predicate<KParameter> predicate = null;
 				if (method != null) {
 					function = ReflectJvmMapping.getKotlinFunction(method);
+					predicate = p -> KParameter.Kind.VALUE.equals(p.getKind());
 				}
 				else if (ctor != null) {
 					function = ReflectJvmMapping.getKotlinFunction(ctor);
+					predicate = p -> KParameter.Kind.VALUE.equals(p.getKind()) ||
+							KParameter.Kind.INSTANCE.equals(p.getKind());
 				}
 				if (function != null) {
 					List<KParameter> parameters = function.getParameters();
 					KParameter parameter = parameters
 							.stream()
-							.filter(p -> KParameter.Kind.VALUE.equals(p.getKind()))
+							.filter(predicate)
 							.collect(Collectors.toList())
 							.get(index);
 					return (parameter.getType().isMarkedNullable() || parameter.isOptional());

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -13,15 +13,11 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.core
 
-import java.lang.reflect.Method
-
-import org.junit.Before
 import org.junit.Test
-
 import org.junit.Assert.*
+import java.lang.reflect.Method
 
 /**
  * Tests for Kotlin support in [MethodParameter].
@@ -32,36 +28,58 @@ import org.junit.Assert.*
  */
 class KotlinMethodParameterTests {
 
-	lateinit var nullableMethod: Method
+	private val nullableMethod: Method = javaClass.getMethod("nullable", String::class.java)
 
-	lateinit var nonNullableMethod: Method
+	private val nonNullableMethod = javaClass.getMethod("nonNullable", String::class.java)
 
+	private val innerClassConstructor = InnerClass::class.java.getConstructor(KotlinMethodParameterTests::class.java)
 
-	@Before
-	@Throws(NoSuchMethodException::class)
-	fun setup() {
-		nullableMethod = javaClass.getMethod("nullable", String::class.java)
-		nonNullableMethod = javaClass.getMethod("nonNullable", String::class.java)
-	}
+	private val innerClassWithParametersConstructor = InnerClassWithParameter::class.java
+			.getConstructor(KotlinMethodParameterTests::class.java, String::class.java, String::class.java)
+
+	private val regularClassConstructor = RegularClass::class.java.getConstructor(String::class.java, String::class.java)
 
 
 	@Test
 	fun `Method parameter nullability`() {
-		assertTrue(MethodParameter(nullableMethod, 0).isOptional())
-		assertFalse(MethodParameter(nonNullableMethod, 0).isOptional())
+		assertTrue(MethodParameter(nullableMethod, 0).isOptional)
+		assertFalse(MethodParameter(nonNullableMethod, 0).isOptional)
 	}
 
 	@Test
 	fun `Method return type nullability`() {
-		assertTrue(MethodParameter(nullableMethod, -1).isOptional())
-		assertFalse(MethodParameter(nonNullableMethod, -1).isOptional())
+		assertTrue(MethodParameter(nullableMethod, -1).isOptional)
+		assertFalse(MethodParameter(nonNullableMethod, -1).isOptional)
+	}
+
+	@Test  // SPR-17222
+	fun `Inner class constructor`() {
+		assertFalse(MethodParameter(innerClassConstructor, 0).isOptional)
+
+		assertFalse(MethodParameter(innerClassWithParametersConstructor, 0).isOptional)
+		assertFalse(MethodParameter(innerClassWithParametersConstructor, 1).isOptional)
+		assertTrue(MethodParameter(innerClassWithParametersConstructor, 2).isOptional)
+	}
+
+	@Test
+	fun `Regular class constructor`() {
+		assertFalse(MethodParameter(regularClassConstructor, 0).isOptional)
+		assertTrue(MethodParameter(regularClassConstructor, 1).isOptional)
 	}
 
 
-	@Suppress("unused", "unused_parameter")
-	fun nullable(p1: String?): Int? = 42
+	@Suppress("unused_parameter")
+	fun nullable(nullable: String?): Int? = 42
 
-	@Suppress("unused", "unused_parameter")
-	fun nonNullable(p1: String): Int = 42
+	@Suppress("unused_parameter")
+	fun nonNullable(nonNullable: String): Int = 42
+
+	inner class InnerClass
+
+	@Suppress("unused_parameter")
+	inner class InnerClassWithParameter(nonNullable: String, nullable: String?)
+
+	@Suppress("unused_parameter")
+	class RegularClass(nonNullable: String, nullable: String?)
 
 }

src/docs/asciidoc/languages/kotlin.adoc

@@ -143,6 +143,10 @@ for serializing / deserializing JSON data is automatically registered when
 found in the classpath and a warning message will be logged if Jackson and Kotlin are
 detected without the Jackson Kotlin module present.
 
+Configuration classes can be
+https://kotlinlang.org/docs/reference/nested-classes.html[top level or nested but not inner]
+since the later requires a reference to the outer class.
+