Add AOT support for Kotlin constructors with optional parameters

This commit leverages Kotlin reflection to instantiate classes
with constructors using optional parameters in the code
generated AOT.

Closes gh-29820

spring-beans/src/main/java/org/springframework/beans/factory/aot/BeanInstanceSupplier.java

@@ -27,6 +27,7 @@ import java.util.stream.Collectors;
 
 import org.springframework.aot.hint.ExecutableMode;
 import org.springframework.beans.BeanInstantiationException;
+import org.springframework.beans.BeanUtils;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.TypeConverter;
 import org.springframework.beans.factory.BeanFactory;
@@ -343,8 +344,7 @@ public final class BeanInstanceSupplier<T> extends AutowiredElementResolver impl
 			Object enclosingInstance = createInstance(declaringClass.getEnclosingClass());
 			args = ObjectUtils.addObjectToArray(args, enclosingInstance, 0);
 		}
-		ReflectionUtils.makeAccessible(constructor);
+		return BeanUtils.instantiateClass(constructor, args);
-		return constructor.newInstance(args);
 	}
 
 	private Object instantiate(ConfigurableBeanFactory beanFactory, Method method, Object[] args) throws Exception {

spring-beans/src/main/java/org/springframework/beans/factory/aot/InstanceSupplierCodeGenerator.java

@@ -24,6 +24,11 @@ import java.lang.reflect.Modifier;
 import java.util.Arrays;
 import java.util.function.Consumer;
 
+import kotlin.jvm.JvmClassMappingKt;
+import kotlin.reflect.KClass;
+import kotlin.reflect.KFunction;
+import kotlin.reflect.KParameter;
+
 import org.springframework.aot.generate.AccessControl;
 import org.springframework.aot.generate.AccessControl.Visibility;
 import org.springframework.aot.generate.GeneratedMethod;
@@ -31,8 +36,11 @@ import org.springframework.aot.generate.GeneratedMethods;
 import org.springframework.aot.generate.GenerationContext;
 import org.springframework.aot.generate.MethodReference.ArgumentCodeGenerator;
 import org.springframework.aot.hint.ExecutableMode;
+import org.springframework.aot.hint.MemberCategory;
+import org.springframework.aot.hint.ReflectionHints;
 import org.springframework.beans.factory.support.InstanceSupplier;
 import org.springframework.beans.factory.support.RegisteredBean;
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.ResolvableType;
 import org.springframework.javapoet.ClassName;
 import org.springframework.javapoet.CodeBlock;
@@ -56,6 +64,7 @@ import org.springframework.util.function.ThrowingSupplier;
  * @author Phillip Webb
  * @author Stephane Nicoll
  * @author Juergen Hoeller
+ * @author Sebastien Deleuze
  * @since 6.0
  */
 class InstanceSupplierCodeGenerator {
@@ -108,11 +117,16 @@ class InstanceSupplierCodeGenerator {
 		boolean dependsOnBean = ClassUtils.isInnerClass(declaringClass);
 
 		Visibility accessVisibility = getAccessVisibility(registeredBean, constructor);
-		if (accessVisibility != Visibility.PRIVATE) {
+		if (KotlinDetector.isKotlinReflectPresent() && KotlinDelegate.hasConstructorWithOptionalParameter(beanClass)) {
+			return generateCodeForInaccessibleConstructor(beanName, beanClass, constructor,
+					dependsOnBean, hints -> hints.registerType(beanClass, MemberCategory.INVOKE_DECLARED_CONSTRUCTORS));
+		}
+		else if (accessVisibility != Visibility.PRIVATE) {
 			return generateCodeForAccessibleConstructor(beanName, beanClass, constructor,
 					dependsOnBean, declaringClass);
 		}
-		return generateCodeForInaccessibleConstructor(beanName, beanClass, constructor, dependsOnBean);
+		return generateCodeForInaccessibleConstructor(beanName, beanClass, constructor, dependsOnBean,
+				hints -> hints.registerConstructor(constructor, ExecutableMode.INVOKE));
 	}
 
 	private CodeBlock generateCodeForAccessibleConstructor(String beanName, Class<?> beanClass,
@@ -137,11 +151,10 @@ class InstanceSupplierCodeGenerator {
 		return generateReturnStatement(generatedMethod);
 	}
 
-	private CodeBlock generateCodeForInaccessibleConstructor(String beanName,
+	private CodeBlock generateCodeForInaccessibleConstructor(String beanName, Class<?> beanClass,
-			Class<?> beanClass, Constructor<?> constructor, boolean dependsOnBean) {
+			Constructor<?> constructor, boolean dependsOnBean, Consumer<ReflectionHints> hints) {
 
-		this.generationContext.getRuntimeHints().reflection()
+		hints.accept(this.generationContext.getRuntimeHints().reflection());
-				.registerConstructor(constructor, ExecutableMode.INVOKE);
 
 		GeneratedMethod generatedMethod = generateGetInstanceSupplierMethod(method -> {
 			method.addJavadoc("Get the bean instance supplier for '$L'.", beanName);
@@ -337,4 +350,25 @@ class InstanceSupplierCodeGenerator {
 				.anyMatch(Exception.class::isAssignableFrom);
 	}
 
+	/**
+	 * Inner class to avoid a hard dependency on Kotlin at runtime.
+	 */
+	private static class KotlinDelegate {
+
+		public static boolean hasConstructorWithOptionalParameter(Class<?> beanClass) {
+			if (KotlinDetector.isKotlinType(beanClass)) {
+				KClass<?> kClass = JvmClassMappingKt.getKotlinClass(beanClass);
+				for (KFunction<?> constructor : kClass.getConstructors()) {
+					for (KParameter parameter : constructor.getParameters()) {
+						if (parameter.isOptional()) {
+							return true;
+						}
+					}
+				}
+			}
+			return false;
+		}
+
+	}
+
 }

spring-beans/src/test/kotlin/org/springframework/beans/factory/aot/InstanceSupplierCodeGeneratorKotlinTests.kt

@@ -0,0 +1,143 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.factory.aot
+
+import org.assertj.core.api.Assertions
+import org.assertj.core.api.ThrowingConsumer
+import org.junit.jupiter.api.Test
+import org.springframework.aot.hint.*
+import org.springframework.aot.test.generate.TestGenerationContext
+import org.springframework.beans.factory.config.BeanDefinition
+import org.springframework.beans.factory.support.DefaultListableBeanFactory
+import org.springframework.beans.factory.support.InstanceSupplier
+import org.springframework.beans.factory.support.RegisteredBean
+import org.springframework.beans.factory.support.RootBeanDefinition
+import org.springframework.beans.testfixture.beans.KotlinTestBean
+import org.springframework.beans.testfixture.beans.KotlinTestBeanWithOptionalParameter
+import org.springframework.beans.testfixture.beans.factory.aot.DeferredTypeBuilder
+import org.springframework.core.test.tools.Compiled
+import org.springframework.core.test.tools.TestCompiler
+import org.springframework.javapoet.MethodSpec
+import org.springframework.javapoet.ParameterizedTypeName
+import org.springframework.javapoet.TypeSpec
+import java.util.function.BiConsumer
+import java.util.function.Supplier
+import javax.lang.model.element.Modifier
+
+/**
+ * Kotlin tests for [InstanceSupplierCodeGenerator].
+ *
+ * @author Sebastien Deleuze
+ */
+class InstanceSupplierCodeGeneratorKotlinTests {
+
+    private val generationContext = TestGenerationContext()
+
+    @Test
+    fun generateWhenHasDefaultConstructor() {
+        val beanDefinition: BeanDefinition = RootBeanDefinition(KotlinTestBean::class.java)
+        val beanFactory = DefaultListableBeanFactory()
+        compile(beanFactory, beanDefinition) { instanceSupplier, compiled ->
+            val bean = getBean<KotlinTestBean>(beanFactory, beanDefinition, instanceSupplier)
+            Assertions.assertThat(bean).isInstanceOf(KotlinTestBean::class.java)
+            Assertions.assertThat(compiled.sourceFile).contains("InstanceSupplier.using(KotlinTestBean::new)")
+        }
+        Assertions.assertThat(getReflectionHints().getTypeHint(KotlinTestBean::class.java))
+            .satisfies(hasConstructorWithMode(ExecutableMode.INTROSPECT))
+    }
+
+    @Test
+    fun generateWhenConstructorHasOptionalParameter() {
+        val beanDefinition: BeanDefinition = RootBeanDefinition(KotlinTestBeanWithOptionalParameter::class.java)
+        val beanFactory = DefaultListableBeanFactory()
+        compile(beanFactory, beanDefinition) { instanceSupplier, compiled ->
+                val bean: KotlinTestBeanWithOptionalParameter = getBean(beanFactory, beanDefinition, instanceSupplier)
+                Assertions.assertThat(bean).isInstanceOf(KotlinTestBeanWithOptionalParameter::class.java)
+                Assertions.assertThat(compiled.sourceFile)
+                    .contains("return BeanInstanceSupplier.<KotlinTestBeanWithOptionalParameter>forConstructor();")
+            }
+        Assertions.assertThat<TypeHint>(getReflectionHints().getTypeHint(KotlinTestBeanWithOptionalParameter::class.java))
+            .satisfies(hasMemberCategory(MemberCategory.INVOKE_DECLARED_CONSTRUCTORS))
+    }
+
+    private fun getReflectionHints(): ReflectionHints {
+        return generationContext.runtimeHints.reflection()
+    }
+
+    private fun hasConstructorWithMode(mode: ExecutableMode): ThrowingConsumer<TypeHint> {
+        return ThrowingConsumer {
+            Assertions.assertThat(it.constructors()).anySatisfy(hasMode(mode))
+        }
+    }
+
+    private fun hasMemberCategory(category: MemberCategory): ThrowingConsumer<TypeHint> {
+        return ThrowingConsumer {
+            Assertions.assertThat(it.memberCategories).contains(category)
+        }
+    }
+
+    private fun hasMode(mode: ExecutableMode): ThrowingConsumer<ExecutableHint> {
+        return ThrowingConsumer {
+            Assertions.assertThat(it.mode).isEqualTo(mode)
+        }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    private fun <T> getBean(beanFactory: DefaultListableBeanFactory, beanDefinition: BeanDefinition,
+                            instanceSupplier: InstanceSupplier<*>): T {
+        (beanDefinition as RootBeanDefinition).instanceSupplier = instanceSupplier
+        beanFactory.registerBeanDefinition("testBean", beanDefinition)
+        return beanFactory.getBean("testBean") as T
+    }
+
+    private fun compile(beanFactory: DefaultListableBeanFactory, beanDefinition: BeanDefinition,
+                        result: BiConsumer<InstanceSupplier<*>, Compiled>) {
+
+        val freshBeanFactory = DefaultListableBeanFactory(beanFactory)
+        freshBeanFactory.registerBeanDefinition("testBean", beanDefinition)
+        val registeredBean = RegisteredBean.of(freshBeanFactory, "testBean")
+        val typeBuilder = DeferredTypeBuilder()
+        val generateClass = generationContext.generatedClasses.addForFeature("TestCode", typeBuilder)
+        val generator = InstanceSupplierCodeGenerator(
+            generationContext, generateClass.name,
+            generateClass.methods, false
+        )
+        val constructorOrFactoryMethod = registeredBean.resolveConstructorOrFactoryMethod()
+        Assertions.assertThat(constructorOrFactoryMethod).isNotNull()
+        val generatedCode = generator.generateCode(registeredBean, constructorOrFactoryMethod)
+        typeBuilder.set { type: TypeSpec.Builder ->
+            type.addModifiers(Modifier.PUBLIC)
+            type.addSuperinterface(
+                ParameterizedTypeName.get(
+                    Supplier::class.java,
+                    InstanceSupplier::class.java
+                )
+            )
+            type.addMethod(
+                MethodSpec.methodBuilder("get")
+                    .addModifiers(Modifier.PUBLIC)
+                    .returns(InstanceSupplier::class.java)
+                    .addStatement("return \$L", generatedCode).build()
+            )
+        }
+        generationContext.writeGeneratedContent()
+        TestCompiler.forSystem().with(generationContext).compile {
+            result.accept(it.getInstance(Supplier::class.java).get() as InstanceSupplier<*>, it)
+        }
+    }
+
+}

spring-beans/src/testFixtures/kotlin/org/springframework/beans/testfixture/beans/KotlinTestBean.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.testfixture.beans
+
+class KotlinTestBean

spring-beans/src/testFixtures/kotlin/org/springframework/beans/testfixture/beans/KotlinTestBeanWithOptionalParameter.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.testfixture.beans
+
+class KotlinTestBeanWithOptionalParameter(private val other: KotlinTestBean = KotlinTestBean())