Add reflection hints for Kotlin reflection on functions

Kotlin reflection API invocation on a specific function
may require iterating on all Java methods to find the right
Kotlin function. As a consequence, this commit adds introspection
hints on the class declared methods for all Kotlin beans since
the impact on the footprint is low.

Closes gh-29663

Author: sdeleuze

spring-context/src/main/java/org/springframework/context/aot/KotlinReflectionBeanRegistrationAotProcessor.java

@@ -0,0 +1,72 @@
+/*
+ * 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.context.aot;
+
+import org.springframework.aot.generate.GenerationContext;
+import org.springframework.aot.hint.MemberCategory;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.beans.factory.aot.BeanRegistrationAotContribution;
+import org.springframework.beans.factory.aot.BeanRegistrationAotProcessor;
+import org.springframework.beans.factory.aot.BeanRegistrationCode;
+import org.springframework.beans.factory.support.RegisteredBean;
+import org.springframework.core.KotlinDetector;
+import org.springframework.lang.Nullable;
+
+/**
+ * AOT {@code BeanRegistrationAotProcessor} that adds additional hints
+ * required by Kotlin reflection.
+ *
+ * @author Sebastien Deleuze
+ * @since 6.0.4
+ */
+class KotlinReflectionBeanRegistrationAotProcessor implements BeanRegistrationAotProcessor {
+
+	@Nullable
+	@Override
+	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
+		Class<?> beanClass = registeredBean.getBeanClass();
+		if (KotlinDetector.isKotlinType(beanClass)) {
+			return new KotlinReflectionBeanRegistrationAotContribution(beanClass);
+		}
+		return null;
+	}
+
+	private static class KotlinReflectionBeanRegistrationAotContribution implements BeanRegistrationAotContribution {
+
+		private final Class<?> beanClass;
+
+		public KotlinReflectionBeanRegistrationAotContribution(Class<?> beanClass) {
+			this.beanClass = beanClass;
+		}
+
+		@Override
+		public void applyTo(GenerationContext generationContext, BeanRegistrationCode beanRegistrationCode) {
+			registerHints(this.beanClass, generationContext.getRuntimeHints());
+		}
+
+		private void registerHints(Class<?> type, RuntimeHints runtimeHints) {
+			if (KotlinDetector.isKotlinType(type)) {
+				runtimeHints.reflection().registerType(type, MemberCategory.INTROSPECT_DECLARED_METHODS);
+			}
+			Class<?> superClass = type.getSuperclass();
+			if (superClass != null) {
+				registerHints(superClass, runtimeHints);
+			}
+		}
+	}
+
+}

spring-context/src/main/resources/META-INF/spring/aot.factories

@@ -1,3 +1,5 @@
 org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor= \
 org.springframework.context.aot.ReflectiveProcessorBeanFactoryInitializationAotProcessor
 
+org.springframework.beans.factory.aot.BeanRegistrationAotProcessor=\
+org.springframework.context.aot.KotlinReflectionBeanRegistrationAotProcessor

spring-context/src/test/java/org/springframework/context/aot/SampleJavaBean.java

@@ -0,0 +1,23 @@
+/*
+ * 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.context.aot;
+
+class SampleJavaBean {
+
+	void sample() {
+	}
+}

spring-context/src/test/kotlin/org/springframework/context/aot/KotlinReflectionBeanRegistrationAotProcessorTests.kt

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2002-2022 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.context.aot
+
+import org.assertj.core.api.Assertions
+import org.junit.jupiter.api.Test
+import org.mockito.Mockito
+import org.springframework.aot.generate.GenerationContext
+import org.springframework.aot.hint.MemberCategory
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates
+import org.springframework.aot.test.generate.TestGenerationContext
+import org.springframework.beans.factory.aot.*
+import org.springframework.beans.factory.support.DefaultListableBeanFactory
+import org.springframework.beans.factory.support.RegisteredBean
+import org.springframework.beans.factory.support.RootBeanDefinition
+
+/**
+ * Tests for [KotlinReflectionBeanRegistrationAotProcessor].
+ *
+ * @author Sebastien Deleuze
+ */
+class KotlinReflectionBeanRegistrationAotProcessorTests {
+
+	private val processor = KotlinReflectionBeanRegistrationAotProcessor()
+
+	private val generationContext = TestGenerationContext()
+
+	@Test
+	fun processorIsRegistered() {
+		Assertions.assertThat(
+			AotServices.factories(javaClass.classLoader).load(BeanRegistrationAotProcessor::class.java))
+			.anyMatch(KotlinReflectionBeanRegistrationAotProcessor::class.java::isInstance)
+	}
+
+	@Test
+	fun shouldProcessKotlinBean() {
+		process(SampleKotlinBean::class.java)
+		Assertions.assertThat(
+			RuntimeHintsPredicates.reflection()
+				.onType(SampleKotlinBean::class.java)
+				.withMemberCategory(MemberCategory.INTROSPECT_DECLARED_METHODS)
+		).accepts(generationContext.runtimeHints)
+		Assertions.assertThat(
+			RuntimeHintsPredicates.reflection()
+				.onType(BaseKotlinBean::class.java)
+				.withMemberCategory(MemberCategory.INTROSPECT_DECLARED_METHODS)
+		).accepts(generationContext.runtimeHints)
+	}
+
+	@Test
+	fun shouldNotProcessJavaBean() {
+		process(SampleJavaBean::class.java)
+		Assertions.assertThat(generationContext.runtimeHints.reflection().typeHints()).isEmpty()
+	}
+
+	private fun process(beanClass: Class<*>) {
+		createContribution(beanClass)?.applyTo(generationContext, Mockito.mock(BeanRegistrationCode::class.java))
+	}
+
+	private fun createContribution(beanClass: Class<*>): BeanRegistrationAotContribution? {
+		val beanFactory = DefaultListableBeanFactory()
+		beanFactory.registerBeanDefinition(beanClass.name, RootBeanDefinition(beanClass))
+		return processor.processAheadOfTime(RegisteredBean.of(beanFactory, beanClass.name))
+	}
+
+
+	class SampleKotlinBean : BaseKotlinBean() {
+		fun sample() {
+		}
+	}
+
+	open class BaseKotlinBean {
+		fun base() {
+		}
+	}
+
+}