Add support of declarative use of reflection

This commit adds a `@Reflective` annotation that can be used to declare
that the annotated element requires reflection at runtime. By default,
the annotated element is exposed but this can be customized by
specifying a dedicated `ReflectiveProcessor`.

Closes gh-28469

spring-core/src/main/java/org/springframework/aot/hint/annotation/Reflective.java

@@ -0,0 +1,57 @@
+/*
+ * 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.aot.hint.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.core.annotation.AliasFor;
+
+/**
+ * Indicate that the annotated element requires reflection.
+ *
+ * <p>When present, either directly or as a meta-annotation, this annotation
+ * triggers the configured {@linkplain ReflectiveProcessor processors} against
+ * the annotated element. By default, a reflection hint is added on the
+ * annotated element so that it can be discovered and invoked if necessary.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ * @see SimpleReflectiveProcessor
+ */
+@Target({ ElementType.ANNOTATION_TYPE, ElementType.TYPE, ElementType.CONSTRUCTOR,
+		ElementType.FIELD, ElementType.METHOD })
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface Reflective {
+
+	/**
+	 * Alias for {@link #processors()}.
+	 */
+	Class<? extends ReflectiveProcessor>[] value() default SimpleReflectiveProcessor.class;
+
+	/**
+	 * {@link ReflectiveProcessor} implementations to invoke against the
+	 * annotated element.
+	 */
+	@AliasFor("value")
+	Class<? extends ReflectiveProcessor>[] processors() default SimpleReflectiveProcessor.class;
+
+}

spring-core/src/main/java/org/springframework/aot/hint/annotation/ReflectiveProcessor.java

@@ -0,0 +1,39 @@
+/*
+ * 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.aot.hint.annotation;
+
+import java.lang.reflect.AnnotatedElement;
+
+import org.springframework.aot.hint.ReflectionHints;
+
+/**
+ * Process an {@link AnnotatedElement} and register the necessary reflection
+ * hints for it.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ */
+public interface ReflectiveProcessor {
+
+	/**
+	 * Register {@link ReflectionHints} against the specified {@link AnnotatedElement}.
+	 * @param hints the reflection hints instance to use
+	 * @param element the element to process
+	 */
+	void registerReflectionHints(ReflectionHints hints, AnnotatedElement element);
+
+}

spring-core/src/main/java/org/springframework/aot/hint/annotation/SimpleReflectiveProcessor.java

@@ -0,0 +1,93 @@
+/*
+ * 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.aot.hint.annotation;
+
+import java.lang.reflect.AnnotatedElement;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.util.function.Consumer;
+
+import org.springframework.aot.hint.ExecutableHint.Builder;
+import org.springframework.aot.hint.ExecutableMode;
+import org.springframework.aot.hint.ReflectionHints;
+
+/**
+ * A simple {@link ReflectiveProcessor} implementation that registers only a
+ * reflection hint for the annotated type. Can be sub-classed to customize
+ * processing for a given {@link AnnotatedElement} type.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ */
+public class SimpleReflectiveProcessor implements ReflectiveProcessor {
+
+	private static final Consumer<Builder> INVOKE_EXECUTABLE = hint -> hint.setModes(ExecutableMode.INVOKE);
+
+	@Override
+	public void registerReflectionHints(ReflectionHints hints, AnnotatedElement element) {
+		if (element instanceof Class<?> type) {
+			registerTypeHint(hints, type);
+		}
+		else if (element instanceof Constructor<?> constructor) {
+			registerConstructorHint(hints, constructor);
+		}
+		else if (element instanceof Field field) {
+			registerFieldHint(hints, field);
+		}
+		else if (element instanceof Method method) {
+			registerMethodHint(hints, method);
+		}
+	}
+
+	/**
+	 * Register {@link ReflectionHints} against the specified {@link Class}.
+	 * @param hints the reflection hints instance to use
+	 * @param type the class to process
+	 */
+	protected void registerTypeHint(ReflectionHints hints, Class<?> type) {
+		hints.registerType(type, hint -> {});
+	}
+
+	/**
+	 * Register {@link ReflectionHints} against the specified {@link Constructor}.
+	 * @param hints the reflection hints instance to use
+	 * @param constructor the constructor to process
+	 */
+	protected void registerConstructorHint(ReflectionHints hints, Constructor<?> constructor) {
+		hints.registerConstructor(constructor, INVOKE_EXECUTABLE);
+	}
+
+	/**
+	 * Register {@link ReflectionHints} against the specified {@link Field}.
+	 * @param hints the reflection hints instance to use
+	 * @param field the field to process
+	 */
+	protected void registerFieldHint(ReflectionHints hints, Field field) {
+		hints.registerField(field);
+	}
+
+	/**
+	 * Register {@link ReflectionHints} against the specified {@link Method}.
+	 * @param hints the reflection hints instance to use
+	 * @param method the method to process
+	 */
+	protected void registerMethodHint(ReflectionHints hints, Method method) {
+		hints.registerMethod(method, INVOKE_EXECUTABLE);
+	}
+
+}

spring-core/src/main/java/org/springframework/aot/hint/annotation/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * Annotation support for runtime hints.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.aot.hint.annotation;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;

spring-core/src/test/java/org/springframework/aot/hint/annotation/SimpleReflectiveProcessorTests.java

@@ -0,0 +1,115 @@
+/*
+ * 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.aot.hint.annotation;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aot.hint.ExecutableMode;
+import org.springframework.aot.hint.ReflectionHints;
+import org.springframework.aot.hint.TypeReference;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link SimpleReflectiveProcessor}.
+ *
+ * @author Stephane Nicoll
+ */
+class SimpleReflectiveProcessorTests {
+
+	private final SimpleReflectiveProcessor processor = new SimpleReflectiveProcessor();
+
+	private final ReflectionHints hints = new ReflectionHints();
+
+	@Test
+	void registerReflectiveHintsForClass() {
+		processor.registerReflectionHints(hints, SampleBean.class);
+		assertThat(hints.typeHints()).singleElement().satisfies(typeHint -> {
+			assertThat(typeHint.getType()).isEqualTo(TypeReference.of(SampleBean.class));
+			assertThat(typeHint.getMemberCategories()).isEmpty();
+			assertThat(typeHint.constructors()).isEmpty();
+			assertThat(typeHint.fields()).isEmpty();
+			assertThat(typeHint.methods()).isEmpty();
+		});
+	}
+
+	@Test
+	void registerReflectiveHintsForConstructor() {
+		Constructor<?> constructor = SampleBean.class.getDeclaredConstructors()[0];
+		processor.registerReflectionHints(hints, constructor);
+		assertThat(hints.typeHints()).singleElement().satisfies(typeHint -> {
+			assertThat(typeHint.getType()).isEqualTo(TypeReference.of(SampleBean.class));
+			assertThat(typeHint.getMemberCategories()).isEmpty();
+			assertThat(typeHint.constructors()).singleElement().satisfies(constructorHint -> {
+				assertThat(constructorHint.getName()).isEqualTo("<init>");
+				assertThat(constructorHint.getModes()).containsExactly(ExecutableMode.INVOKE);
+				assertThat(constructorHint.getParameterTypes()).containsExactly(TypeReference.of(String.class));
+			});
+			assertThat(typeHint.fields()).isEmpty();
+			assertThat(typeHint.methods()).isEmpty();
+		});
+	}
+
+	@Test
+	void registerReflectiveHintsForField() throws NoSuchFieldException {
+		Field field = SampleBean.class.getDeclaredField("name");
+		processor.registerReflectionHints(hints, field);
+		assertThat(hints.typeHints()).singleElement().satisfies(typeHint -> {
+			assertThat(typeHint.getType()).isEqualTo(TypeReference.of(SampleBean.class));
+			assertThat(typeHint.getMemberCategories()).isEmpty();
+			assertThat(typeHint.constructors()).isEmpty();
+			assertThat(typeHint.fields()).singleElement().satisfies(fieldHint ->
+					assertThat(fieldHint.getName()).isEqualTo("name"));
+			assertThat(typeHint.methods()).isEmpty();
+		});
+	}
+
+	@Test
+	void registerReflectiveHintsForMethod() throws NoSuchMethodException {
+		Method method = SampleBean.class.getDeclaredMethod("setName", String.class);
+		processor.registerReflectionHints(hints, method);
+		assertThat(hints.typeHints()).singleElement().satisfies(typeHint -> {
+			assertThat(typeHint.getType()).isEqualTo(TypeReference.of(SampleBean.class));
+			assertThat(typeHint.getMemberCategories()).isEmpty();
+			assertThat(typeHint.constructors()).isEmpty();
+			assertThat(typeHint.fields()).isEmpty();
+			assertThat(typeHint.methods()).singleElement().satisfies(methodHint -> {
+				assertThat(methodHint.getName()).isEqualTo("setName");
+				assertThat(methodHint.getModes()).containsExactly(ExecutableMode.INVOKE);
+				assertThat(methodHint.getParameterTypes()).containsExactly(TypeReference.of(String.class));
+			});
+		});
+	}
+
+	static class SampleBean {
+
+		private String name;
+
+		SampleBean(String name) {
+			this.name = name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+	}
+
+}