Annotate generated classes with @generated

This commit annotates every generated class with `@Generated` so that
build tools can recognize and ignore those types if necessary.

Closes spring-projectsgh-29484

spring-beans/src/test/java/org/springframework/beans/factory/aot/BeanDefinitionMethodGeneratorTests.java

@@ -747,7 +747,7 @@ public CodeBlock generateInstanceSupplierCode(GenerationContext generationContex
 	class DeprecationTests {
 
 		private static final TestCompiler TEST_COMPILER = TestCompiler.forSystem()
-				.withCompilerOptions("-Xlint:all", "-Xlint:-rawtypes", "-Werror");
+				.withCompilerOptions("-Xlint:all", "-Xlint:-rawtypes", "-Xlint:-processing", "-Werror");
 
 		@Test
 		void generateBeanDefinitionMethodWithDeprecatedTargetClass() {

spring-beans/src/test/java/org/springframework/beans/factory/aot/CodeWarningsTests.java

@@ -41,7 +41,7 @@
 class CodeWarningsTests {
 
 	private static final TestCompiler TEST_COMPILER = TestCompiler.forSystem()
-			.withCompilerOptions("-Xlint:all", "-Werror");
+			.withCompilerOptions("-Xlint:all", "-Xlint:-processing", "-Werror");
 
 	private final CodeWarnings codeWarnings;
 

spring-beans/src/test/java/org/springframework/beans/factory/aot/InstanceSupplierCodeGeneratorTests.java

@@ -267,7 +267,7 @@ void generateWhenHasStaticFactoryMethodCheckedException() {
 	class DeprecationTests {
 
 		private static final TestCompiler TEST_COMPILER = TestCompiler.forSystem()
-				.withCompilerOptions("-Xlint:all", "-Xlint:-rawtypes", "-Werror");
+				.withCompilerOptions("-Xlint:all", "-Xlint:-rawtypes", "-Xlint:-processing", "-Werror");
 
 		@Test
 		@Disabled("Need to move to a separate method so that the warning can be suppressed")
@@ -323,7 +323,7 @@ private void compileAndCheckWarnings(BeanDefinition beanDefinition) {
 	class DeprecationForRemovalTests {
 
 		private static final TestCompiler TEST_COMPILER = TestCompiler.forSystem()
-				.withCompilerOptions("-Xlint:all", "-Xlint:-rawtypes", "-Werror");
+				.withCompilerOptions("-Xlint:all", "-Xlint:-rawtypes", "-Xlint:-processing", "-Werror");
 
 		@Test
 		@Disabled("Need to move to a separate method so that the warning can be suppressed")

spring-core/src/main/java/org/springframework/aot/generate/Generated.java

@@ -0,0 +1,35 @@
+/*
+ * 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.aot.generate;
+
+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;
+
+/**
+ * Indicate that the type has been generated ahead of time.
+ *
+ * @author Stephane Nicoll
+ * @since 6.1.2
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface Generated {
+}

spring-core/src/main/java/org/springframework/aot/generate/GeneratedClass.java

@@ -142,6 +142,7 @@ JavaFile generateJavaFile() {
 
 	private TypeSpec.Builder apply() {
 		TypeSpec.Builder type = getBuilder(this.type);
+		type.addAnnotation(Generated.class);
 		this.methods.doWithMethodSpecs(type::addMethod);
 		this.declaredClasses.values().forEach(declaredClass ->
 				type.addType(declaredClass.apply().build()));

spring-core/src/test/java/org/springframework/aot/generate/GeneratedClassTests.java

@@ -94,6 +94,14 @@ void getOrAddWhenRepeatReturnsSameGeneratedClass() {
 		assertThat(innerGeneratedClass).isSameAs(innerGeneratedClass2).isSameAs(innerGeneratedClass3);
 	}
 
+	@Test
+	void generateJavaFileIsAnnotatedWithGenerated() {
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
+		assertThat(generatedClass.generateJavaFile().toString())
+				.contains("@Generated")
+				.contains("import " + Generated.class.getName() + ";");
+	}
+
 	@Test
 	void generateJavaFileIncludesGeneratedMethods() {
 		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);