Generate matching structure for configuration classes

This commit improves GeneratedClass to support inner classes, allowing
them to be registered by name with a type customizer, as
GeneratedClasses does for top level classes.

BeanDefinitionMethodGenerator leverages this feature to create a
matching structure for configuration classes that contain inner classes.

Closes gh-29213

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

@@ -44,6 +44,7 @@ import org.springframework.util.StringUtils;
  * Generates a method that returns a {@link BeanDefinition} to be registered.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  * @since 6.0
  * @see BeanDefinitionMethodGeneratorFactory
  */
@@ -97,11 +98,7 @@ class BeanDefinitionMethodGenerator {
 		ClassName target = codeFragments.getTarget(this.registeredBean,
 				this.constructorOrFactoryMethod);
 		if (!target.canonicalName().startsWith("java.")) {
-			GeneratedClass generatedClass = generationContext.getGeneratedClasses()
-					.getOrAddForFeatureComponent("BeanDefinitions", target, type -> {
-						type.addJavadoc("Bean definitions for {@link $T}", target);
-						type.addModifiers(Modifier.PUBLIC);
-					});
+			GeneratedClass generatedClass = lookupGeneratedClass(generationContext, target);
 			GeneratedMethods generatedMethods = generatedClass.getMethods()
 					.withPrefix(getName());
 			GeneratedMethod generatedMethod = generateBeanDefinitionMethod(
@@ -117,6 +114,43 @@ class BeanDefinitionMethodGenerator {
 		return generatedMethod.toMethodReference();
 	}
 
+	/**
+	 * Return the {@link GeneratedClass} to use for the specified {@code target}.
+	 * <p>If the target class is an inner class, a corresponding inner class in
+	 * the original structure is created.
+	 * @param generationContext the generation context to use
+	 * @param target the chosen target class name for the bean definition
+	 * @return the generated class to use
+	 */
+	private static GeneratedClass lookupGeneratedClass(GenerationContext generationContext, ClassName target) {
+		ClassName topLevelClassName = target.topLevelClassName();
+		GeneratedClass generatedClass = generationContext.getGeneratedClasses()
+				.getOrAddForFeatureComponent("BeanDefinitions", topLevelClassName, type -> {
+					type.addJavadoc("Bean definitions for {@link $T}", topLevelClassName);
+					type.addModifiers(Modifier.PUBLIC);
+				});
+		List<String> names = target.simpleNames();
+		if (names.size() == 1) {
+			return generatedClass;
+		}
+		List<String> namesToProcess = names.subList(1, names.size());
+		ClassName currentTargetClassName = topLevelClassName;
+		GeneratedClass tmp = generatedClass;
+		for (String nameToProcess : namesToProcess) {
+			currentTargetClassName = currentTargetClassName.nestedClass(nameToProcess);
+			tmp = createInnerClass(tmp, nameToProcess + "__BeanDefinitions", currentTargetClassName);
+		}
+		return tmp;
+	}
+
+	private static GeneratedClass createInnerClass(GeneratedClass generatedClass,
+			String name, ClassName target) {
+		return generatedClass.getOrAdd(name, type -> {
+			type.addJavadoc("Bean definitions for {@link $T}", target);
+			type.addModifiers(Modifier.PUBLIC, Modifier.STATIC);
+		});
+	}
+
 	private BeanRegistrationCodeFragments getCodeFragments(GenerationContext generationContext,
 			BeanRegistrationsCode beanRegistrationsCode) {
 

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

@@ -42,7 +42,9 @@ import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.beans.testfixture.beans.AnnotatedBean;
 import org.springframework.beans.testfixture.beans.GenericBean;
 import org.springframework.beans.testfixture.beans.TestBean;
+import org.springframework.beans.testfixture.beans.factory.aot.InnerBeanConfiguration;
 import org.springframework.beans.testfixture.beans.factory.aot.MockBeanRegistrationsCode;
+import org.springframework.beans.testfixture.beans.factory.aot.SimpleBean;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.test.io.support.MockSpringFactoriesLoader;
 import org.springframework.core.test.tools.CompileWithForkedClassLoader;
@@ -60,6 +62,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * {@link DefaultBeanRegistrationCodeFragments}.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  */
 class BeanDefinitionMethodGeneratorTests {
 
@@ -99,6 +102,52 @@ class BeanDefinitionMethodGeneratorTests {
 		});
 	}
 
+	@Test
+	void generateBeanDefinitionMethodWhenHasInnerClassTargetMethodGeneratesMethod() {
+		this.beanFactory.registerBeanDefinition("testBeanConfiguration", new RootBeanDefinition(
+				InnerBeanConfiguration.Simple.class));
+		RootBeanDefinition beanDefinition = new RootBeanDefinition(SimpleBean.class);
+		beanDefinition.setFactoryBeanName("testBeanConfiguration");
+		beanDefinition.setFactoryMethodName("simpleBean");
+		RegisteredBean registeredBean = registerBean(beanDefinition);
+		BeanDefinitionMethodGenerator generator = new BeanDefinitionMethodGenerator(
+				this.methodGeneratorFactory, registeredBean, null,
+				Collections.emptyList());
+		MethodReference method = generator.generateBeanDefinitionMethod(
+				this.generationContext, this.beanRegistrationsCode);
+		compile(method, (actual, compiled) -> {
+			SourceFile sourceFile = compiled.getSourceFile(".*BeanDefinitions");
+			assertThat(sourceFile.getClassName()).endsWith("InnerBeanConfiguration__BeanDefinitions");
+			assertThat(sourceFile).contains("public static class Simple__BeanDefinitions")
+					.contains("Bean definitions for {@link InnerBeanConfiguration.Simple}")
+					.doesNotContain("Another__BeanDefinitions");
+
+		});
+	}
+
+	@Test
+	void generateBeanDefinitionMethodWhenHasNestedInnerClassTargetMethodGeneratesMethod() {
+		this.beanFactory.registerBeanDefinition("testBeanConfiguration", new RootBeanDefinition(
+				InnerBeanConfiguration.Simple.Another.class));
+		RootBeanDefinition beanDefinition = new RootBeanDefinition(SimpleBean.class);
+		beanDefinition.setFactoryBeanName("testBeanConfiguration");
+		beanDefinition.setFactoryMethodName("anotherBean");
+		RegisteredBean registeredBean = registerBean(beanDefinition);
+		BeanDefinitionMethodGenerator generator = new BeanDefinitionMethodGenerator(
+				this.methodGeneratorFactory, registeredBean, null,
+				Collections.emptyList());
+		MethodReference method = generator.generateBeanDefinitionMethod(
+				this.generationContext, this.beanRegistrationsCode);
+		compile(method, (actual, compiled) -> {
+			SourceFile sourceFile = compiled.getSourceFile(".*BeanDefinitions");
+			assertThat(sourceFile.getClassName()).endsWith("InnerBeanConfiguration__BeanDefinitions");
+			assertThat(sourceFile).contains("public static class Simple__BeanDefinitions")
+					.contains("Bean definitions for {@link InnerBeanConfiguration.Simple}")
+					.contains("public static class Another__BeanDefinitions")
+					.contains("Bean definitions for {@link InnerBeanConfiguration.Simple.Another}");
+		});
+	}
+
 	@Test
 	void generateBeanDefinitionMethodWhenHasGenericsGeneratesMethod() {
 		RegisteredBean registeredBean = registerBean(new RootBeanDefinition(

spring-beans/src/testFixtures/java/org/springframework/beans/testfixture/beans/factory/aot/InnerBeanConfiguration.java

@@ -0,0 +1,40 @@
+/*
+ * 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.beans.testfixture.beans.factory.aot;
+
+/**
+ * A configuration with inner classes.
+ *
+ * @author Stephane Nicoll
+ */
+public class InnerBeanConfiguration {
+
+	public static class Simple {
+
+		public SimpleBean simpleBean() {
+			return new SimpleBean();
+		}
+
+		public static class Another {
+
+			public SimpleBean anotherBean() {
+				return new SimpleBean();
+			}
+
+		}
+	}
+}

spring-beans/src/testFixtures/java/org/springframework/beans/testfixture/beans/factory/aot/SimpleBeanConfiguration.java

@@ -17,6 +17,7 @@
 package org.springframework.beans.testfixture.beans.factory.aot;
 
 /**
+ * A sample configuration.
  *
  * @author Stephane Nicoll
  */