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
  */

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

@@ -24,6 +24,7 @@ import java.util.function.Consumer;
 import org.springframework.javapoet.ClassName;
 import org.springframework.javapoet.JavaFile;
 import org.springframework.javapoet.TypeSpec;
+import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**
@@ -36,13 +37,18 @@ import org.springframework.util.Assert;
  */
 public final class GeneratedClass {
 
+	@Nullable
+	private final GeneratedClass enclosingClass;
+
 	private final ClassName name;
 
 	private final GeneratedMethods methods;
 
 	private final Consumer<TypeSpec.Builder> type;
 
-	private final Map<MethodName, AtomicInteger> methodNameSequenceGenerator = new ConcurrentHashMap<>();
+	private final Map<ClassName, GeneratedClass> declaredClasses;
+
+	private final Map<MethodName, AtomicInteger> methodNameSequenceGenerator;
 
 
 	/**
@@ -53,9 +59,17 @@ public final class GeneratedClass {
 	 * @param type a {@link Consumer} used to build the type
 	 */
 	GeneratedClass(ClassName name, Consumer<TypeSpec.Builder> type) {
+		this(null, name, type);
+	}
+
+	private GeneratedClass(@Nullable GeneratedClass enclosingClass, ClassName name,
+			Consumer<TypeSpec.Builder> type) {
+		this.enclosingClass = enclosingClass;
 		this.name = name;
 		this.type = type;
 		this.methods = new GeneratedMethods(name, this::generateSequencedMethodName);
+		this.declaredClasses = new ConcurrentHashMap<>();
+		this.methodNameSequenceGenerator = new ConcurrentHashMap<>();
 	}
 
 
@@ -79,6 +93,16 @@ public final class GeneratedClass {
 		return (sequence > 0) ? name.toString() + sequence : name.toString();
 	}
 
+	/**
+	 * Return the enclosing {@link GeneratedClass} or {@code null} if this
+	 * instance represents a top-level class.
+	 * @return the enclosing generated class, if any
+	 */
+	@Nullable
+	public GeneratedClass getEnclosingClass() {
+		return this.enclosingClass;
+	}
+
 	/**
 	 * Return the name of the generated class.
 	 * @return the name of the generated class
@@ -95,10 +119,33 @@ public final class GeneratedClass {
 		return this.methods;
 	}
 
+	/**
+	 * Get or add a nested generated class with the specified name. If this method
+	 * has previously been called with the given {@code name}, the existing class
+	 * will be returned, otherwise a new class will be generated.
+	 * @param name the name of the nested class
+	 * @param type a {@link Consumer} used to build the type
+	 * @return an existing or newly generated class whose enclosing class is this class
+	 */
+	public GeneratedClass getOrAdd(String name, Consumer<TypeSpec.Builder> type) {
+		ClassName className = this.name.nestedClass(name);
+		return this.declaredClasses.computeIfAbsent(className,
+				key -> new GeneratedClass(this, className, type));
+	}
+
 	JavaFile generateJavaFile() {
+		Assert.state(getEnclosingClass() == null,
+				"Java file cannot be generated for an inner class");
+		TypeSpec.Builder type = apply();
+		return JavaFile.builder(this.name.packageName(), type.build()).build();
+	}
+
+	private TypeSpec.Builder apply() {
 		TypeSpec.Builder type = getBuilder(this.type);
 		this.methods.doWithMethodSpecs(type::addMethod);
-		return JavaFile.builder(this.name.packageName(), type.build()).build();
+		this.declaredClasses.values().forEach(declaredClass ->
+				type.addType(declaredClass.apply().build()));
+		return type;
 	}
 
 	private TypeSpec.Builder getBuilder(Consumer<TypeSpec.Builder> type) {

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

@@ -18,6 +18,8 @@ package org.springframework.aot.generate;
 
 import java.util.function.Consumer;
 
+import javax.lang.model.element.Modifier;
+
 import org.junit.jupiter.api.Test;
 
 import org.springframework.javapoet.ClassName;
@@ -35,21 +37,34 @@ import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
  */
 class GeneratedClassTests {
 
+	private static final ClassName TEST_CLASS_NAME = ClassName.get("com.example", "Test");
+
 	private static final Consumer<TypeSpec.Builder> emptyTypeCustomizer = type -> {};
 
 	private static final Consumer<MethodSpec.Builder> emptyMethodCustomizer = method -> {};
 
+	@Test
+	void getEnclosingNameOnTopLevelClassReturnsNull() {
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
+		assertThat(generatedClass.getEnclosingClass()).isNull();
+	}
+
+	@Test
+	void getEnclosingNameOnInnerClassReturnsParent() {
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
+		GeneratedClass innerGeneratedClass = generatedClass.getOrAdd("Test", emptyTypeCustomizer);
+		assertThat(innerGeneratedClass.getEnclosingClass()).isEqualTo(generatedClass);
+	}
+
 	@Test
 	void getNameReturnsName() {
-		ClassName name = ClassName.bestGuess("com.example.Test");
-		GeneratedClass generatedClass = new GeneratedClass(name, emptyTypeCustomizer);
-		assertThat(generatedClass.getName()).isSameAs(name);
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
+		assertThat(generatedClass.getName()).isSameAs(TEST_CLASS_NAME);
 	}
 
 	@Test
 	void reserveMethodNamesWhenNameUsedThrowsException() {
-		ClassName name = ClassName.bestGuess("com.example.Test");
-		GeneratedClass generatedClass = new GeneratedClass(name, emptyTypeCustomizer);
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
 		generatedClass.getMethods().add("apply", emptyMethodCustomizer);
 		assertThatIllegalStateException()
 				.isThrownBy(() -> generatedClass.reserveMethodNames("apply"));
@@ -57,8 +72,7 @@ class GeneratedClassTests {
 
 	@Test
 	void reserveMethodNamesReservesNames() {
-		ClassName name = ClassName.bestGuess("com.example.Test");
-		GeneratedClass generatedClass = new GeneratedClass(name, emptyTypeCustomizer);
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
 		generatedClass.reserveMethodNames("apply");
 		GeneratedMethod generatedMethod = generatedClass.getMethods().add("apply", emptyMethodCustomizer);
 		assertThat(generatedMethod.getName()).isEqualTo("apply1");
@@ -66,18 +80,45 @@ class GeneratedClassTests {
 
 	@Test
 	void generateMethodNameWhenAllEmptyPartsGeneratesSetName() {
-		ClassName name = ClassName.bestGuess("com.example.Test");
-		GeneratedClass generatedClass = new GeneratedClass(name, emptyTypeCustomizer);
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
 		GeneratedMethod generatedMethod = generatedClass.getMethods().add("123", emptyMethodCustomizer);
 		assertThat(generatedMethod.getName()).isEqualTo("$$aot");
 	}
 
+	@Test
+	void getOrAddWhenRepeatReturnsSameGeneratedClass() {
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
+		GeneratedClass innerGeneratedClass = generatedClass.getOrAdd("Inner", emptyTypeCustomizer);
+		GeneratedClass innerGeneratedClass2 = generatedClass.getOrAdd("Inner", emptyTypeCustomizer);
+		GeneratedClass innerGeneratedClass3 = generatedClass.getOrAdd("Inner", emptyTypeCustomizer);
+		assertThat(innerGeneratedClass).isSameAs(innerGeneratedClass2).isSameAs(innerGeneratedClass3);
+	}
+
 	@Test
 	void generateJavaFileIncludesGeneratedMethods() {
-		ClassName name = ClassName.bestGuess("com.example.Test");
-		GeneratedClass generatedClass = new GeneratedClass(name, emptyTypeCustomizer);
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
 		generatedClass.getMethods().add("test", method -> method.addJavadoc("Test Method"));
 		assertThat(generatedClass.generateJavaFile().toString()).contains("Test Method");
 	}
 
+	@Test
+	void generateJavaFileIncludesDeclaredClasses() {
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME);
+		generatedClass.getOrAdd("First", type -> type.modifiers.add(Modifier.STATIC));
+		generatedClass.getOrAdd("Second", type -> type.modifiers.add(Modifier.PRIVATE));
+		assertThat(generatedClass.generateJavaFile().toString())
+				.contains("static class First").contains("private class Second");
+	}
+
+	@Test
+	void generateJavaFileOnInnerClassThrowsException() {
+		GeneratedClass generatedClass = createGeneratedClass(TEST_CLASS_NAME)
+				.getOrAdd("Inner", emptyTypeCustomizer);
+		assertThatIllegalStateException().isThrownBy(generatedClass::generateJavaFile);
+	}
+
+	private static GeneratedClass createGeneratedClass(ClassName className) {
+		return new GeneratedClass(className, emptyTypeCustomizer);
+	}
+
 }