Enable cglib proxy for configuration classes if necessary

This commit updates code generation to customize the instantiation of
a configuration class that requires a proxy. Rather than instantiating
the raw class, the proxy is used.

Closes gh-29107

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassEnhancer.java

@@ -73,7 +73,7 @@ import org.springframework.util.ReflectionUtils;
 class ConfigurationClassEnhancer {
 
 	// The callbacks to use. Note that these callbacks must be stateless.
-	private static final Callback[] CALLBACKS = new Callback[] {
+	static final Callback[] CALLBACKS = new Callback[] {
 			new BeanMethodInterceptor(),
 			new BeanFactoryAwareMethodInterceptor(),
 			NoOp.INSTANCE

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassPostProcessor.java

@@ -18,6 +18,8 @@ package org.springframework.context.annotation;
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Executable;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -26,6 +28,7 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Predicate;
 import java.util.function.Supplier;
 
 import javax.lang.model.element.Modifier;
@@ -46,6 +49,11 @@ import org.springframework.beans.factory.annotation.AnnotatedBeanDefinition;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotContribution;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor;
 import org.springframework.beans.factory.aot.BeanFactoryInitializationCode;
+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.aot.BeanRegistrationCodeFragments;
+import org.springframework.beans.factory.aot.BeanRegistrationCodeFragmentsDecorator;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
@@ -61,6 +69,7 @@ import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
 import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.beans.factory.support.RegisteredBean;
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.ApplicationStartupAware;
 import org.springframework.context.EnvironmentAware;
@@ -110,8 +119,8 @@ import org.springframework.util.CollectionUtils;
  * @since 3.0
  */
 public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
-		BeanFactoryInitializationAotProcessor, PriorityOrdered, ResourceLoaderAware, ApplicationStartupAware,
-		BeanClassLoaderAware, EnvironmentAware {
+		BeanRegistrationAotProcessor, BeanFactoryInitializationAotProcessor, PriorityOrdered,
+		ResourceLoaderAware, ApplicationStartupAware, BeanClassLoaderAware, EnvironmentAware {
 
 	/**
 	 * A {@code BeanNameGenerator} using fully qualified class names as default bean names.
@@ -294,6 +303,19 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 		beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
 	}
 
+	@Nullable
+	@Override
+	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
+		Object configClassAttr = registeredBean.getMergedBeanDefinition()
+				.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE);
+		if (ConfigurationClassUtils.CONFIGURATION_CLASS_FULL.equals(configClassAttr)) {
+			Class<?> proxyClass = registeredBean.getBeanType().toClass();
+			return BeanRegistrationAotContribution.withCustomCodeFragments(codeFragments ->
+					new ConfigurationClassProxyBeanRegistrationCodeFragments(codeFragments, proxyClass));
+		}
+		return null;
+	}
+
 	@Override
 	public BeanFactoryInitializationAotContribution processAheadOfTime(ConfigurableListableBeanFactory beanFactory) {
 		boolean hasPropertySourceDescriptors = !CollectionUtils.isEmpty(this.propertySourceDescriptors);
@@ -692,4 +714,47 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 
 	}
 
+	private static class ConfigurationClassProxyBeanRegistrationCodeFragments extends BeanRegistrationCodeFragmentsDecorator {
+
+		private final Class<?> proxyClass;
+
+		public ConfigurationClassProxyBeanRegistrationCodeFragments(BeanRegistrationCodeFragments codeFragments,
+				Class<?> proxyClass) {
+			super(codeFragments);
+			this.proxyClass = proxyClass;
+		}
+
+		@Override
+		public CodeBlock generateSetBeanDefinitionPropertiesCode(GenerationContext generationContext,
+				BeanRegistrationCode beanRegistrationCode, RootBeanDefinition beanDefinition, Predicate<String> attributeFilter) {
+			CodeBlock.Builder code = CodeBlock.builder();
+			code.add(super.generateSetBeanDefinitionPropertiesCode(generationContext,
+					beanRegistrationCode, beanDefinition, attributeFilter));
+			code.addStatement("$T.initializeConfigurationClass($T.class)",
+					ConfigurationClassUtils.class, ClassUtils.getUserClass(this.proxyClass));
+			return code.build();
+		}
+
+		@Override
+		public CodeBlock generateInstanceSupplierCode(GenerationContext generationContext,
+				BeanRegistrationCode beanRegistrationCode, Executable constructorOrFactoryMethod,
+				boolean allowDirectSupplierShortcut) {
+			return super.generateInstanceSupplierCode(generationContext, beanRegistrationCode,
+					proxyExecutable(constructorOrFactoryMethod), allowDirectSupplierShortcut);
+		}
+
+		private Executable proxyExecutable(Executable rawClassExecutable) {
+			if (rawClassExecutable instanceof Constructor<?>) {
+				try {
+					return this.proxyClass.getConstructor(rawClassExecutable.getParameterTypes());
+				}
+				catch (NoSuchMethodException ex) {
+					throw new IllegalStateException("No matching constructor found on proxy " + this.proxyClass, ex);
+				}
+			}
+			return rawClassExecutable;
+		}
+
+	}
+
 }

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * 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.
@@ -30,6 +30,7 @@ import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.beans.factory.support.AbstractBeanDefinition;
+import org.springframework.cglib.proxy.Enhancer;
 import org.springframework.context.event.EventListenerFactory;
 import org.springframework.core.Conventions;
 import org.springframework.core.Ordered;
@@ -42,23 +43,24 @@ import org.springframework.lang.Nullable;
 import org.springframework.stereotype.Component;
 
 /**
- * Utilities for identifying {@link Configuration} classes.
+ * Utilities for identifying and configuring {@link Configuration} classes.
  *
  * @author Chris Beams
  * @author Juergen Hoeller
  * @author Sam Brannen
- * @since 3.1
+ * @author Stephane Nicoll
+ * @since 6.0
  */
-abstract class ConfigurationClassUtils {
+public abstract class ConfigurationClassUtils {
 
-	public static final String CONFIGURATION_CLASS_FULL = "full";
+	static final String CONFIGURATION_CLASS_FULL = "full";
 
-	public static final String CONFIGURATION_CLASS_LITE = "lite";
+	static final String CONFIGURATION_CLASS_LITE = "lite";
 
-	public static final String CONFIGURATION_CLASS_ATTRIBUTE =
+	static final String CONFIGURATION_CLASS_ATTRIBUTE =
 			Conventions.getQualifiedAttributeName(ConfigurationClassPostProcessor.class, "configurationClass");
 
-	private static final String ORDER_ATTRIBUTE =
+	static final String ORDER_ATTRIBUTE =
 			Conventions.getQualifiedAttributeName(ConfigurationClassPostProcessor.class, "order");
 
 
@@ -73,6 +75,17 @@ abstract class ConfigurationClassUtils {
 		candidateIndicators.add(ImportResource.class.getName());
 	}
 
+	/**
+	 * Initialize a configuration class proxy for the specified class.
+	 * @param userClass the configuration class to initialize
+	 */
+	@SuppressWarnings("unused") // Used by AOT-optimized generated code
+	public static Class<?> initializeConfigurationClass(Class<?> userClass) {
+		Class<?> configurationClass = new ConfigurationClassEnhancer().enhance(userClass, null);
+		Enhancer.registerStaticCallbacks(configurationClass, ConfigurationClassEnhancer.CALLBACKS);
+		return configurationClass;
+	}
+
 
 	/**
 	 * Check whether the given bean definition is a candidate for a configuration class
@@ -82,7 +95,7 @@ abstract class ConfigurationClassUtils {
 	 * @param metadataReaderFactory the current factory in use by the caller
 	 * @return whether the candidate qualifies as (any kind of) configuration class
 	 */
-	public static boolean checkConfigurationClassCandidate(
+	static boolean checkConfigurationClassCandidate(
 			BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {
 
 		String className = beanDef.getBeanClassName();
@@ -149,7 +162,7 @@ abstract class ConfigurationClassUtils {
 	 * @return {@code true} if the given class is to be registered for
 	 * configuration class processing; {@code false} otherwise
 	 */
-	public static boolean isConfigurationCandidate(AnnotationMetadata metadata) {
+	static boolean isConfigurationCandidate(AnnotationMetadata metadata) {
 		// Do not consider an interface or an annotation...
 		if (metadata.isInterface()) {
 			return false;