Allow MergedBeanDefinitionPostProcessor to handle bean creation

This commit registers the MergedBeanDefinitionPostProcessor instances
on the BeanFactory processed for AOT purposes. This allows beans that
are created at build-time to be post-processed for low-level needs such
as initialization and autowiring.

Closes gh-28777

Author: snicoll

spring-context/src/main/java/org/springframework/context/support/PostProcessorRegistrationDelegate.java

@@ -364,7 +364,7 @@ private static void invokeBeanFactoryPostProcessors(
 	 * Register the given BeanPostProcessor beans.
 	 */
 	private static void registerBeanPostProcessors(
-			ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
+			ConfigurableListableBeanFactory beanFactory, List<? extends BeanPostProcessor> postProcessors) {
 
 		if (beanFactory instanceof AbstractBeanFactory) {
 			// Bulk addition is more efficient against our CopyOnWriteArrayList there
@@ -439,6 +439,7 @@ private void invokeMergedBeanDefinitionPostProcessors() {
 				Class<?> beanType = resolveBeanType(bd);
 				postProcessRootBeanDefinition(postProcessors, beanName, beanType, bd);
 			}
+			registerBeanPostProcessors(this.beanFactory, postProcessors);
 		}
 
 		private void postProcessRootBeanDefinition(List<MergedBeanDefinitionPostProcessor> postProcessors,

spring-context/src/test/java/org/springframework/context/annotation/AnnotationConfigApplicationContextTests.java

@@ -431,6 +431,24 @@ void refreshForAotProcessingWithConfiguration() {
 				"annotationConfigApplicationContextTests.Config", "testBean");
 	}
 
+	@Test
+	void refreshForAotCanInstantiateBeanWithAutowiredApplicationContext() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		context.register(BeanD.class);
+		context.refreshForAotProcessing();
+		BeanD bean = context.getBean(BeanD.class);
+		assertThat(bean.applicationContext).isSameAs(context);
+	}
+
+	@Test
+	void refreshForAotCanInstantiateBeanWithFieldAutowiredApplicationContext() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		context.register(BeanB.class);
+		context.refreshForAotProcessing();
+		BeanB bean = context.getBean(BeanB.class);
+		assertThat(bean.applicationContext).isSameAs(context);
+	}
+
 
 	@Configuration
 	static class Config {
@@ -506,6 +524,16 @@ public BeanB() {
 
 	static class BeanC {}
 
+	static class BeanD {
+
+		private final ApplicationContext applicationContext;
+
+		public BeanD(ApplicationContext applicationContext) {
+			this.applicationContext = applicationContext;
+		}
+
+	}
+
 	static class NonInstantiatedFactoryBean implements FactoryBean<String> {
 
 		NonInstantiatedFactoryBean() {

spring-context/src/test/java/org/springframework/context/support/GenericApplicationContextTests.java

@@ -23,10 +23,12 @@
 import org.junit.jupiter.api.condition.OS;
 import org.mockito.ArgumentCaptor;
 
+import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
 import org.springframework.beans.factory.config.AbstractFactoryBean;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
+import org.springframework.beans.factory.support.AbstractBeanDefinition;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.support.GenericBeanDefinition;
 import org.springframework.beans.factory.support.MergedBeanDefinitionPostProcessor;
@@ -407,6 +409,32 @@ void refreshForAotInvokesMergedBeanDefinitionPostProcessorsOnPropertyValue() {
 		context.close();
 	}
 
+	@Test
+	void refreshForAotInvokesBeanPostProcessorContractOnMergedBeanDefinitionPostProcessors() {
+		MergedBeanDefinitionPostProcessor bpp = new MergedBeanDefinitionPostProcessor() {
+			@Override
+			public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
+				beanDefinition.setAttribute("mbdppCalled", true);
+			}
+
+			@Override
+			public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
+				return (beanName.equals("test") ? "42" : bean);
+			}
+		};
+		GenericApplicationContext context = new GenericApplicationContext();
+		context.registerBeanDefinition("bpp", BeanDefinitionBuilder.rootBeanDefinition(
+						MergedBeanDefinitionPostProcessor.class, () -> bpp)
+				.setRole(BeanDefinition.ROLE_INFRASTRUCTURE).getBeanDefinition());
+		AbstractBeanDefinition bd = BeanDefinitionBuilder.rootBeanDefinition(String.class)
+				.addConstructorArgValue("value").getBeanDefinition();
+		context.registerBeanDefinition("test", bd);
+		context.refreshForAotProcessing();
+		assertThat(context.getBeanFactory().getMergedBeanDefinition("test")
+				.hasAttribute("mbdppCalled")).isTrue();
+		assertThat(context.getBean("test")).isEqualTo("42");
+	}
+
 	@Test
 	void refreshForAotFailsOnAnActiveContext() {
 		GenericApplicationContext context = new GenericApplicationContext();