Log warn message with specific guidance in BeanPostProcessorChecker

Closes gh-24092

Author: jhoeller

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * 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.
@@ -20,6 +20,7 @@
 import java.util.Collection;
 import java.util.Comparator;
 import java.util.HashSet;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.function.BiConsumer;
@@ -227,7 +228,8 @@ public static void registerBeanPostProcessors(
 		// a bean is created during BeanPostProcessor instantiation, i.e. when
 		// a bean is not eligible for getting processed by all BeanPostProcessors.
 		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
-		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
+		beanFactory.addBeanPostProcessor(
+				new BeanPostProcessorChecker(beanFactory, postProcessorNames, beanProcessorTargetCount));
 
 		// Separate between BeanPostProcessors that implement PriorityOrdered,
 		// Ordered, and the rest.
@@ -389,10 +391,15 @@ private static final class BeanPostProcessorChecker implements BeanPostProcessor
 
 		private final ConfigurableListableBeanFactory beanFactory;
 
+		private final String[] postProcessorNames;
+
 		private final int beanPostProcessorTargetCount;
 
-		public BeanPostProcessorChecker(ConfigurableListableBeanFactory beanFactory, int beanPostProcessorTargetCount) {
+		public BeanPostProcessorChecker(ConfigurableListableBeanFactory beanFactory,
+				String[] postProcessorNames, int beanPostProcessorTargetCount) {
+
 			this.beanFactory = beanFactory;
+			this.postProcessorNames = postProcessorNames;
 			this.beanPostProcessorTargetCount = beanPostProcessorTargetCount;
 		}
 
@@ -405,10 +412,30 @@ public Object postProcessBeforeInitialization(Object bean, String beanName) {
 		public Object postProcessAfterInitialization(Object bean, String beanName) {
 			if (!(bean instanceof BeanPostProcessor) && !isInfrastructureBean(beanName) &&
 					this.beanFactory.getBeanPostProcessorCount() < this.beanPostProcessorTargetCount) {
-				if (logger.isInfoEnabled()) {
-					logger.info("Bean '" + beanName + "' of type [" + bean.getClass().getName() +
+				if (logger.isWarnEnabled()) {
+					Set<String> bppsInCreation = new LinkedHashSet<>(2);
+					for (String bppName : this.postProcessorNames) {
+						if (this.beanFactory.isCurrentlyInCreation(bppName)) {
+							bppsInCreation.add(bppName);
+						}
+					}
+					if (bppsInCreation.size() == 1) {
+						String bppName = bppsInCreation.iterator().next();
+						if (this.beanFactory.containsBeanDefinition(bppName) &&
+								beanName.equals(this.beanFactory.getBeanDefinition(bppName).getFactoryBeanName())) {
+							logger.warn("Bean '" + beanName + "' of type [" + bean.getClass().getName() +
+									"] is not eligible for getting processed by all BeanPostProcessors " +
+									"(for example: not eligible for auto-proxying). The currently created " +
+									"BeanPostProcessor " + bppsInCreation + " is declared through a non-static " +
+									"factory method on that class; consider declaring it as static instead.");
+							return bean;
+						}
+					}
+					logger.warn("Bean '" + beanName + "' of type [" + bean.getClass().getName() +
 							"] is not eligible for getting processed by all BeanPostProcessors " +
-							"(for example: not eligible for auto-proxying)");
+							"(for example: not eligible for auto-proxying). Is this bean getting eagerly " +
+							"injected into a currently created BeanPostProcessor " + bppsInCreation + "? " +
+							"Check the corresponding BeanPostProcessor declaration and its dependencies.");
 				}
 			}
 			return bean;