Explicit error message for bean name clash with containing configuration class

Issue: SPR-15775

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

@@ -198,6 +198,11 @@ class ConfigurationClassBeanDefinitionReader {
 
 		// Has this effectively been overridden before (e.g. via XML)?
 		if (isOverriddenByExistingDefinition(beanMethod, beanName)) {
+			if (beanName.equals(beanMethod.getConfigurationClass().getBeanName())) {
+				throw new BeanDefinitionStoreException(beanMethod.getConfigurationClass().getResource().getDescription(),
+						beanName, "Bean name derived from @Bean method '" + beanMethod.getMetadata().getMethodName() +
+						"' clashes with bean name for containing configuration class; please make those names unique!");
+			}
 			return;
 		}