Support load-time weaving for @component classes again

Since Spring Framework 5.2, the LoadTimeWeaver no longer weaves bean
classes annotated with @component. This is a regression caused by the
changes in 40c6213, stemming from the fact that any class annotated
or meta-annotated with @component is considered to be a candidate
configuration class in 'configuration lite' mode (i.e., a class without
the @configuration annotation and without any @bean methods) and
therefore now has its class eagerly loaded. This results in the class
being loaded before the LoadTimeWeaver has a chance to weave it.

This commit fixes this regression by explicitly avoiding eager class
loading for any 'lite' @configuration or @component class without @bean
methods.

Closes spring-projectsgh-26199

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

@@ -81,6 +81,7 @@
  * @author Chris Beams
  * @author Juergen Hoeller
  * @author Phillip Webb
+ * @author Sam Brannen
  * @since 3.0
  */
 public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
@@ -376,21 +377,30 @@ public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFact
 		for (String beanName : beanFactory.getBeanDefinitionNames()) {
 			BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
 			Object configClassAttr = beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE);
+			AnnotationMetadata annotationMetadata = null;
 			MethodMetadata methodMetadata = null;
 			if (beanDef instanceof AnnotatedBeanDefinition) {
-				methodMetadata = ((AnnotatedBeanDefinition) beanDef).getFactoryMethodMetadata();
+				AnnotatedBeanDefinition annotatedBeanDefinition = (AnnotatedBeanDefinition) beanDef;
+				annotationMetadata = annotatedBeanDefinition.getMetadata();
+				methodMetadata = annotatedBeanDefinition.getFactoryMethodMetadata();
 			}
 			if ((configClassAttr != null || methodMetadata != null) && beanDef instanceof AbstractBeanDefinition) {
 				// Configuration class (full or lite) or a configuration-derived @Bean method
-				// -> resolve bean class at this point...
+				// -> eagerly resolve bean class at this point, unless it's a 'lite' configuration
+				// or component class without @Bean methods.
 				AbstractBeanDefinition abd = (AbstractBeanDefinition) beanDef;
 				if (!abd.hasBeanClass()) {
-					try {
-						abd.resolveBeanClass(this.beanClassLoader);
-					}
-					catch (Throwable ex) {
-						throw new IllegalStateException(
-								"Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
+					boolean liteConfigurationCandidateWithoutBeanMethods =
+							(ConfigurationClassUtils.CONFIGURATION_CLASS_LITE.equals(configClassAttr) &&
+								annotationMetadata != null && !ConfigurationClassUtils.hasBeanMethods(annotationMetadata));
+					if (!liteConfigurationCandidateWithoutBeanMethods) {
+						try {
+							abd.resolveBeanClass(this.beanClassLoader);
+						}
+						catch (Throwable ex) {
+							throw new IllegalStateException(
+									"Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
+						}
 					}
 				}
 			}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -46,6 +46,7 @@
  *
  * @author Chris Beams
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 3.1
  */
 abstract class ConfigurationClassUtils {
@@ -162,6 +163,10 @@ public static boolean isConfigurationCandidate(AnnotationMetadata metadata) {
 		}
 
 		// Finally, let's look for @Bean methods...
+		return hasBeanMethods(metadata);
+	}
+
+	static boolean hasBeanMethods(AnnotationMetadata metadata) {
 		try {
 			return metadata.hasAnnotatedMethods(Bean.class.getName());
 		}