Treat directly registered class as configuration 'lite' mode candidate

Prior to this commit, if a non-annotated [1] class was registered
directly with an ApplicationContext -- for example, via
AnnotatedBeanDefinitionReader, AnnotationConfigApplicationContext, or
@ContextConfiguration -- it was not considered a configuration class in
'lite' mode unless @Bean methods were declared locally. In other words,
if the registered class didn't declare local @Bean methods but rather
extended a class that declared @Bean methods, then the registered class
was not parsed as a @Configuration class in 'lite' mode, and the @Bean
methods were ignored.

Whereas, a non-annotated class registered via @Import is always
considered to be a configuration class candidate.

To address this discrepancy between @Import'ed classes and classes
registered directly with an ApplicationContext, this commit treats any
class registered via AnnotatedBeanDefinitionReader as a @Configuration
class candidate with @Bean 'lite' mode semantics.

[1] In this context, "non-annotated" means a class not annotated (or
meta-annotated) with @Component, @ComponentScan, @Import, or
@ImportResource.

Closes gh-30449

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

@@ -255,6 +255,7 @@ public class AnnotatedBeanDefinitionReader {
 			return;
 		}
 
+		abd.setAttribute(ConfigurationClassUtils.CANDIDATE_ATTRIBUTE, Boolean.TRUE);
 		abd.setInstanceSupplier(supplier);
 		ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
 		abd.setScope(scopeMetadata.getScopeName());

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

@@ -56,6 +56,17 @@ public abstract class ConfigurationClassUtils {
 
 	static final String CONFIGURATION_CLASS_LITE = "lite";
 
+	/**
+	 * When set to {@link Boolean#TRUE}, this attribute signals that the bean class
+	 * for the given {@link BeanDefinition} should be considered as a candidate
+	 * configuration class in 'lite' mode by default.
+	 * <p>For example, a class registered directly with an {@code ApplicationContext}
+	 * should always be considered a configuration class candidate.
+	 * @since 6.0.10
+	 */
+	static final String CANDIDATE_ATTRIBUTE =
+			Conventions.getQualifiedAttributeName(ConfigurationClassPostProcessor.class, "candidate");
+
 	static final String CONFIGURATION_CLASS_ATTRIBUTE =
 			Conventions.getQualifiedAttributeName(ConfigurationClassPostProcessor.class, "configurationClass");
 
@@ -136,7 +147,8 @@ public abstract class ConfigurationClassUtils {
 		if (config != null && !Boolean.FALSE.equals(config.get("proxyBeanMethods"))) {
 			beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
 		}
-		else if (config != null || isConfigurationCandidate(metadata)) {
+		else if (config != null || Boolean.TRUE.equals(beanDef.getAttribute(CANDIDATE_ATTRIBUTE)) ||
+				isConfigurationCandidate(metadata)) {
 			beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
 		}
 		else {

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

@@ -0,0 +1,109 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.context.annotation;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link Bean @Bean} 'lite' mode features that are not covered
+ * elsewhere in the test suite.
+ *
+ * @author Sam Brannen
+ * @since 6.0.10
+ * @see ConfigurationClassPostProcessorTests
+ */
+class BeanLiteModeTests {
+
+	@Test
+	void beanMethodsAreFoundWhenInheritedAsInterfaceDefaultMethods() {
+		assertBeansAreFound(InterfaceDefaultMethodsConfig.class);
+	}
+
+	@Test
+	void beanMethodsAreFoundWhenDeclaredLocally() {
+		assertBeansAreFound(BaseConfig.class);
+	}
+
+	@Test
+	void beanMethodsAreFoundWhenDeclaredLocallyAndInSuperclass() {
+		assertBeansAreFound(OverridingConfig.class, "foo", "xyz");
+	}
+
+	@Test  // gh-30449
+	void beanMethodsAreFoundWhenDeclaredOnlyInSuperclass() {
+		assertBeansAreFound(ExtendedConfig.class, "foo", "xyz");
+	}
+
+	private static void assertBeansAreFound(Class<?> configClass) {
+		assertBeansAreFound(configClass, "foo", "bar");
+	}
+
+	private static void assertBeansAreFound(Class<?> configClass, String expected1, String expected2) {
+		try (AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(configClass)) {
+			String bean1 = context.getBean("bean1", String.class);
+			String bean2 = context.getBean("bean2", String.class);
+
+			assertThat(bean1).isEqualTo(expected1);
+			assertThat(bean2).isEqualTo(expected2);
+		}
+	}
+
+
+	interface ConfigInterface {
+
+		@Bean
+		default String bean1() {
+			return "foo";
+		}
+
+		@Bean
+		default String bean2() {
+			return "bar";
+		}
+	}
+
+	static class InterfaceDefaultMethodsConfig implements ConfigInterface {
+	}
+
+	static class BaseConfig {
+
+		@Bean
+		String bean1() {
+			return "foo";
+		}
+
+		@Bean
+		String bean2() {
+			return "bar";
+		}
+	}
+
+	static class OverridingConfig extends BaseConfig {
+
+		@Bean
+		@Override
+		String bean2() {
+			return "xyz";
+		}
+	}
+
+	static class ExtendedConfig extends OverridingConfig {
+	}
+
+}