Proper exception in case of an @Bean method call encountering a bean type mismatch

Issue: SPR-12905

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

@@ -27,6 +27,8 @@ import org.springframework.aop.scope.ScopedProxyFactoryBean;
 import org.springframework.asm.Type;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
+import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
 import org.springframework.beans.factory.config.ConfigurableBeanFactory;
 import org.springframework.beans.factory.support.SimpleInstantiationStrategy;
@@ -303,7 +305,7 @@ class ConfigurationClassEnhancer {
 							"result in a failure to process annotations such as @Autowired, " +
 							"@Resource and @PostConstruct within the method's declaring " +
 							"@Configuration class. Add the 'static' modifier to this method to avoid " +
-							"these container lifecycle issues; see @Bean javadoc for complete details",
+							"these container lifecycle issues; see @Bean javadoc for complete details.",
 							beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName()));
 				}
 				return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);
@@ -318,8 +320,23 @@ class ConfigurationClassEnhancer {
 					if (alreadyInCreation) {
 						beanFactory.setCurrentlyInCreation(beanName, false);
 					}
-					return (!ObjectUtils.isEmpty(beanMethodArgs) ?
+					Object beanInstance = (!ObjectUtils.isEmpty(beanMethodArgs) ?
 							beanFactory.getBean(beanName, beanMethodArgs) : beanFactory.getBean(beanName));
+					if (beanInstance != null && !beanMethod.getReturnType().isInstance(beanInstance)) {
+						String msg = String.format("@Bean method %s.%s called as a bean reference " +
+									"for type [%s] but overridden by non-compatible bean instance of type [%s].",
+									beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
+									beanMethod.getReturnType().getName(), beanInstance.getClass().getName());
+						try {
+							BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName);
+							msg += " Overriding bean of same name declared in: " + beanDefinition.getResourceDescription();
+						}
+						catch (NoSuchBeanDefinitionException ex) {
+							// Ignore - simply no detailed message then.
+						}
+						throw new IllegalStateException(msg);
+					}
+					return beanInstance;
 				}
 				finally {
 					if (alreadyInCreation) {

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

@@ -298,8 +298,45 @@ public class ConfigurationClassPostProcessorTests {
 		beanFactory.registerBeanDefinition("config2", new RootBeanDefinition(SingletonBeanConfig.class));
 		ConfigurationClassPostProcessor pp = new ConfigurationClassPostProcessor();
 		pp.postProcessBeanFactory(beanFactory);
-		assertTrue(beanFactory.getBean(Foo.class) instanceof ExtendedFoo);
-		beanFactory.getBean(Bar.class);
+
+		Foo foo = beanFactory.getBean(Foo.class);
+		assertTrue(foo instanceof ExtendedFoo);
+		Bar bar = beanFactory.getBean(Bar.class);
+		assertSame(foo, bar.foo);
+	}
+
+	@Test
+	public void configurationClassesWithValidOverridingForProgrammaticCall() {
+		beanFactory.registerBeanDefinition("config1", new RootBeanDefinition(OverridingAgainSingletonBeanConfig.class));
+		beanFactory.registerBeanDefinition("config2", new RootBeanDefinition(OverridingSingletonBeanConfig.class));
+		beanFactory.registerBeanDefinition("config3", new RootBeanDefinition(SingletonBeanConfig.class));
+		ConfigurationClassPostProcessor pp = new ConfigurationClassPostProcessor();
+		pp.postProcessBeanFactory(beanFactory);
+
+		Foo foo = beanFactory.getBean(Foo.class);
+		assertTrue(foo instanceof ExtendedAgainFoo);
+		Bar bar = beanFactory.getBean(Bar.class);
+		assertSame(foo, bar.foo);
+	}
+
+	@Test
+	public void configurationClassesWithInvalidOverridingForProgrammaticCall() {
+		beanFactory.registerBeanDefinition("config1", new RootBeanDefinition(InvalidOverridingSingletonBeanConfig.class));
+		beanFactory.registerBeanDefinition("config2", new RootBeanDefinition(OverridingSingletonBeanConfig.class));
+		beanFactory.registerBeanDefinition("config3", new RootBeanDefinition(SingletonBeanConfig.class));
+		ConfigurationClassPostProcessor pp = new ConfigurationClassPostProcessor();
+		pp.postProcessBeanFactory(beanFactory);
+
+		try {
+			beanFactory.getBean(Bar.class);
+			fail("Should have thrown BeanCreationException");
+		}
+		catch (BeanCreationException ex) {
+			assertTrue(ex.getMessage().contains("OverridingSingletonBeanConfig.foo"));
+			assertTrue(ex.getMessage().contains(ExtendedFoo.class.getName()));
+			assertTrue(ex.getMessage().contains(Foo.class.getName()));
+			assertTrue(ex.getMessage().contains("InvalidOverridingSingletonBeanConfig"));
+		}
 	}
 
 	@Test
@@ -311,6 +348,7 @@ public class ConfigurationClassPostProcessorTests {
 		beanFactory.registerBeanDefinition("consumer", new RootBeanDefinition(ScopedProxyConsumer.class));
 		ConfigurationClassPostProcessor pp = new ConfigurationClassPostProcessor();
 		pp.postProcessBeanFactory(beanFactory);
+
 		ITestBean injected = beanFactory.getBean("consumer", ScopedProxyConsumer.class).testBean;
 		assertTrue(injected instanceof ScopedObject);
 		assertSame(beanFactory.getBean("scopedClass"), injected);
@@ -549,13 +587,11 @@ public class ConfigurationClassPostProcessorTests {
 	@Order(1)
 	static class SingletonBeanConfig {
 
-		public @Bean
-		Foo foo() {
+		public @Bean Foo foo() {
 			return new Foo();
 		}
 
-		public @Bean
-		Bar bar() {
+		public @Bean Bar bar() {
 			return new Bar(foo());
 		}
 	}
@@ -564,23 +600,40 @@ public class ConfigurationClassPostProcessorTests {
 	@Order(2)
 	static class OverridingSingletonBeanConfig {
 
-		public @Bean
-		ExtendedFoo foo() {
+		public @Bean ExtendedFoo foo() {
 			return new ExtendedFoo();
 		}
 
-		public @Bean
-		Bar bar() {
+		public @Bean Bar bar() {
 			return new Bar(foo());
 		}
 	}
 
+	@Configuration
+	static class OverridingAgainSingletonBeanConfig {
+
+		public @Bean ExtendedAgainFoo foo() {
+			return new ExtendedAgainFoo();
+		}
+	}
+
+	@Configuration
+	static class InvalidOverridingSingletonBeanConfig {
+
+		public @Bean Foo foo() {
+			return new Foo();
+		}
+	}
+
 	static class Foo {
 	}
 
 	static class ExtendedFoo extends Foo {
 	}
 
+	static class ExtendedAgainFoo extends ExtendedFoo {
+	}
+
 	static class Bar {
 
 		final Foo foo;