Better error reporting when instance does not match factory method

This commit improves the handling of IllegalArgumentException in
SimpleInstantiationStrategy. Previously, only arguments mismatch were
handled but the exception can also be thrown if the factory instance
does not match the target method.

Closes gh-28897

Author: snicoll

spring-beans/src/main/java/org/springframework/beans/factory/support/SimpleInstantiationStrategy.java

@@ -36,6 +36,7 @@
  *
  * @author Rod Johnson
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 1.1
  */
 public class SimpleInstantiationStrategy implements InstantiationStrategy {
@@ -152,6 +153,12 @@ public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, Bean
 			}
 		}
 		catch (IllegalArgumentException ex) {
+			if (factoryBean != null
+					&& !factoryMethod.getDeclaringClass().isAssignableFrom(factoryBean.getClass())) {
+				throw new BeanInstantiationException(factoryMethod,
+						"Illegal factory instance for factory method '" + factoryMethod.getName() + "'; " +
+						"instance: " + factoryBean.getClass().getName(), ex);
+			}
 			throw new BeanInstantiationException(factoryMethod,
 					"Illegal arguments to factory method '" + factoryMethod.getName() + "'; " +
 					"args: " + StringUtils.arrayToCommaDelimitedString(args), ex);

spring-beans/src/test/java/org/springframework/beans/factory/support/SimpleInstantiationStrategyTests.java

@@ -53,6 +53,14 @@ void instantiateWitArgs() {
 		assertThat(simpleBean).isEqualTo("Test42");
 	}
 
+	@Test
+	void instantiateWitSubClassFactoryArgs() {
+		RootBeanDefinition bd = new RootBeanDefinition(String.class);
+		Object simpleBean = instantiate(bd, new ExtendedSampleFactory(),
+				method(SampleFactory.class, "beanWithTwoArgs"), "Test", 42);
+		assertThat(simpleBean).isEqualTo("42Test");
+	}
+
 	@Test
 	void instantiateWithNullValueReturnsNullBean() {
 		RootBeanDefinition bd = new RootBeanDefinition(String.class);
@@ -71,6 +79,28 @@ bd, new SampleFactory(),
 				.withMessageContaining("args: 42,Test");
 	}
 
+	@Test
+	void instantiateWithTargetTypeMismatch() {
+		RootBeanDefinition bd = new RootBeanDefinition(String.class);
+		assertThatExceptionOfType(BeanInstantiationException.class).isThrownBy(() -> instantiate(
+						bd, new AnotherFactory(),
+						method(SampleFactory.class, "beanWithTwoArgs"), "Test", 42))
+				.withMessageContaining("Illegal factory instance for factory method 'beanWithTwoArgs'")
+				.withMessageContaining("instance: " + AnotherFactory.class.getName())
+				.withMessageNotContaining("args: Test,42");
+	}
+
+	@Test
+	void instantiateWithTargetTypeNotAssignable() {
+		RootBeanDefinition bd = new RootBeanDefinition(String.class);
+		assertThatExceptionOfType(BeanInstantiationException.class).isThrownBy(() -> instantiate(
+						bd, new SampleFactory(),
+						method(ExtendedSampleFactory.class, "beanWithTwoArgs"), "Test", 42))
+				.withMessageContaining("Illegal factory instance for factory method 'beanWithTwoArgs'")
+				.withMessageContaining("instance: " + SampleFactory.class.getName())
+				.withMessageNotContaining("args: Test,42");
+	}
+
 	@Test
 	void instantiateWithException() {
 		RootBeanDefinition bd = new RootBeanDefinition(String.class);
@@ -115,4 +145,20 @@ String errorBean(String msg) {
 		}
 
 	}
+
+	static class ExtendedSampleFactory extends SampleFactory {
+
+		@Override
+		String beanWithTwoArgs(String first, Integer second) {
+			return second + first;
+		}
+	}
+
+	static class AnotherFactory {
+
+		String beanWithTwoArgs(String first, Integer second) {
+			return second + first;
+		}
+
+	}
 }