Regression of erroneous implicit constructor binding for @ConfigurationProperties between 3.0.5 and 3.1.1

[GrantFleming]

There were issues previously where spring would attempt constructor binding of @ConfigurationProperties under some circumstances where it should not.

Related to issues #33710 #33509

Issue seems to have surfaced in 3.0.0 and seems to have been fixed in 3.0.2, and remains fixed through to 3.0.5 inclusive.

In 3.1.1 this behaviour seems to have regressed.

Can be reproduced with the following kotlin example:

@SpringBootApplication
class ConstructorbindingApplication

fun main(args: Array<String>) {
	runApplication<ConstructorbindingApplication>(*args)
}

@Component
@ConfigurationProperties("top-level-property")
class ApplicationProperties(
	var someProperty: String = ""
) {}

Application runs successfully in 3.0.5, however in 3.1.1 throws the following exception:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'applicationProperties' defined in file [C:\Users\grant\Desktop\constructorbinding\constructorbinding\target\classes\com\example\constructorbinding\ApplicationProperties.class]: Cannot bind @ConfigurationProperties for bean 'applicationProperties'. Ensure that @ConstructorBinding has not been applied to regular bean
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:605) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:520) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:326) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:324) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:973) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:941) ~[spring-context-6.0.10.jar:6.0.10]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:608) ~[spring-context-6.0.10.jar:6.0.10]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-3.1.1.jar:3.1.1]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:436) ~[spring-boot-3.1.1.jar:3.1.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:312) ~[spring-boot-3.1.1.jar:3.1.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-3.1.1.jar:3.1.1]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-3.1.1.jar:3.1.1]
	at com.example.constructorbinding.ConstructorbindingApplicationKt.main(ConstructorbindingApplication.kt:23) ~[classes/:na]
Caused by: java.lang.IllegalStateException: Cannot bind @ConfigurationProperties for bean 'applicationProperties'. Ensure that @ConstructorBinding has not been applied to regular bean
	at org.springframework.util.Assert.state(Assert.java:76) ~[spring-core-6.0.10.jar:6.0.10]
	at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.bind(ConfigurationPropertiesBindingPostProcessor.java:92) ~[spring-boot-3.1.1.jar:3.1.1]
	at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:79) ~[spring-boot-3.1.1.jar:3.1.1]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:419) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1762) ~[spring-beans-6.0.10.jar:6.0.10]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:598) ~[spring-beans-6.0.10.jar:6.0.10]
	... 14 common frames omitted

The author of one of the original issues has also noted the regression on the now-closed issue.

Workarounds

1. Provide a default @Autowired no-arg constructor:

@Component
@ConfigurationProperties("top-level-property")
class ApplicationProperties(
	var someProperty: String = ""
) {
	@Autowired
	constructor() : this("")
}

2. Annotate the class with @configuration rather than @component:

@Configuration
@ConfigurationProperties("top-level-property")
class ApplicationProperties(
	var someProperty: String = ""
) {
}

[wilkinsona]

Thanks for the report. The problem does not occur with 3.0.9-SNAPSHOT or 3.1.2-SNAPSHOT (available from https://repo.spring.io/snapshot). It has already been fixed by the changes made for #36175.