Failure analysis for a BindException with an unexpected root cause (such as ArrayIndexOutOfBoundsException) is unhelpful

Question

Failure analysis for a BindException with an unexpected root cause (such as ArrayIndexOutOfBoundsException) is unhelpful

sbueringer opened this issue 6 years ago · comments

Hi,

I'm using Spring Boot 2.0.2 with Kotlin 1.2.41. I'm trying to use an enum as ConfigurationProperty. I wrote a minimal example application to reproduce the issue:
https://github.com/sbueringer/springboot-kotlin-enum/

I have the following ConfigurationProperties:

@Configuration
@ConfigurationProperties(prefix = "custom")
@Validated
class Properties {
    var test = TestEnum.VALUE1
}
enum class TestEnum {VALUE1, VALUE2}

In combination with the following application.yaml:

custom:
  test: VALUE2

I get the following exception on startup:

2018-05-25 06:45:21.848  WARN 22061 --- [  restartedMain] onfigReactiveWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'application': Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.boot.context.properties.ConfigurationPropertiesBindException: Error creating bean with name 'properties': Could not bind properties to 'Properties' : prefix=custom, ignoreInvalidFields=false, ignoreUnknownFields=true; nested exception is org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'custom.test' to com.example.TestEnum

To reproduce, just clone the repository and startup the SpringBootApplication.

Edit: It seems to work, if I remove the @Validated annotation. Is that intended?

Stéphane Nicoll · Answer 1 · Fri May 25 2018 17:02:00 GMT+0800 (China Standard Time)

Please review the documentation

Carlos Ferreyra · Answer 2 · Wed Jul 04 2018 21:06:08 GMT+0800 (China Standard Time)

This was closed too fast. After changing the configuration property to lateinit var the error is different. I just came upon this issue while migrating an application to Spring Boot 2.

@Configuration
@ConfigurationProperties(prefix = "custom")
@Validated
class Properties {
    lateinit var test: TestEnum
}

Error:

***************************
APPLICATION FAILED TO START
***************************

Description:

Failed to bind properties under 'custom.test' to com.example.TestEnum:

    Property: custom.test
    Value: VALUE2
    Origin: class path resource [application.yaml]:3:9
    Reason: 0

Here's my version of the same repo with this change: https://github.com/crypticmind/springboot-kotlin-enum

Carlos Ferreyra · Answer 3 · Wed Jul 04 2018 21:06:34 GMT+0800 (China Standard Time)

@snicoll Please take a look and let me know if I should open a new issue instead.

Phil Webb · Answer 4 · Wed Jul 04 2018 22:00:57 GMT+0800 (China Standard Time)

Running with debug gives:

org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'custom.test' to com.example.TestEnum
        at org.springframework.boot.context.properties.bind.Binder.handleBindError(Binder.java:250) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bind(Binder.java:226) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.lambda$bindBean$4(Binder.java:334) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.JavaBeanBinder.bind(JavaBeanBinder.java:73) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.JavaBeanBinder.bind(JavaBeanBinder.java:62) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.JavaBeanBinder.bind(JavaBeanBinder.java:54) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.lambda$null$5(Binder.java:342) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[na:1.8.0_144]
        at java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1351) ~[na:1.8.0_144]
        at java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:126) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:498) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:485) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[na:1.8.0_144]
        at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_144]
        at java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:464) ~[na:1.8.0_144]
        at org.springframework.boot.context.properties.bind.Binder.lambda$bindBean$6(Binder.java:343) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder$Context.withIncreasedDepth(Binder.java:442) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder$Context.withBean(Binder.java:428) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder$Context.access$400(Binder.java:382) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bindBean(Binder.java:340) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bindObject(Binder.java:279) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bind(Binder.java:221) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bind(Binder.java:210) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bind(Binder.java:192) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.ConfigurationPropertiesBinder.bind(ConfigurationPropertiesBinder.java:82) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.bind(ConfigurationPropertiesBindingPostProcessor.java:107) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor.postProcessBeforeInitialization(ConfigurationPropertiesBindingPostProcessor.java:93) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:422) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1698) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:579) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:815) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:721) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:192) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1274) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1131) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:541) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760) ~[spring-beans-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869) ~[spring-context-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.refresh(ReactiveWebServerApplicationContext.java:61) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at com.example.ApplicationKt.main(Application.kt:13) [main/:na]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_144]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_144]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_144]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_144]
        at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.0.2.RELEASE.jar:2.0.2.RELEASE]
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
        at java.util.Arrays$ArrayList.get(Arrays.java:3841) ~[na:1.8.0_144]
        at org.hibernate.validator.internal.metadata.aggregated.ParameterMetaData$Builder.build(ParameterMetaData.java:169) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.metadata.aggregated.ExecutableMetaData$Builder.findParameterMetaData(ExecutableMetaData.java:435) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.metadata.aggregated.ExecutableMetaData$Builder.build(ExecutableMetaData.java:388) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.metadata.aggregated.BeanMetaDataImpl$BuilderDelegate.build(BeanMetaDataImpl.java:788) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.metadata.aggregated.BeanMetaDataImpl$BeanMetaDataBuilder.build(BeanMetaDataImpl.java:648) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.metadata.BeanMetaDataManager.createBeanMetaData(BeanMetaDataManager.java:192) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.metadata.BeanMetaDataManager.lambda$getBeanMetaData$0(BeanMetaDataManager.java:160) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at java.util.concurrent.ConcurrentMap.computeIfAbsent(ConcurrentMap.java:324) ~[na:1.8.0_144]
        at org.hibernate.validator.internal.metadata.BeanMetaDataManager.getBeanMetaData(BeanMetaDataManager.java:159) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.engine.ValidationContext$ValidationContextBuilder.forValidate(ValidationContext.java:566) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.hibernate.validator.internal.engine.ValidatorImpl.validate(ValidatorImpl.java:155) ~[hibernate-validator-6.0.9.Final.jar:6.0.9.Final]
        at org.springframework.validation.beanvalidation.SpringValidatorAdapter.validate(SpringValidatorAdapter.java:104) ~[spring-context-5.0.6.RELEASE.jar:5.0.6.RELEASE]
        at org.springframework.boot.context.properties.ConfigurationPropertiesJsr303Validator.validate(ConfigurationPropertiesJsr303Validator.java:52) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.validation.ValidationBindHandler.lambda$validate$1(ValidationBindHandler.java:101) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184) ~[na:1.8.0_144]
        at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175) ~[na:1.8.0_144]
        at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[na:1.8.0_144]
        at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) ~[na:1.8.0_144]
        at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) ~[na:1.8.0_144]
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_144]
        at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418) ~[na:1.8.0_144]
        at org.springframework.boot.context.properties.bind.validation.ValidationBindHandler.validate(ValidationBindHandler.java:101) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.validation.ValidationBindHandler.validate(ValidationBindHandler.java:83) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.validation.ValidationBindHandler.onFinish(ValidationBindHandler.java:72) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.handleBindResult(Binder.java:236) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        at org.springframework.boot.context.properties.bind.Binder.bind(Binder.java:223) ~[spring-boot-2.0.2.RELEASE.jar:2.0.2.RELEASE]
        ... 61 common frames omitted

Andy Wilkinson · Answer 5 · Wed Jul 04 2018 22:01:13 GMT+0800 (China Standard Time)

The failure analysis could certainly be better.

The failure occurs when Hibernate Validator is trying to get a name for the 1st (index 0) parameter of the constructor protected com.example.TestEnum(java.lang.String,int). This results in a call to getParameterNames(Constructor<?> constructor) in this code in Spring Framework's LocalValidatorFactoryBean:

configuration.parameterNameProvider(new ParameterNameProvider() {
	@Override
	public List<String> getParameterNames(Constructor<?> constructor) {
		String[] paramNames = discoverer.getParameterNames(constructor);
		return (paramNames != null ? Arrays.asList(paramNames) :
				defaultProvider.getParameterNames(constructor));
	}
	@Override
	public List<String> getParameterNames(Method method) {
		String[] paramNames = discoverer.getParameterNames(method);
		return (paramNames != null ? Arrays.asList(paramNames) :
				defaultProvider.getParameterNames(method));
	}
});

discoverer, a PrioritizedParameterNameDiscoverer, returns a zero-length string array. When Hibernate Validator tries to retrieve the entry at index 0 of the array it fails with the above exception. The empty array comes from the delegate KotlinReflectionParameterNameDiscoverer as its getParameterNames(List<KParameter>) method is called with an empty list.

I'm not sure if this is a Kotlin bug or a Spring Framework bug. Hopefully @sdeleuze can point things in the right direction.

Andy Wilkinson · Answer 6 · Wed Jul 04 2018 22:12:06 GMT+0800 (China Standard Time)

I've opened HV-1638 in case the Hibernate Validator team are interested in making it a bit more resilient to a name provider that returns too few names.

Sébastien Deleuze · Answer 7 · Thu Jul 05 2018 15:09:29 GMT+0800 (China Standard Time)

It could be linked to SPR-16931, and the related KT-25165 I have raised. I have added a comment mentioning this possibly new impact for us.

Andy Wilkinson · Answer 8 · Thu Jul 05 2018 16:34:58 GMT+0800 (China Standard Time)

Thank you, @sdeleuze. SPR-16931 and KT-25165 look to be exactly the problem that we're seeing.

Given that those issues have the underlying problem covered, let's use this issue to improve the failure analysis. "Reason: 0" isn't at all helpful. We should perhaps opt out of failure analysis entirely in this situation (if we can).

Andy Wilkinson · Answer 9 · Thu Jul 05 2018 16:37:11 GMT+0800 (China Standard Time)

I'm not sure if this will also happen with 1.5. Assigning to 1.5.x for now at least.

Carlos Ferreyra · Answer 10 · Thu Jul 05 2018 19:50:48 GMT+0800 (China Standard Time)

@wilkinsona about not happening in 1.5, are you referring to the underlying issue, or the obscure error message? I haven't had this issue with Kotlin enums in 1.5, and as for the error message, I understand this is generated by the error reporting in the new binding API. Obviously, checking for this in 1.5 would be satisfyingly thorough, but I'd bet this happens only in the 2.0 version.

Andy Wilkinson · Answer 11 · Thu Jul 05 2018 20:22:09 GMT+0800 (China Standard Time)

I'm referring to the obscure error message. The Kotlin support's new in Framework 5 and Boot 2.0 so it won't be a possible cause of the obscure error message. While the exception comes from the binder, the error message comes from BindFailureAnalyzer. It exists in 1.5 and 2.0, although it's not the same in each, and the input will be different hence the need to check what happens in 1.5.

Andy Wilkinson · Answer 12 · Mon Jul 09 2018 22:15:45 GMT+0800 (China Standard Time)

Unfortunately, I don't think there's much we can do about this. I can't find a good heuristic for detecting whether or not the exception message will be useful. Without one the two options we have are to leave things as they are or to always assume that it won't be useful. If we go with the latter the benefits of the analyser will be largely undone. I think we'll just have to live with this one. We can reconsider if the problem comes up again with a cause that isn't due to a bug in another library.

Ruslan Molchanov · Answer 13 · Tue Oct 09 2018 20:07:20 GMT+0800 (China Standard Time)

@wilkinsona @sbueringer @philwebb

I'm sorry for disturbing you, but I have a question.

Can we tweak KotlinReflectionParameterNameDiscoverer to solve this issue?

In my perspective, looks that all in our hands and we don't need to wait for something from Kotlin.

Looks, like if we add checking for enums, it will solve the issue.
I added the following lines at the beginning of the method and it works for me. KotlinReflectionParameterNameDiscoverer.getParameterNames(Constructor<?> ctor):

if (ctor.getDeclaringClass().isEnum()) {
    return null;
}

According to PrioritizedParameterNameDiscoverer.getParameterNames(Constructor<?> ctor) , ParameterNameDiscoverers will be applied until it one of them won't return null.

So, when KotlinReflectionParameterNameDiscoverer returns null, then the following StandardReflectionParameterNameDiscoverer will be applied and return { "$enum$name", "$enum$oridnal"} parameters for default enum and this won't cause an error.

And looks like Alexander Udalov from JetBrains had clear clarification: for Kotlin language, Enum doesn't have undeclared parameters.

So, because of this, don't you think that for Kotlin Enums we should delegate parameters discovering to Java?
Will the code above help?

Andy Wilkinson · Answer 14 · Tue Oct 09 2018 22:24:04 GMT+0800 (China Standard Time)

@ruslanys Thanks for taking a look. KotlinReflectionParameterNameDiscoverer is part of Spring Framework so this isn't the right place to discuss it. SPR-16931 is a better place for the discussion I think.

Ruslan Molchanov · Answer 15 · Tue Oct 09 2018 22:28:34 GMT+0800 (China Standard Time)

@wilkinsona Thank you for the response. 🙏