ConstructorResolver rejects a candidate if the parameter value is null

[sbrannen]

Now that #31472 has been resolved, AOT processing for Spr9799XmlConfigTests (in spring-test) fails with the following stack trace when run via AotIntegrationTests#endToEndTestsForEntireSpringTestModule().

org.springframework.test.context.aot.TestContextAotException: Failed to generate AOT artifacts for test classes [org.springframework.test.context.junit4.spr9799.Spr9799XmlConfigTests]
	at org.springframework.test.context.aot.TestContextAotGenerator.lambda$10(TestContextAotGenerator.java:284)
	at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:721)
	at org.springframework.util.MultiValueMapAdapter.forEach(MultiValueMapAdapter.java:179)
	at org.springframework.test.context.aot.TestContextAotGenerator.processAheadOfTime(TestContextAotGenerator.java:243)
	at org.springframework.test.context.aot.TestContextAotGenerator.processAheadOfTime(TestContextAotGenerator.java:205)
	at org.springframework.test.context.aot.AotIntegrationTests.endToEndTestsForEntireSpringTestModule(AotIntegrationTests.java:151)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.springframework.core.test.tools.CompileWithForkedClassLoaderExtension.intercept(CompileWithForkedClassLoaderExtension.java:97)
	at org.springframework.core.test.tools.CompileWithForkedClassLoaderExtension.interceptTestMethod(CompileWithForkedClassLoaderExtension.java:83)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
Caused by: org.springframework.test.context.aot.TestContextAotException: Failed to process test class [org.springframework.test.context.junit4.spr9799.Spr9799XmlConfigTests] for AOT
	at org.springframework.test.context.aot.TestContextAotGenerator.processAheadOfTime(TestContextAotGenerator.java:321)
	at org.springframework.test.context.aot.TestContextAotGenerator.lambda$10(TestContextAotGenerator.java:276)
	... 10 more
Caused by: java.lang.IllegalStateException: No constructor or factory method candidate found for Root bean: class [org.springframework.web.servlet.handler.MappedInterceptor]; scope=singleton; abstract=false; lazyInit=null; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodNames=null; destroyMethodNames=null and argument types [?, org.springframework.web.servlet.handler.ConversionServiceExposingInterceptor]
	at org.springframework.beans.factory.support.ConstructorResolver.resolveConstructorOrFactoryMethod(ConstructorResolver.java:994)
	at org.springframework.beans.factory.support.RegisteredBean.resolveConstructorOrFactoryMethod(RegisteredBean.java:212)
	at org.springframework.util.function.SingletonSupplier.get(SingletonSupplier.java:106)
	at org.springframework.beans.factory.aot.DefaultBeanRegistrationCodeFragments.getTarget(DefaultBeanRegistrationCodeFragments.java:80)
	at org.springframework.beans.factory.aot.BeanDefinitionMethodGenerator.generateBeanDefinitionMethod(BeanDefinitionMethodGenerator.java:85)
	at org.springframework.beans.factory.aot.BeanRegistrationsAotContribution.lambda$3(BeanRegistrationsAotContribution.java:90)
	at java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:721)
	at org.springframework.beans.factory.aot.BeanRegistrationsAotContribution.generateRegisterBeanDefinitionsMethod(BeanRegistrationsAotContribution.java:88)
	at org.springframework.beans.factory.aot.BeanRegistrationsAotContribution.lambda$1(BeanRegistrationsAotContribution.java:73)
	at org.springframework.aot.generate.GeneratedMethod.<init>(GeneratedMethod.java:54)
	at org.springframework.aot.generate.GeneratedMethods.add(GeneratedMethods.java:112)
	at org.springframework.aot.generate.GeneratedMethods.add(GeneratedMethods.java:89)
	at org.springframework.beans.factory.aot.BeanRegistrationsAotContribution.applyTo(BeanRegistrationsAotContribution.java:72)
	at org.springframework.context.aot.BeanFactoryInitializationAotContributions.applyTo(BeanFactoryInitializationAotContributions.java:78)
	at org.springframework.context.aot.ApplicationContextAotGenerator.lambda$0(ApplicationContextAotGenerator.java:58)
	at org.springframework.context.aot.ApplicationContextAotGenerator.withCglibClassHandler(ApplicationContextAotGenerator.java:67)
	at org.springframework.context.aot.ApplicationContextAotGenerator.processAheadOfTime(ApplicationContextAotGenerator.java:53)
	at org.springframework.test.context.aot.TestContextAotGenerator.processAheadOfTime(TestContextAotGenerator.java:318)
	... 11 more

[snicoll]

What does the generated code for MappedInterceptor look like?

I can see it sets the first argument to null and then a reference to a ConversionServiceExposingInterceptor bean which is an HandlerInterceptor so constructor resolution should find a matching constructor there.

[sbrannen]

What does the generated code for MappedInterceptor look like?

It doesn't get that far. It fails while attempting to generate code.

[snicoll]

That's the null there indeed. Replacing that with an empty String array is enough to get past the issue. With null we don't have any type matching, but I believe there might be some sort of fallback to try considering that all 5 constructors take a String[] as the first argument.

[snicoll]

This was an interesting dive in ConstructorResolver. As a null value does not carry a type, it breaks any attempt to match a constructor. Ignoring the null value and proceeding with the non-null value is enough to make progress, including supporting this use case.