Spring Cloud Sleuth has a required dependency on AspectJ

[snicoll]

Adding spring-cloud-sleuth-core to a Spring Boot application leads to the following:

Caused by: java.lang.NoClassDefFoundError: org/aspectj/weaver/tools/PointcutPrimitive
	at org.springframework.aop.aspectj.AspectJExpressionPointcut.<clinit>(AspectJExpressionPointcut.java:91) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.aspectj.annotation.ReflectiveAspectJAdvisorFactory.getPointcut(ReflectiveAspectJAdvisorFactory.java:212) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.aspectj.annotation.ReflectiveAspectJAdvisorFactory.getAdvisor(ReflectiveAspectJAdvisorFactory.java:194) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.aspectj.annotation.ReflectiveAspectJAdvisorFactory.getAdvisors(ReflectiveAspectJAdvisorFactory.java:126) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.aspectj.annotation.BeanFactoryAspectJAdvisorsBuilder.buildAspectJAdvisors(BeanFactoryAspectJAdvisorsBuilder.java:110) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator.findCandidateAdvisors(AnnotationAwareAspectJAutoProxyCreator.java:95) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.aspectj.autoproxy.AspectJAwareAdvisorAutoProxyCreator.shouldSkip(AspectJAwareAdvisorAutoProxyCreator.java:101) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessBeforeInstantiation(AbstractAutoProxyCreator.java:251) ~[spring-aop-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInstantiation(AbstractAutowireCapableBeanFactory.java:1141) ~[spring-beans-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation(AbstractAutowireCapableBeanFactory.java:1114) ~[spring-beans-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:506) ~[spring-beans-5.2.6.BUILD-20200423.171221-90.jar:5.2.6.BUILD-SNAPSHOT]
	... 36 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.aspectj.weaver.tools.PointcutPrimitive
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[na:1.8.0_232]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418) ~[na:1.8.0_232]
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352) ~[na:1.8.0_232]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351) ~[na:1.8.0_232]
	... 47 common frames omitted

Debugging, this is related to the use of @Aspect that requires AspectJ. TraceSchedulingAutoConfiguration is opting-in for AspectJ but does not enforce that with a class check.

I think this should be revisited to either back-off or provide AspectJ by default. I've added a condition on my end to back-off if AspectJ isn't available.

[codefromthecrypt]

sorry what do you mean by back off.

[spencergibb]

Conditional on class some class from aspectj

[codefromthecrypt]

gotit (ps sorry about missing things, I forgot I set watch to releases only a couple months ago! 😊 )

[snicoll]

So there is a class check condition on the bean method but that's useless since the class-level @EnableAspectJAutoProxy is going to trigger things before the condition gets a chance to be evaluated.

If the intent was to back off if aspectJ is not present, then the condition should be moved elsewhere and a test where we simulate the removal of AspectJ (via a filtered ClassLoader for instance) should be added.

I should also note that this annotation is overriding what the AOP auto-configuration in Spring Boot does. Nothing wrong about doing that but it's doing that unilaterally in an auto-configuration so I don't think that was the original intent.

[codefromthecrypt]

mind raising a PR with the simplest way out, if that means deleting something works for me. If we have no test coverage to show that it is needed somehow, something will break and then we can add the missing tests.

[timtebeek]

Just opened up #1624 since the tests and fix were similar enough to fe63513 to make this low effort, even though I've not used TraceSchedulingAutoConfiguration myself. So a slightly more stringent review might be needed to ensure the PR fixes the issue as desired. :)

[timtebeek]

This issue can likely be closed after 75756fd ; The pull request that referenced this issue above was merged to master locally to fix up a last few checkstyle issues.

[codefromthecrypt]

we can close this as next release will take it. Thanks @timtebeek and @snicoll