[java] Detect mismatch between Java language version used and version of classes on auxclasspath. #5612
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FYI - I started a while ago something similar -> #5299 |
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Also note that PMD is not called correctly from maven-pmd-plugin AFIK: The JDK is never added to the auxclasspath, the current runtime is always used. Maven supports toolchains, so you can select a specific JDK if you want, but it's probably not used very often. |
You're right, I forgot about this. I will close this PR then. FWIW I think doing the check in JavaLanguageProcessor and not ClasspathClassLoader is a better way since it doesn't need a specific classloader implementation. But we can do that in your PR. |
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I didn't read yet what your solution looks like in detail - I just read the summary 😄 Also, I don't remember anymore what the status of this old PR is and what's missing.... |
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We basically implemented exactly the same thing, except I did it in JavaLanguageProcessor and you did it in ClasspathClassLoader. But you added tests so I think your PR is probably a better starting point :) |
Describe the PR
This is just an idea. With ASM, we can detect the version classes on the auxclasspath were compiled with. Here I just get the class version of java.lang.Object. Assuming every JDK version ships with compiled class files that have the corresponding internal version (meaning for instance, Java 21 jrtfs ships a java.lang.Object class that was compiled with Javac 21), we can use this information to detect that the user hasn't put the correct JDK classes on their auxclasspath. We can use this to log a warning. Wdyt?
The only problem I see is that if you use PMD's default Java version, you will most likely see this warning because it is always the newest Java version. Maybe the default java version should be the latest LTS? Would this change something?
For context, I had suggested this in #4291 (comment). Putting JDK classes on the auxclasspath is recommended on our website but realistically this information is buried very deep and most people won't do it unless they see a warning.
Related issues
Ready?
./mvnw clean verifypasses (checked automatically by github actions)