Dubious 'unused' diagnostics disappear when opening files

[fbricon]

There are a couple issues with the 'unused' code detection:

• imports used by Javadoc are flagged as unused by the workspace build, but when opening the file, diagnostics disappear
• actual unused code is not flagged as unused while the file is opened

https://github.com/user-attachments/assets/373ff4ba-c3e7-41a8-ae31-3b86b5cd23d2

Tested against https://github.com/eclipse/lemminx

[fbricon]

Also private constructors should not be flagged as unused

[testforstephen]

Initially you see the unused diagnostics in the problems view, they're reported by the build job. When you open the Java file, it disappears because the DOM parser does not enable the unused checker and cleanup the diagnostics of current file.

https://github.com/eclipse-jdtls/eclipse-jdt-core-incubator/blob/343016820349fce63f9ff5095c905ded7d646500/org.eclipse.jdt.core.javac/src/org/eclipse/jdt/core/dom/JavacCompilationUnitResolver.java#L498-L505

I hooked the unused checker into the DOM parser by listening at the ANALYZE task. It looks like the ANALYZE task is never invoked by DOM parser. This should work before, no idea why it's not called in latest code.

@mickaelistria any thoughts?

[mickaelistria]

At the moment, the analyze is called while resolving bindings. So when bindings are disabled, analyze() is never run. We should probably also consider FORCE_PROBLEM_DETECTION flag to run that analyze code.

[mickaelistria]

https://github.com/eclipse-jdtls/eclipse-jdt-core-incubator/pull/771 might help. @testforstephen Can you please check?

[testforstephen]

After debugging the code, it's because the analyze in DOM parser stops on error and return earlier. In the build job, we have overwritten the compiler to force it to proceed on error. But for the DOM parser, we don't do that and it will return earlier if the errorCount() of JavaCompiler > 0.

[fbricon]

Also private static final long serialVersionUID fields on Serializable classes should be ignored

[testforstephen]

this should be fixed by recent commits https://github.com/eclipse-jdtls/eclipse-jdt-core-incubator/commit/cb3c54ff805b938febe42cabb52e760df1614b29, https://github.com/eclipse-jdtls/eclipse-jdt-core-incubator/commit/5cadbcc0c5a3cfcf628141f29e686873990b52d2