Add JSpecify annotations to defaults

[jvz]

As noted in https://issues.apache.org/jira/browse/LOG4J2-1477, JSpecify is the project specifying the one true nullability annotation standard. I experimented with creating copies of those annotations that use the JSR 305 nullability annotations to implement it, but it seems like it'd be easier to just use these annotations directly since they're only required at compile time. The use of these annotations would supersede any use of the old JSR annotations.

[ppkarwasz]

@jvz, can you list which tools currently support those annotations? I am mostly interested in Eclipse, IDEA, Spotbugs and some tool like NullAway or Checker Framework that guarantees that the code is NPE-free.

[jvz]

I have no idea if any support this yet. I like the annotation scheme at least, though, if we want to use our own packaged annotations instead based on JSR 305 like I tried out before. That approach at least works with existing tools until JSpecify is directly supported.

[jvz]

I just noticed that this can be done directly in Log4j for now. This will make it simpler to apply any rewrites to the annotations as tooling catches up. See apache/logging-log4j2@2da4108 for the aliasing.

[GregDThomas]

which tools currently support those annotations? I am mostly interested in Eclipse, IDEA, Spotbugs and some tool like NullAway or Checker Framework t

IntelliJ supports it (JetBrains are a member of the jspecify group - https://jspecify.dev/about)
There's details on a fork of the checker framework at https://github.com/jspecify/jspecify-reference-checker

No idea on Spotbugs/Eclipse I'm afraid.