Java 21

[TwoOfTwelve]

To update java for java 21 the following things have to be done:

• Update java version in pom.xml
• Update java version in workflow files
• Update expected java version for tests
• Verify the old tests are still working
• Write rules and tests for new java features
• Verify the rules below indeed do not impact jplag
• Enable Previews
• Right now the java version for enabling previews is hard coded. It should be unified with the version in NewJavaFeaturesTest

The following new features are relevant to jplag:

• Record Patterns and Pattern matching for switch have been finalized
  Works without changes
• String templates (preview)
  Works without changes
• Unnamed patterns and variables (preview)
  Ignore vardefs without name (javac maps "_" to an empty string)
• Anonymous classes. Produced negative positions for end of class tokens
• Guards for cases. Should be extracted as an additional if.

The following changes should not impact jplag:

• Virtual threads / Structured concurrency
• Foreign function api (preview) [maybe poses problems for obfuscation of plagiarisms]
• Scoped values

[TwoOfTwelve]

Solves #1319

[SirYwell]

There are a few things that aren't really covered:

• case pattern with guards (case Integer i when i > 0:)
  • it might make sense to desugar it into an if
• JEP 445 (though it might make sense to skip that, there are a few changes to how the compiler handles it in Java 22)

Is that intentional?

[TwoOfTwelve]

Thank you. I missed those two things. JPlag works with anonymous classes. There was just a minor error with negative code positions. The order of tokens might be weird, but as this is still just a preview feature I think that is ok.

For guards I added a rule to generate an additional IF and IF_END token, the same way it would be done if there was an if in the case body instead.

[Kr0nox]

Just one small thing

[dfuchss]

-> https://github.com/jplag/JPlag/actions/runs/7057421814/workflow#L54

It seems that you've missed one last line :)