OpenJDK 20 GA is scheduled for 2023/03/21.
So we should add support for that with PMD version 6.55.0 (end of February 2023).

The following JEPs are important for us:

• 432: Record Patterns (Second Preview)
• 433: Pattern Matching for switch (Fourth Preview)

In summary: https://javaalmanac.io/jdk/20/

This issue is similar to the previous: #4015

EA Release of JDK20 is available here: http://jdk.java.net/20/

Tasks:

• Add new java language versions 20 and 20-preview.
  • 20 is the new default
  • update also java.md and ant.md
  • and add in KotlinTestingDsl.kt.
• Update asm dependency to 9.4:
  • https://search.maven.org/artifact/org.ow2.asm/asm
  • https://asm.ow2.io/versions.html
  • Update net.sourceforge.pmd.lang.java.typeresolution.visitors.PMDASMVisitor.ASM_API if necessary
• Remove java language version 18-preview
  • update also java.md and ant.md
  • update KotlinTestingDsl.kt
  • remove exclusions in pmd-core/src/main/resources/internal/all-java.xml
• Update implementation for "Pattern Matching for switch" (406, 420, 427, 433) as a preview feature, mark AST classes as experimental, if needed.

  • https://openjdk.org/jeps/406 (preview 1)

  • https://openjdk.org/jeps/420 (preview 2)

  • https://openjdk.org/jeps/427 (preview 3)

  • https://openjdk.org/jeps/433 (preview 4)

    The main changes since the third preview are:

    • An exhaustive switch (i.e., a switch expression or a pattern switch statement) over an enum class now throws MatchException rather than IncompatibleClassChangeError if no switch label applies at run time.
    • The grammar for switch labels is simpler.
    • Inference of type arguments for generic record patterns is now supported in switch expressions and statements, along with the other constructs that support patterns.

  • http://cr.openjdk.java.net/~gbierman/jep432%2b433/jep432+433-20221115/specs/patterns-switch-record-patterns-jls.html

• Update implementation for "Record Patterns" (405, 432) as a preview feature, mark AST classes as experimental, if needed.

  • https://openjdk.org/jeps/405 (preview 1)

  • https://openjdk.org/jeps/432 (preview 2)

    The main changes since the first preview are to:

    • Add support for inference of type arguments of generic record patterns,
    • Add support for record patterns to appear in the header of an enhanced for statement, and
    • Remove support for named record patterns.

  • http://cr.openjdk.java.net/~gbierman/jep432%2b433/jep432+433-20221115/specs/patterns-switch-record-patterns-jls.html

• Write release notes
  • removed classes: ASTGuardedPattern
  • deprecated classes: none
  • new experimental: none
• Update https://github.com/pmd/java-regression-tests
  • no new regular language features, so no update needed
• Prepare merge for PMD 7 as a new PR: [java] Add support for java 20 (pmd7) #4379