JEP 406 introduced a new preview feature in Java 17 called Pattern Matching for switch. Checkstyle added support for this in Issue #10848 and PR #11100. Since then, however, the feature got refined multiple times in:

• JEP 420: Pattern Matching for switch (Second Preview)
• JEP 427: Pattern Matching for switch (Third Preview)
• JEP 433: Pattern Matching for switch (Fourth Preview)

In those refinements, some syntax was dropped, which led to some of the test cases added in PR #11100 becoming non-compileable.

In PR #18103, we:

• Extracted the non-compilable test cases in separate files - *NoLongerSupportedByJava.java. This was done to preserve parser coverage.
• Updated all non-compilable test cases to match updated syntax and moved them to the compilable resources/

What remains is to:

• Remove syntax from MissingSwitchDefault
  • Issue #18104: Remove old syntax from MissingSwitchDefault #18131
• Remove syntax from OperatorWrapCheck
  • Issue #18104: Remove old syntax from OperatorWrapCheck #18139
• Remove grammar that was added in Issue #10848: Support patterns in switch #11100
  • This must be done in a separate ticket as stated in Drop support in checks for no-longer-compilable preview feature - Pattern matching for swtich #18104 (comment)