DLS_DEAD_LOCAL_STORE issue in Java 21 with pattern matching

[CamilYed]

In our Java codebase, we're utilizing pattern matching introduced in Java 21. While compiling the code, we encountered a "DLS_DEAD_LOCAL_STORE" warning pointing to the parameter named "ignored" within a specific switch case block. Despite its declaration, the "ignored" parameter is not utilized within the associated code block.

sealed interface Result {

    record Success() implements Result {
    }

    record Failure(String message) implements Result  {
    }

}

  void handle(Result result) {
      switch(result) {
          case Result.Success ignored -> { log.info ("Success"); }
          case Result.Failure failure -> { log.error ("Failure {}", failure.message()); }
      }

  }

Expected Behavior

As long as there are no unnamed variables in Java
https://openjdk.org/jeps/456

We should in the case of a switch block be able to allow the use of a variable, for example, named ignored.

Unnamed pattern variables
An unnamed pattern variable can appear in a type pattern (JLS §14.30.1), including var type patterns, regardless of whether the type pattern appears at the top level or is nested in a record pattern. For example, the Ball example can now be written:

// JEP 456  JDK 22
switch (ball) {
    case RedBall _   -> process(ball);          // Unnamed pattern variable
    case BlueBall _  -> process(ball);          // Unnamed pattern variable
    case GreenBall _ -> stopProcessing();       // Unnamed pattern variable
}

or

// JDK 21
switch (ball) {
    case RedBall ignored  -> process(ball);          // ignored
    case BlueBall ignored-> process(ball);           // ignored
    case GreenBall ignored -> stopProcessing();       // ignored
}

This is a similar pattern when we catch an exception that we do nothing about.

  try {
      foo();
  } catch(SomeException ignored) {

  }

Steps to Reproduce

Compile the provided Java code using Java 21.
Observe the "DLS_DEAD_LOCAL_STORE" warning associated with the "ignored" parameter.
Thank you for your attention to this matter. Please let us know if you need any further information or clarification regarding this issue.

Best regards,
Kamil Jedrzejuk

[welcome]

Thanks for opening your first issue here! 😃
Please check our contributing guideline. Especially when you report a problem, make sure you share a Minimal, Complete, and Verifiable example to reproduce it in this issue.

[gtoison]

Hello, I think this is the same issue as #2736
This should be fixed by #2828 once it is released