Affects PMD Version:

7.18.0

Rule:
UnusedLocalVariable

Description:

When using an instanceof guard with pattern matching in a switch expression, then the local variable matched by that pattern will be marked as unused by PMD.

Code Sample demonstrating the issue:

public class Reproducer {
    public static boolean customEquals(Object foo, Object bar) {
        return switch (foo) {
            case String fooString when bar instanceof String barString -> fooString.equals(barString);
            default -> false;
        };
    }
}

Expected outcome:

PMD reports a violation at line 4, but that's wrong. That's a false positive.

Running PMD through: Gradle 9.2.1 and Java 21