[java] ImplicitSwitchFallThrough: False negative when fall-through comment is placed after closing brace

Affects PMD Version: 7.23.0

Rule: ImplicitSwitchFallThrough — https://docs.pmd-code.org/latest/pmd_rules_java_errorprone.html#implicitswitchfallthrough

Description:

ImplicitSwitchFallThrough does not fire when a case block contains braces without a break, and the trailing comment is placed after the closing brace.

Although the control flow still falls through from case 1 to case 2, PMD fails to detect it in this situation.

Code Sample demonstrating the issue:

public class FallThroughDemo {
    // ImplicitSwitchFallThrough is NOT reported, but fall-through still occurs
    public static String processB(int opcode, String cst) {
        String result = cst;
        switch (opcode) {
            case 1: {
                result = result.toLowerCase(); // Line7:ImplicitSwitchFallThrough should be reported
            } // and fall through...
            case 2: {
                result = result.trim();
                break;
            }
            default: {
                result = "";
                break;
            }
        }
        return result;
    }
}

Actual outcome: PMD should report a violation at line 7, but doesn't. This is a false-negative.

Running PMD through: CLI

Start with the ImplicitSwitchFallThrough rule and reproduce the Java example through the CLI, focusing on the case block with braces and the comment after its closing brace. Add coverage for this example and verify that PMD reports a violation at line 7, confirming the false negative is fixed.