[java] ImplicitSwitchFallThrough: False-positive with nested switch statements

[sratz]

Affects PMD Version: 7.0.0

Rule: category/java/errorprone.xml/ImplicitSwitchFallThrough

Description:

Code Sample demonstrating the issue:

public class Test {

	boolean foo(String a, String b) {

		switch (a) {
		case "a1":
			return true;
		case "a2":
			switch (b) {
			case "b1":
				return true;
			default:
				return false;
			}
		default:   // <--- false-positive ImplicitSwitchFallThrough
			return false;
		}
	}

}

Outcome:

PMD reports a violation at line 15, but that's wrong. That's a false positive.

the outer case "a2" cannot fall through, since the inner switch is exhaustive and returns from all branches.

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