UnnecessaryDefaultInEnumSwitch provides illegal suggestion for arrow rules in switch statements

[PhilippWendler]

In the following example, the check UnnecessaryDefaultInEnumSwitch suggests to remove the default clause with the reason "Switch handles all enum values: the default case can be omitted to enable enforcement at compile-time that the switch statement is exhaustive." But the code would not compile then:

public class Test {

  enum TestEnum {
    FOO,
    BAR;
  }

  void unnecessaryDefault() {
    String x;

    switch (TestEnum.FOO) {
      case FOO -> x = "FOO";
      case BAR -> x = "BAR";
      default -> throw new AssertionError();
    }

    System.out.println(x);
  }
}

It seems the reason is the incomplete handling of arrow rules from e5d52dd in

error-prone/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryDefaultInEnumSwitch.java

Lines 159 to 163 in cecce2e

	List<? extends StatementTree> defaultStatements = defaultCase.getStatements();
	if (defaultStatements == null) {
	// TODO(b/177258673): provide fixes for `case -> ...`
	return buildDescription(defaultCase).setMessage(DESCRIPTION_REMOVED_DEFAULT).build();
	}

[graememorgan]

Thanks for the report. We had a TODO to improve handling around this, and hopefully it's now TODONE. :)