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The Dart analyzer will soon be changed so that if the `default` clause of a `switch` statement is determined to be unreachable by the exhaustiveness checker, a new warning of type `unreachable_switch_default` will be issued. This parallels the behavior of the existing `unreachable_switch_case` warning, which is issued whenever a `case` clause of a `switch` statement is determined to be unreachable. Before adding the new warning to the analyzer, code in the engine needs to first be updated to eliminate these unreachable `default` clauses, so that the warning won't cause builds to break. For more information, see https://github.com/dart-lang/sdk/issues/54575.