private boolean expectedSetToListChange(ChangedShape<Shape> diff) {
        ShapeType oldType = diff.getOldShape().getType();
        ShapeType newType = diff.getNewShape().getType();

        // Smithy diff doesn't raise an issue if a set is changed to a list and the list
        // has the uniqueItems trait. Set is deprecated and this is a recommended change.
        if (oldType == ShapeType.SET && newType == ShapeType.LIST) {
            return diff.getNewShape().hasTrait(UniqueItemsTrait.ID);
        }

        return false;
    }
Creates an ERROR event when the type of a shape changes.
smithy-diff/src/main/java/software/amazon/smithy/diff/evaluators/ChangedShapeType.java