private static Shape validateShape(Shape shape) {
        if (shape.isIntEnumShape()) {
            return shape;
        }
        throw new IllegalArgumentException("GenerateIntEnum requires an IntEnum shape");
    }
Directive used to generate an intEnum.

@param <C> CodegenContext type.
@param <S> Codegen settings type.
@see DirectedCodegen#generateIntEnumShape
smithy-codegen-core/src/main/java/software/amazon/smithy/codegen/core/directed/GenerateIntEnumDirective.java