.groovy

FormField formComponent = getFieldById(fieldChanged)
FormField formSubcomponent = getFieldByName("Subcomponent")

Object componentFormValue = formComponent.getFormValue()
List componentIds = []

if (componentFormValue instanceof List) {
    componentIds.addAll(componentFormValue as List)
}
else {
    // could be an empty string if all components are deselected
    if (componentFormValue) {
        componentIds.add(componentFormValue)
    }
}

Map fieldOptions = [:]
// fieldOptions.put("-1", "None")


def customField = customFieldManager.getCustomFieldObject(formSubcomponent.getFieldId())
def config = customField.getRelevantConfig(getIssueContext())
def options = optionsManager.getOptions(config)
def optionIdByName = [:]
options.each {
    optionIdByName.put(it.value, it.optionId.toString())
}

componentIds.each { componentId ->
    try {
        Long.parseLong(componentId as String)
    } catch (NumberFormatException e) {
        log.error("Could not get component Id as Long")
        return
    }
    def component = getProjectComponent(Long.parseLong(componentId as String))

    log.debug "name: \"" + component?.name + "\""
    switch (component?.name) {
        case "Comp1":
            fieldOptions.putAll([(optionIdByName["Lemons"]): "Lemons", (optionIdByName["Oranges"]): "Oranges"])
            break

        case "Comp2":
            fieldOptions.putAll([(optionIdByName["Spinach"]): "Spinach", (optionIdByName["Celery"]): "Celery"])
            break

    }
}
log.debug("Will set fieldOptions: $fieldOptions")
formSubcomponent.setFieldOptions(fieldOptions)