function getSlotVForVariableIfUsingIterationVars(slot, vFor) {
  if (!slot || !slot.directive) {
    return null
  }
  const expr =
    vFor && vFor.value && /** @type {VForExpression} */ (vFor.value.expression)
  const variables =
    expr && getUsingIterationVars(slot.value, slot.parent.parent)
  return expr && variables && variables.length > 0 ? { expr, variables } : null
}
Gets the `v-for` directive and variable that provide the variables used by the given `slot` attribute.
@param {VAttribute | VDirective | null} slot The current `slot` attribute node.
@param {VDirective | null} [vFor] The current `v-for` directive node.
@returns { SlotVForVariables | null } The SlotVForVariables.