function getVSlotVForVariableIfUsingIterationVars(vSlot, vFor) {
  const expr =
    vFor && vFor.value && /** @type {VForExpression} */ (vFor.value.expression)
  const variables =
    expr && getUsingIterationVars(vSlot.key.argument, vSlot.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` v-slot` directive.
@param {VDirective} vSlot The current `v-slot` directive node.
@param {VDirective | null} [vFor] The current `v-for` directive node.
@returns { VSlotVForVariables | null } The VSlotVForVariable.