When cooking on Yomtov for Shabbos (allowed with the eiruv tavshilin) may one also cook for a gentile guest that he will be having at the Shabbos meal?
Even though one cannot cook on Yomtov for a gentile, if the halacha is according to the opinion that the needs of Shabbos are permitted to be done on Yomtov, but the Chachomim required an eiruv tavshilin to do so, should the gentile guest be considered included in the category of "needs of Shabbos" by using the heter of ribui bishiurim or not?
And if the reason for being able to cook on Yomtov for Shabbos is in accordance with the opinion that we say since you may get guests on Yomtov and it is permissible to cook for them to eat on Yomtov, you may cook for Shabbos based on that possibility that the food may be needed for Yomtov, and the Chachomim required an eiruv tavshilin for this, do we say that this reasoning only applies to cooking for Jews, since it is only permissible to cook for Jews on Yomtov, or could we say that this reasoning, combined with using the heter of ribui bishiurim allows any act of cooking, no matter that you intend for some of it to be for your gentile Shabbos guest?
For clarity's sake, let me add what I already wrote as a comment:
My question is about actually increasing quantity on yomtov for a gentile who will be eating at your house that shabbos, based on eruv tavshilin. Increasing quantity is allowed on Yomtov for one day to the next as long as not specifically stated since it involves the same action as the one you would have done had you not increased the quantity. Could one do so for the sake of his gentile Shabbos guest?