EATING ON EREV SHABBOS AND YOM TOV [Erev:Shabbos:Yom Tov:eating]
R. Yehudah forbids eating on Erev Shabbos or Yom Tov from shortly before Minchah;
R. Yosi permits until dark.
100a - R. Yehudah: If one was eating and Shabbos came, he must interrupt (remove the table and say Birkas ha'Mazon);
R. Yosi: He need not interrupt.
Gitin 38b - R. Chiya bar Aba: There was a family in Yerushalayim that used to fix a (big) meal on Erev Shabbos - it was uprooted.
Rif and Rosh (10:2): One may eat until dark
Source: The Halachah follows R. Yosi against any colleague.
Rambam (Hilchos Shabbos 30:4): One may eat and drink until dark. However, one may not fix a meal and Mishteh (drinking repast) on Erev Shabbos.
Source - Magid Mishnah: He learns the Isur from the family that was uprooted (Gitin 38B).
Rambam (ibid.): It is a Mitzvah to enter Shabbos with appetite.
Source - Gra (DH Aval): We learn the Mitzvah from 100a. Tana'im argue about interrupting, but no one permits l'Chatchilah to eat until Shabbos enters.
Shulchan Aruch (OC 249:2): On Erev Shabbos, even in the morning, one may not fix a meal and Mishteh bigger than he eats during the week. This is so he will enter Shabbos with appetite.
Taz (1): It is forbidden only to fix a meal and Mishteh, lest he get drunk.
Magen Avraham (4): R. Tam explains that a big meal is forbidden lest one be busy with the meal and not prepare for Shabbos.
Kaf ha'Chayim (11): R. Tam permits a big meal to one who has others to prepare Shabbos for him; the Shulchan Aruch forbids, lest he enter Shabbos sated.
Shulchan Aruch (ibid.): Even Seudas Kidushin is forbidden.
Rema: A Seudas Mitzvah whose time is fixed, e.g. of Bris Milah or Pidyon ha'Ben, is permitted.
Pri Megadim (3): If Kidushin or Nisu'in was on Erev Shabbos, one may make the Seudah that day. Even though we are more stringent about eating on Erev Pesach, the Mishnah (49A) considers Seudas Kidushin on Erev Pesach to be a Mitzvah! Nevertheless, it is better to make the Seudah on another day.
Shulchan Aruch (ibid.): If one does not fix a meal, he may eat the amount of a normal weekday meal any time during the day. Even fixing a normal meal is not forbidden. However, it is a Mitzvah to refrain after nine hours in order to enter Shabbos with appetite.
Source - Beis Yosef (DH Ein Kov'in): Our Mishnah teaches that if one refrains from then he will have appetite at night.
Gra (DH v'Le'echol): In the Mishnah R. Yosi discusses eating without fixing a meal.
Darchei Moshe ha'Aruch: Or Zaru'a forbids eating Mezonos on Shabbos before the meal, for one should have appetite for the primary meal with bread. However, we hold that one may eat on Erev Shabbos after Minchah, i.e. one need not enter with appetite, therefore it is permitted.
Rebuttal (Magen Avraham 6): We could hold like Or Zaru'a! Perhaps eating on Shabbos itself is more stringent than on Erev Shabbos. Also, the Mezonos should be eaten in the meal to avoid unnecessary Berachos.
Mishnah Berurah (8,13,17): The Isur to fix a big meal also applies to Erev Yom Tov, for it is also a Mitzvah to honor Yom Tov. When a large meal is permitted, it is better to make it in the morning. In winter, nine (relative) hours of the day is less than three (60-minute) hours before night; one should not begin even before this if it will curb his appetite at night.