Gemara

(Beraisa - R. Meir): If one cooked on Shabbos b'Shogeg, he may eat it. If he was Mezid, he may not eat it;

R. Yehudah says, if he was Shogeg, he may eat it after Shabbos. If he was Mezid, he may never eat it;

R. Yochanan ha'Sandlar says, if he was Shogeg, after Shabbos others may eat it but not him. If he was Mezid, even others may never eat it.

R. Yochanan ha'Sandlar expounds like R. Chiya. "Shabbos... is Kodesh to you" - just like one may not eat Kodesh, one may not eat Ma'ase (something made on) Shabbos.

Suggestion: Perhaps the Isur applies even to things done b'Shogeg!

Rejection: "Those who desecrate it will die" - the verse discusses only Mezid.

Rav Acha and Ravina argued about whether the Isur to benefit from Ma'ase Shabbos is mid'Oraisa or mid'Rabanan.

The one who says that it is mid'Oraisa learns like above.

The one who says that it is mid'Rabanan expounds "It (Shabbos) is Kodesh", but Ma'ase Shabbos is not.

Shabbos 38a (R. Chiya bar Aba): If one cooks on Shabbos:

If he was Shogeg, he may eat the food; if he was Mezid, he may not eat it (if this is like R. Meir, he discusses eating the food on Shabbos; if it is like R. Yehudah, he discusses eating it after Shabbos).

(Rav Yehudah bar Shmuel): At first, the Halachah was that if one cooked on Shabbos, he may eat it. If he was Mezid, he may not eat it. The same applies to one who was Meshaheh;

Many people did Shehiyah b'Mezid and said that they were Shogeg. Chachamim decreed that even if one was b'Shogeg it is forbidden.

Chulin 15a (Rav Chanan bar Ami): Rav would rule to his Talmidim like R. Meir. In public he ruled like R. Yehudah, due to ignoramuses.

Rishonim

Rif and Rosh (Shabbos 17a and Chulin 1:18) bring our Gemara.

Rif (also brought in Rosh, ibid.): Whenever Rav Acha and Ravina argue, the Halachah follows the lenient opinion. This shows that the Halachah does not follow R. Yochanan ha'Sandlar. Therefore, the Halachah follows R. Yehudah, who says that if he was Shogeg, he or others may eat it after Shabbos. If he was Mezid, others may eat it after Shabbos, but he may not.

Rebuttal (Ba'al ha'Ma'or): The Gemara in Kesuvos and Bava Kama explicitly says that Rav Acha and Ravina discuss whether R. Yochanan ha'Sandlar forbids Meleches Shabbos mid'Oraisa or mid'Rabanan! This is no source that the Halachah does not follow R. Yochanan ha'Sandlar! Rather, we rely on Rav, who would rule to his Talmidim like R. Meir, but in public he ruled like R. Yehudah, due to ignoramuses.

Defense #1 (Milchamos Hash-m): We hold like the more lenient one of Rav Acha and Ravina, that Meleches Shabbos is permitted mid'Oraisa. This is unlike R. Yochanan ha'Sandlar! Therefore, we rely on the rule that the Halachah follows R. Yehudah against R. Meir. Since we hold that Meleches Shabbos is mid'Rabanan, surely we are not so stringent like R. Yochanan ha'Sandlar. We cannot learn from Rav, who holds that the rules of Pesak (Eruvin 47a) only teach which Tana'im we are inclined to follow. We hold that the rules teach whom the Halachah follows, so we rule like R. Yehudah to everyone. Nowadays there are few discreet Talmidim, so in any case we must rule like R. Yehudah. The Rif is often concerned for ignoramuses. Also, Rav himself established our Stam Mishnah to be R. Yehudah. R. Chiya, Abaye and Rav Papi did not eat foods prepared on Shabbos by (respectively) his Rebbi's wife, his (surrogate) mother, and the household of Rabah bar Shmuel, even though none of them were suspected to transgress b'Mezid.

Rebuttal (Gra OC 318:1 DH ha'Mevashel): The proof for Tosfos (and the Ba'al ha'Ma'or) is solid. The Mishnah in Chulin like R. Yehudah is not decisive, for the Mishnah in Terumos is like R. Meir. The Sugya in Shabbos (38a) and Rav rule like R. Meir. The Ramban's text should say that we do not rely on Rav, who argues with the rules (of Pesak), rather, like R. Yochanan (who taught them). However, elsewhere the Rif and Poskim rule like R. Shimon (against the rules) because Rav rules like him! Rather, we do not rely on the rules when there is an explicit Pesak against them. Further, an argument in a Beraisa does not override a Stam Mishnah. We do not rely on a Diyuk that the Mishnah in Chulin is like R. Yehudah, against a Mishnah explicitly like R. Meir. All the Ramban's proofs from Amora'im who did not eat prove that we follow R. Meir! All were cases of Isurim mid'Rabanan. R. Meir fines when an Isur mid'Rabanan was done, and R. Yehudah does not.

Defense #2 (of Rif - Gra, ibid.): In the Yerushalmi, R. Yochanan established a different Stam Mishnah in Terumos like R. Yehudah. Perhaps R. Yochanan favors that Stam Mishnah because we follow R. Yehudah against R. Meir. Rav does not, for he disagrees with the rules of Pesak. The only Hava Amina to rule like R. Yochanan ha'Sandlar was because the Gemara (Bava Kama 71a) established Chachamim like him. Since we rule like the lenient opinion of Rav Acha and Ravina that Meleches Shabbos is forbidden mid'Rabanan, we cannot say that Chachamim hold like R. Yochanan ha'Sandlar.

Conclusion (Gra): In the Yerushalmi, a case occurred and R. Tzadok refused to eat R. Gamliel's food because he thought that the peppers were crushed on Yom Tov. It asked why he did not eat, since the Isur was Shogeg. It said that he did not want to permit Melachah through R. Gamliel. This shows that letter of the law, it is permitted. The Ramban does not rely on this, for the Bavli did not bring it. This is wrong. We do not spurn an explicit proof from the Yerushalmi. In the Yerushalmi, R. Yochanan permits Shogeg whether an Isur mid'Rabanan or mid'Oraisa was done. Tosfos (Beitzah 6a DH ve'Ha'idna) learns from food cooked by Nochrim that we are considered Bnei Torah.

Ran (DH Garsinan): If one cooked on Shabbos b'Shogeg, R. Meir permits even him to eat it, even on Shabbos. If he was Mezid, R. Meir forbids even others to eat it on Shabbos, but even he may eat it after Shabbos. R. Meir did not explicitly teach the law about others, for parallel structure with the Reisha, which discusses only him. R. Yehudah says, if he was Shogeg, even he may eat it after Shabbos. This is like R. Meir says about Mezid. If he was Mezid, he may never eat it; after Shabbos others may eat it. This is like R. Yochanan ha'Sandlar says about Shogeg.

Rashi (Chulin 15a): No one may benefit from Meleches Shabbos, i.e. what was done b'Mezid. R. Yehudah forbids on Shabbos even when the Melachah was b'Shogeg, for this is benefit from an Aveirah. We cannot say that he decrees Shogeg due to Mezid, for if so the Mevashel would never be permitted. R. Yochanan ha'Sandlar decrees Shogeg due to Mezid, and forbids the Mevashel permanently.

Rosh (ibid.): The Ri says that the Halachah follows R. Meir. He brings a proof from Rav, who would rule to his Talmidim like R. Meir, but in public he ruled like R. Yehudah, due to ignoramuses. This shows that he holds like R. Meir, just he was concerned lest ignoramuses belittle Shabbos. In Shabbos, R. Chiya bar Aba permits one who cooked on Shabbos b'Shogeg to eat the food, but not one who was Mezid. The Ge'onim say that nowadays we expound in public to ignorant people, so we rule like R. Yehudah.

Rambam (Hilchos Shabbos 6:23): If a Yisrael cooked on Shabbos b'Mezid, others may eat it after Shabbos, but he may never eat it. If he was Shogeg, he or others may eat it immediately after Shabbos.

Poskim

Shulchan Aruch (OC 318:1): If one cooked on Shabbos b'Mezid, he may never eat it, but others may eat it immediately after Shabbos. If he was Shogeg, it is forbidden on Shabbos also to others. After Shabbos it is permitted also to him immediately.

Beis Yosef (DH ul'Inyan): Tosfos, SMaG and Sefer ha'Terumos rule like R. Meir, like Rav (to his Talmidim) and Rava (it seems that this should say R. Chiya bar Aba - Shabbos 38a). However, SMaG says that nowadays we rule like R. Yehudah due to ignoramuses.