Throne Room: "Choose any action in your hand and play it twice"
Feast: "Trash this card and gain a card costing up to 5$"
So I use the Throne Room and play Feast twice. The first time it gets played it gets trashed and I gain a card up to five. The second time its played the Feast card is in the trash, and to play a Feast it needs to get trashed to gain a card.
I recall the rules say something like when you play an action you must follow as many of the rules as you can, so I assume you would just trash the one Feast and gain 2 cards up to 5$. Is this correct?