Suppose that I have a single empty supply pile. If I play Poacher, I will have to discard a card from my hand. If I discard a Tunnel, I can reveal it to gain a gold.
Question: If I do so and thereby empty the gold pile, will I need to discard another card for the Poacher?
When is the number of empty supply piles evaluated? Only once before I start discarding, or again after each discarding?