Indeed, the json was easier to find that expected – I wasted time looking in the actual CODE and couldn’t find it.
Anyway –
I’ve left out most of the things that aren’t strictly edible. It’s possible I missed something, there are a lot more than I thought there were. Spoilers ahead, blah blah, etc.
blackjack, willow, pine, birch basically all year round, though I believe willows die in the winter?
Spring - Apparently nothing
Summer - Elderberry, mulberry, plum, apricot, peach, cherry, grape, raspberry, huckleberry, blackberry, strawberry, blueberry.
Autumn - Pecan, almond, pistachio, hickory, coffee, pear, apple, hazelnut, beech, chestnut, walnut, peanut.
Winter - Also apparently nothing.
This information appears in terrain.json. If you’re running mods that add harvestable trees/bushes, they’ll probably be listed with the other terrain for consistency’s sake.