Ancient City Maps Trade

A tiny standalone mod for Minecraft Forge 1.20.1 that adds a Cartographer villager trade for a treasure map leading to the nearest Ancient City — the same mechanic vanilla already uses for ocean monuments and woodland mansions, just extended to a structure vanilla itself doesn't offer a map for.

What it does

• Adds one Cartographer trade (level 4): 16 emeralds + a compass → an Ancient City Explorer Map.
• The map is generated live from the actual findNearestMapStructure lookup — same underlying mechanism as vanilla's Ocean/Woodland Explorer Maps, not a fixed/precomputed location.
• Ships its own structure tag (on_ancient_city_explorer_maps, containing minecraft:ancient_city) since vanilla has no tag covering it.
• No new items, blocks, or recipes — the only thing this mod adds is the trade itself.

Vanilla's own VillagerTrades.TreasureMapForEmeralds (the class doing this for monuments/mansions) turned out to be package-private, so this reimplements VillagerTrades.ItemListing directly, with the map-generation logic ported from vanilla's own bytecode rather than guessed.

Dependencies

None beyond Minecraft Forge 1.20.1-47.4.10+. No other mod required.