Crash at the world creation screen with datapack content added through the Biome API

The game crashes when trying to create a world, if a mod with datapack content that is added through the Biome API is installed. As a clear example, Promenade features Nether and End biomes and features that are now added by the mod’s datapack (see commit https://github.com/DawnTeamMC/Promenade/commit/0e14663a8093a43ce420ed3f0958c8d13bbca925 and this crash log) and then added to vanilla generation through the Biome API, which is part of the Fabric API.

In vanilla Minecraft, when you try to create a world, the vanilla builtin worldgen gets loaded, and then opens the screen with the loaded generic content. However the Biome API lets us add to the vanilla generation by adding RegistryKeys, but actually requires these keys to represent built-in content so that it gets loaded on this specific screen. This constraint should not exist, and as a fix the Fabric API must tell the game to load the mod datapacks at the same time as builtin Minecraft worldgen content on this screen.

[Hugman76]

The issue is still present in 1.19 too

[apple502j]

#2321 backports the fix.