Worldgen Modifier Load Conditions

Let's say you wanted to add a rock feature to Terralith's Forested Highlands biome. Your worldgen modifier may look like this:

{
  "type": "lithostitched:add_features",
  "biomes": "terralith:forested_highlands",
  "features": "my_mod:rock",
  "step": "vegetal_decoration"
}

The game will throw an error when loading the pack if Terralith isn't installed because it can't find the terralith:forested_highlands biome. Using load conditions, we can tell the game to simply not load the modifier file if Terralith isn't installed.

Load conditions in 1.20

In 1.20, Fabric doesn't support load conditions for custom files like worldgen modifiers. To bridge that gap, Lithostitched has modifier predicates in this version.

{
  "predicate": {
    "type": "lithostitched:mod_loaded",
    "mod_id": "terralith"
  },
  "type": "lithostitched:add_features",
  "biomes": "terralith:forested_highlands",
  "features": "my_mod:rock",
  "step": "vegetal_decoration"
}

All modifier predicates have a type field, indicating the modifier type to use. Each modifier can add more fields if it needs to.

The built-in modifier types are as follows:

• all_of: All modifier predicates in the predicates list of this modifier predicate must pass for this modifier to pass.
• any_of: At least one of the modifier predicates in the predicates list of this modifier predicate must pass for this modifier to pass.
• not: The modifier predicate in the predicate field of this modifier predicate must fail for this modifier to pass.
• mod_loaded: A mod with the id in the mod_id field must be installed for this modifier to pass.
• true: This modifier predicate always passes.

Load conditions in 1.21

In 1.21, both Fabric and Neoforge support their own load conditions for custom files like worldgen modifiers.

Neoforge has a documentation page on their format, and Fabric has javadocs on their format. If you're building a datapack/mod for both Fabric and Forge, the modifier above can be modified to this to fix it:

{
  "fabric:load_conditions": {
    "condition": "fabric:all_mods_loaded",
    "values": [
      "terralith"
    ]  
  },
  "neoforge:conditions": [
    {
      "type": "neoforge:mod_loaded",
      "modid": "terralith"
    }
  ],
  "type": "lithostitched:add_features",
  "biomes": "terralith:forested_highlands",
  "features": "my_mod:rock",
  "step": "vegetal_decoration"
}