MapCodec<A>/Codec<A> (in 1.18)

very_complex.md

public static final MapCodec<MultiNoiseBiomeSource> DIRECT_CODEC = RecordCodecBuilder.mapCodec(
  (instance) -> instance.group(
    RecordCodecBuilder.create(
      (instancex) -> instancex.group(
        Climate.ParameterPoint.CODEC.fieldOf("parameters").forGetter(Pair::getFirst),
        Biome.CODEC.fieldOf("biome").forGetter(Pair::getSecond)
      ).apply(instancex, Pair::of)
    )
    .listOf()
    .xmap(Climate.ParameterList::new, Climate.ParameterList::biomes)
    .fieldOf("biomes")
    .forGetter((multiNoiseBiomeSource) -> multiNoiseBiomeSource.parameters)
  ).apply(instance, MultiNoiseBiomeSource::new)
);

becomes:

public static final MapCodec<MultiNoiseBiomeSource> DIRECT_CODEC = RecordCodecBuilder.mapCodec(
  (instance) -> instance.group(
    RecordCodecBuilder.<Pair<Climate.ParameterPoint, Supplier<Biome>>>create(
      (instancex) -> instancex.group(
        Climate.ParameterPoint.CODEC.fieldOf("parameters").forGetter(Pair<Climate.ParameterPoint, Supplier<Biome>>::getFirst),
        Biome.CODEC.fieldOf("biome").forGetter(Pair<Climate.ParameterPoint, Supplier<Biome>>::getSecond)
      ).apply(instancex, Pair::of)
    )
    .listOf()
    .xmap(Climate.ParameterList::new, Climate.ParameterList::biomes)
    .fieldOf("biomes")
    .forGetter((multiNoiseBiomeSource) -> multiNoiseBiomeSource.parameters)
  ).apply(instance, MultiNoiseBiomeSource::new)
);

private final List<Pair<Biome.ClimateParameters, Supplier<Biome>>> parameters;

Brought type parameters from Pair<F, S> inside parameters field, and added them.

---

public static final MapCodec<MultiNoiseBiomeSource.PresetInstance> CODEC = RecordCodecBuilder.mapCodec((instance) -> instance.group(ResourceLocation.CODEC.flatXmap((resourceLocation) -> (DataResult)Optional.ofNullable(MultiNoiseBiomeSource.Preset.BY_NAME.get(resourceLocation)).map(DataResult::success).orElseGet(() -> DataResult.error("Unknown preset: " + resourceLocation)), (preset) -> DataResult.success(preset.name)).fieldOf("preset").stable().forGetter(MultiNoiseBiomeSource.PresetInstance::preset), RegistryLookupCodec.create(Registry.BIOME_REGISTRY).forGetter(MultiNoiseBiomeSource.PresetInstance::biomes), Codec.LONG.fieldOf("seed").stable().forGetter(MultiNoiseBiomeSource.PresetInstance::seed)).apply(instance, instance.stable(MultiNoiseBiomeSource.PresetInstance::new)));

becomes:

public static final MapCodec<MultiNoiseBiomeSource.PresetInstance> CODEC = RecordCodecBuilder.mapCodec((instance) -> instance.group(ResourceLocation.CODEC.flatXmap((resourceLocation) -> Optional.ofNullable(MultiNoiseBiomeSource.Preset.BY_NAME.get(resourceLocation)).map(DataResult::success).orElseGet(() -> DataResult.error("Unknown preset: " + resourceLocation)), (preset) -> DataResult.success(preset.name)).fieldOf("preset").stable().forGetter(MultiNoiseBiomeSource.PresetInstance::preset), RegistryLookupCodec.create(Registry.BIOME_REGISTRY).forGetter(MultiNoiseBiomeSource.PresetInstance::biomes), Codec.LONG.fieldOf("seed").stable().forGetter(MultiNoiseBiomeSource.PresetInstance::seed)).apply(instance, instance.stable(MultiNoiseBiomeSource.PresetInstance::new)));

Just removed (DataResult) cast (a cast without type parameter).