datagen.java

private static void oilLakeDatagen(GatherDataEvent event, DataGenerator generator, ExistingFileHelper existingFileHelper, RegistryOps<JsonElement> registryOps) {
        // oil lake configured feature
        ConfiguredFeature<?,?> oilLakeCF = new ConfiguredFeature<>(
                Feature.LAKE,
                new LakeFeature.Configuration(
                        BlockStateProvider.simple(ModBlocks.OIL.get().defaultBlockState()),
                        BlockStateProvider.simple(Blocks.AIR.defaultBlockState())
                )
        );
        JsonCodecProvider<ConfiguredFeature<?,?>> cfProvider = JsonCodecProvider.forDatapackRegistry(
                generator, existingFileHelper, Names.MOD_ID, registryOps, Registry.CONFIGURED_FEATURE_REGISTRY, Map.of(
                        OIL_LAKE_RL, oilLakeCF
                )
        );
        generator.addProvider(event.includeServer(), cfProvider);

        // surface & underground oil lake placed features
        var oilLakeKey = ResourceKey.create(Registry.CONFIGURED_FEATURE_REGISTRY, OIL_LAKE_RL);
        var oilLakeHolder = registryOps.registry(Registry.CONFIGURED_FEATURE_REGISTRY).orElseThrow().getOrCreateHolderOrThrow(oilLakeKey);
        PlacedFeature oilLakeSurface = new PlacedFeature(oilLakeHolder, ImmutableList.of(
                RarityFilter.onAverageOnceEvery(25),
                InSquarePlacement.spread(),
                PlacementUtils.HEIGHTMAP_WORLD_SURFACE,
                BiomeFilter.biome())
        );
        PlacedFeature oilLakeUnderground = new PlacedFeature(oilLakeHolder, ImmutableList.of(
                RarityFilter.onAverageOnceEvery(6),
                InSquarePlacement.spread(),
                HeightRangePlacement.of(UniformHeight.of(VerticalAnchor.absolute(0), VerticalAnchor.top())),
                EnvironmentScanPlacement.scanningFor(Direction.DOWN, BlockPredicate.allOf(
                                BlockPredicate.not(BlockPredicate.ONLY_IN_AIR_PREDICATE),
                                BlockPredicate.insideWorld(new BlockPos(0, -5, 0))
                        ), 32
                ),
                SurfaceRelativeThresholdFilter.of(Heightmap.Types.OCEAN_FLOOR_WG, Integer.MIN_VALUE, -5),
                BiomeFilter.biome())
        );
        JsonCodecProvider<PlacedFeature> pfProvider = JsonCodecProvider.forDatapackRegistry(
                generator, existingFileHelper, Names.MOD_ID, registryOps, Registry.PLACED_FEATURE_REGISTRY, Map.of(
                        OIL_LAKE_SURFACE_RL, oilLakeSurface,
                        OIL_LAKE_UNDERGROUND_RL, oilLakeUnderground
                )
        );
        generator.addProvider(event.includeServer(), pfProvider);

        // biome modifiers
        ResourceKey<PlacedFeature> oilLakeSurfaceKey = ResourceKey.create(Registry.PLACED_FEATURE_REGISTRY, OIL_LAKE_SURFACE_RL);
        BiomeModifier surfaceModifier = new ForgeBiomeModifiers.AddFeaturesBiomeModifier(
                registryOps.registry(Registry.BIOME_REGISTRY).orElseThrow().getOrCreateTag(BiomeTags.IS_OVERWORLD),
                HolderSet.direct(registryOps.registry(Registry.PLACED_FEATURE_REGISTRY).orElseThrow().getOrCreateHolderOrThrow(oilLakeSurfaceKey)),
                GenerationStep.Decoration.LAKES
        );
        ResourceKey<PlacedFeature> oilLakeUndergroundKey = ResourceKey.create(Registry.PLACED_FEATURE_REGISTRY, OIL_LAKE_SURFACE_RL);
        BiomeModifier undergroundModifier = new ForgeBiomeModifiers.AddFeaturesBiomeModifier(
                registryOps.registry(Registry.BIOME_REGISTRY).orElseThrow().getOrCreateTag(BiomeTags.IS_OVERWORLD),
                HolderSet.direct(registryOps.registry(Registry.PLACED_FEATURE_REGISTRY).orElseThrow().getOrCreateHolderOrThrow(oilLakeUndergroundKey)),
                GenerationStep.Decoration.LAKES
        );
        JsonCodecProvider<BiomeModifier> bmProvider = JsonCodecProvider.forDatapackRegistry(
                generator, existingFileHelper, Names.MOD_ID, registryOps, ForgeRegistries.Keys.BIOME_MODIFIERS, Map.of(
                        OIL_LAKE_SURFACE_RL, surfaceModifier,
                        OIL_LAKE_UNDERGROUND_RL, undergroundModifier
                )
        );
        generator.addProvider(event.includeServer(), bmProvider);
    }