Fixes the structure API for 1.18. (#1730)

Structures are no longer linked to Biomes via an instance field  in the Biome class. Instead they are linked by registry keys. This means that standard biome spawning rules also apply to superflat worlds, instead of the hardcoded list of structures linked with superflat worlds by default. Changes the FabricStructureBuilder to allow adding structures to this default list.

fabric-structure-api-v1/src/main/java/net/fabricmc/fabric/api/structure/v1/FabricStructureBuilder.java

@@ -20,16 +20,14 @@ import java.util.Objects;
 
 import com.google.common.collect.ImmutableList;
 
-import net.minecraft.world.gen.GenerationStep;
 import net.minecraft.util.Identifier;
+import net.minecraft.world.gen.GenerationStep;
 import net.minecraft.world.gen.chunk.StructureConfig;
 import net.minecraft.world.gen.chunk.StructuresConfig;
-import net.minecraft.world.gen.feature.ConfiguredStructureFeature;
 import net.minecraft.world.gen.feature.FeatureConfig;
 import net.minecraft.world.gen.feature.StructureFeature;
 
 import net.fabricmc.fabric.impl.structure.FabricStructureImpl;
-import net.fabricmc.fabric.mixin.structure.FlatChunkGeneratorConfigAccessor;
 import net.fabricmc.fabric.mixin.structure.StructureFeatureAccessor;
 
 /**
@@ -55,7 +53,7 @@ public final class FabricStructureBuilder<FC extends FeatureConfig, S extends St
 	private final S structure;
 	private GenerationStep.Feature step;
 	private StructureConfig defaultConfig;
-	private ConfiguredStructureFeature<FC, ? extends StructureFeature<FC>> superflatFeature;
+	private boolean generateInSuperflat = false;
 	private boolean adjustsSurface = false;
 
 	private FabricStructureBuilder(Identifier id, S structure) {
@@ -66,7 +64,7 @@ public final class FabricStructureBuilder<FC extends FeatureConfig, S extends St
 	/**
 	 * Creates a new {@code FabricStructureBuilder} for registering a structure.
 	 *
-	 * @param id The structure ID.
+	 * @param id        The structure ID.
 	 * @param structure The {@linkplain StructureFeature} you want to register.
 	 */
 	public static <FC extends FeatureConfig, S extends StructureFeature<FC>> FabricStructureBuilder<FC, S> create(Identifier id, S structure) {
@@ -113,11 +111,10 @@ public final class FabricStructureBuilder<FC extends FeatureConfig, S extends St
 	 *
 	 * <p>This is a required option. Vanilla needs it to function.</p>
 	 *
-	 * @param spacing The average distance between 2 structures of this type along the X and Z axes.
+	 * @param spacing    The average distance between 2 structures of this type along the X and Z axes.
 	 * @param separation The minimum distance between 2 structures of this type.
-	 * @param salt The random salt of the structure. This does not affect how common the structure is, but every
+	 * @param salt       The random salt of the structure. This does not affect how common the structure is, but every
-	 *                structure must have an unique {@code salt} in order to spawn in different places.
+	 *                   structure must have an unique {@code salt} in order to spawn in different places.
-	 *
 	 * @see #defaultConfig(StructureConfig)
 	 */
 	public FabricStructureBuilder<FC, S> defaultConfig(int spacing, int separation, int salt) {
@@ -125,27 +122,14 @@ public final class FabricStructureBuilder<FC extends FeatureConfig, S extends St
 	}
 
 	/**
-	 * Sets the structure configuration which spawns in superflat worlds. If unset, this structure will not spawn in
+	 * Enables generation of this feature in superflat worlds. Structures will still only generate in biomes
-	 * superflat worlds.
+	 * for which they have been enabled. Superflat worlds will use the plains biome by default.
-	 *
-	 * @see #superflatFeature(FeatureConfig)
 	 */
-	public FabricStructureBuilder<FC, S> superflatFeature(ConfiguredStructureFeature<FC, ? extends StructureFeature<FC>> superflatFeature) {
+	public FabricStructureBuilder<FC, S> enableSuperflat() {
-		Objects.requireNonNull(superflatFeature, "superflatFeature must not be null");
+		this.generateInSuperflat = true;
-		this.superflatFeature = superflatFeature;
 		return this;
 	}
 
-	/**
-	 * Sets the structure configuration which spawns in superflat worlds. If unset, this structure will not spawn in
-	 * superflat worlds.
-	 *
-	 * @see #superflatFeature(ConfiguredStructureFeature)
-	 */
-	public FabricStructureBuilder<FC, S> superflatFeature(FC config) {
-		return superflatFeature(structure.configure(config));
-	}
-
 	/**
 	 * Causes structure pieces of this structure to adjust the surface of the world to fit them, so that they don't
 	 * stick out of or into the ground.
@@ -174,8 +158,8 @@ public final class FabricStructureBuilder<FC extends FeatureConfig, S extends St
 
 		FabricStructureImpl.STRUCTURE_TO_CONFIG_MAP.put(structure, defaultConfig);
 
-		if (superflatFeature != null) {
+		if (generateInSuperflat) {
-			FlatChunkGeneratorConfigAccessor.getStructureToFeatures().put(structure, superflatFeature);
+			FabricStructureImpl.FLAT_STRUCTURE_TO_CONFIG_MAP.put(structure, defaultConfig);
 		}
 
 		if (adjustsSurface) {

fabric-structure-api-v1/src/main/java/net/fabricmc/fabric/impl/structure/FabricStructureImpl.java

@@ -29,6 +29,9 @@ import net.fabricmc.fabric.api.event.lifecycle.v1.ServerWorldEvents;
 import net.fabricmc.fabric.mixin.structure.StructuresConfigAccessor;
 
 public class FabricStructureImpl implements ModInitializer {
+	//Keeps a map of structures to structure configs for purposes of initializing the flat chunk generator
+	public static final Map<StructureFeature<?>, StructureConfig> FLAT_STRUCTURE_TO_CONFIG_MAP = new HashMap<>();
+
 	//Keeps a map of structures to structure configs.
 	public static final Map<StructureFeature<?>, StructureConfig> STRUCTURE_TO_CONFIG_MAP = new HashMap<>();
 

fabric-structure-api-v1/src/main/java/net/fabricmc/fabric/mixin/structure/FlatChunkGeneratorConfigMixin.java

@@ -16,19 +16,21 @@
 
 package net.fabricmc.fabric.mixin.structure;
 
-import java.util.Map;
-
 import org.spongepowered.asm.mixin.Mixin;
-import org.spongepowered.asm.mixin.gen.Accessor;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
 
 import net.minecraft.world.gen.chunk.FlatChunkGeneratorConfig;
-import net.minecraft.world.gen.feature.ConfiguredStructureFeature;
+import net.minecraft.world.gen.chunk.StructuresConfig;
-import net.minecraft.world.gen.feature.StructureFeature;
+
+import net.fabricmc.fabric.impl.structure.FabricStructureImpl;
 
 @Mixin(FlatChunkGeneratorConfig.class)
-public interface FlatChunkGeneratorConfigAccessor {
+public class FlatChunkGeneratorConfigMixin {
-	@Accessor("STRUCTURE_TO_FEATURES")
+	@Inject(method = "getDefaultConfig", at = @At(value = "RETURN"))
-	static Map<StructureFeature<?>, ConfiguredStructureFeature<?, ?>> getStructureToFeatures() {
+	private static void createDefaultConfig(CallbackInfoReturnable<FlatChunkGeneratorConfig> cir) {
-		throw new AssertionError("Untransformed accessor");
+		StructuresConfig structuresConfig = cir.getReturnValue().getStructuresConfig();
+		structuresConfig.getStructures().putAll(FabricStructureImpl.FLAT_STRUCTURE_TO_CONFIG_MAP);
 	}
 }

fabric-structure-api-v1/src/main/resources/fabric-structure-api-v1.mixins.json

@@ -4,7 +4,7 @@
   "compatibilityLevel": "JAVA_16",
   "mixins": [
     "ChunkSerializerMixin",
-    "FlatChunkGeneratorConfigAccessor",
+    "FlatChunkGeneratorConfigMixin",
     "StructureFeatureAccessor",
     "StructuresConfigAccessor"
   ],

fabric-structure-api-v1/src/testmod/java/net/fabricmc/fabric/test/structure/StructureTest.java

@@ -61,7 +61,7 @@ public class StructureTest {
 		FabricStructureBuilder.create(new Identifier("fabric", "test_structure"), STRUCTURE)
 				.step(GenerationStep.Feature.SURFACE_STRUCTURES)
 				.defaultConfig(32, 8, 12345)
-				.superflatFeature(CONFIGURED_STRUCTURE)
+				.enableSuperflat()
 				.adjustsSurface()
 				.register();
 		Registry.register(Registry.STRUCTURE_PIECE, new Identifier("fabric", "test_structure_piece"), PIECE);

fabric-structure-api-v1/src/testmod/java/net/fabricmc/fabric/test/structure/mixin/MixinConfiguredStructureFeatures.java

@@ -33,7 +33,7 @@ import net.fabricmc.fabric.test.structure.StructureTest;
 
 @Mixin(ConfiguredStructureFeatures.class)
 public class MixinConfiguredStructureFeatures {
-	@Inject(method = "method_38571", at = @At("TAIL"))
+	@Inject(method = "method_38570", at = @At("TAIL"))
 	private static void addStructuresToBiomes(BiConsumer<ConfiguredStructureFeature<?, ?>, RegistryKey<Biome>> consumer, CallbackInfo ci) {
 		consumer.accept(StructureTest.CONFIGURED_STRUCTURE, BiomeKeys.PLAINS);
 	}