Prevent sculk events in addPassenger from deadlocking the game during worldgen

This seems to be a vanilla bug when spawning entities that ride other entities

Related: #510

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/common/mixin/bugfix/chunk_deadlock/EntityMixin.java

@@ -0,0 +1,31 @@
+package org.embeddedt.modernfix.common.mixin.bugfix.chunk_deadlock;
+
+import com.llamalad7.mixinextras.injector.v2.WrapWithCondition;
+import com.llamalad7.mixinextras.injector.wrapoperation.WrapOperation;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.level.gameevent.GameEvent;
+import org.embeddedt.modernfix.ModernFix;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+
+@Mixin(Entity.class)
+public class EntityMixin {
+    /**
+     * @author embeddedt
+     * @reason When an entity is added to the world via the worldgen load path (ChunkMap#postLoadProtoChunk calling
+     * ServerLevel#addWorldGenChunkEntities), attempts to add a passenger result in a deadlock when the sculk event
+     * tries to raytrace blocks. To fix this, we skip firing the sculk event if the chunk the entity is within is not
+     * loaded.
+     */
+    @WrapWithCondition(method = "addPassenger", at = @At(value = "INVOKE", target = "Lnet/minecraft/world/entity/Entity;gameEvent(Lnet/minecraft/world/level/gameevent/GameEvent;Lnet/minecraft/world/entity/Entity;)V"))
+    private boolean onlyAddIfSelfChunkLoaded(Entity instance, GameEvent event, Entity entity) {
+        var chunkPos = instance.chunkPosition();
+        if (instance.level() instanceof ServerLevel serverLevel && serverLevel.getChunkSource().getChunkNow(chunkPos.x, chunkPos.z) == null) {
+            ModernFix.LOGGER.warn("Skipped emitting ENTITY_MOUNT game event for entity {} as it would cause deadlock", instance.toString());
+            return false;
+        } else {
+            return true;
+        }
+    }
+}