player entity value may become invalid due to respawns. This not only fixes #633, but also other cases where player reference is used over time while player respawns and its instance is recycled.

src/main/java/carpet/fakes/ServerPlayerEntityInterface.java

@@ -5,4 +5,7 @@ import carpet.helpers.EntityPlayerActionPack;
 public interface ServerPlayerEntityInterface
 {
     EntityPlayerActionPack getActionPack();
+    void invalidateEntityObjectReference();
+    boolean isInvalidEntityObject();
+
 }

src/main/java/carpet/mixins/PlayerManager_scarpetEventsMixin.java

@@ -1,5 +1,6 @@
 package carpet.mixins;
 
+import carpet.fakes.ServerPlayerEntityInterface;
 import net.minecraft.server.PlayerManager;
 import net.minecraft.server.network.ServerPlayerEntity;
 import org.spongepowered.asm.mixin.Mixin;
@@ -17,4 +18,11 @@ public class PlayerManager_scarpetEventsMixin
     {
         PLAYER_RESPAWNS.onPlayerEvent(player);
     }
+
+    @Inject(method = "respawnPlayer", at = @At(value = "INVOKE", target = "Lnet/minecraft/server/network/ServerPlayerEntity;onSpawn()V"))
+    private void invalidatePreviousInstance(ServerPlayerEntity player, boolean alive, CallbackInfoReturnable<ServerPlayerEntity> cir)
+    {
+        ((ServerPlayerEntityInterface)player).invalidateEntityObjectReference();
+    }
+
 }

src/main/java/carpet/mixins/ServerPlayerEntity_scarpetEventMixin.java

@@ -1,6 +1,7 @@
 package carpet.mixins;
 
 import carpet.fakes.EntityInterface;
+import carpet.fakes.ServerPlayerEntityInterface;
 import carpet.script.EntityEventsGroup;
 import com.mojang.authlib.GameProfile;
 import net.minecraft.entity.Entity;
@@ -28,8 +29,11 @@ import static carpet.script.CarpetEventServer.Event.PLAYER_FINISHED_USING_ITEM;
 import static carpet.script.CarpetEventServer.Event.STATISTICS;
 
 @Mixin(ServerPlayerEntity.class)
-public abstract class ServerPlayerEntity_scarpetEventMixin extends PlayerEntity
+public abstract class ServerPlayerEntity_scarpetEventMixin extends PlayerEntity implements ServerPlayerEntityInterface
 {
+    // to denote if the player reference is valid
+
+    private boolean isInvalidReference = false;
 
     public ServerPlayerEntity_scarpetEventMixin(World world, BlockPos blockPos, float f, GameProfile gameProfile)
     {
@@ -109,6 +113,17 @@ public abstract class ServerPlayerEntity_scarpetEventMixin extends PlayerEntity
             }
             PLAYER_CHANGES_DIMENSION.onDimensionChange(player, previousLocation, to, previousDimension, destination.getRegistryKey());
         }
+    };
+
+    @Override
+    public void invalidateEntityObjectReference()
+    {
+        isInvalidReference = true;
     }
 
+    @Override
+    public boolean isInvalidEntityObject()
+    {
+        return isInvalidReference;
+    }
 }

src/main/java/carpet/script/value/EntityValue.java

@@ -7,6 +7,7 @@ import carpet.fakes.LivingEntityInterface;
 import carpet.fakes.MemoryInterface;
 import carpet.fakes.MobEntityInterface;
 import carpet.fakes.HungerManagerInterface;
+import carpet.fakes.ServerPlayerEntityInterface;
 import carpet.fakes.ServerPlayerInteractionManagerInterface;
 import carpet.helpers.Tracer;
 import carpet.network.ServerNetworkHandler;
@@ -90,7 +91,7 @@ import static carpet.utils.MobAI.genericJump;
 // TODO: decide whether copy(entity) should duplicate entity in the world.
 public class EntityValue extends Value
 {
-    private final Entity entity;
+    private Entity entity;
 
     public EntityValue(Entity e)
     {
@@ -119,6 +120,11 @@ public class EntityValue extends Value
 
     public Entity getEntity()
     {
+        if (entity instanceof ServerPlayerEntity && ((ServerPlayerEntityInterface)entity).isInvalidEntityObject())
+        {
+            ServerPlayerEntity newPlayer = entity.getServer().getPlayerManager().getPlayer(entity.getUuid());
+            if (newPlayer != null) entity = newPlayer;
+        }
         return entity;
     }
 
@@ -170,7 +176,7 @@ public class EntityValue extends Value
     @Override
     public String getString()
     {
-        return entity.getName().getString();
+        return getEntity().getName().getString();
     }
 
     @Override
@@ -184,7 +190,7 @@ public class EntityValue extends Value
     {
         if (v instanceof EntityValue)
         {
-            return entity.getEntityId()==((EntityValue) v).entity.getEntityId();
+            return getEntity().getEntityId()==((EntityValue) v).getEntity().getEntityId();
         }
         return super.equals((Value)v);
     }
@@ -220,7 +226,7 @@ public class EntityValue extends Value
     @Override
     public int hashCode()
     {
-        return entity.hashCode();
+        return getEntity().hashCode();
     }
 
     public static EntityClassDescriptor getEntityDescriptor(String who, MinecraftServer server)
@@ -374,7 +380,7 @@ public class EntityValue extends Value
             throw new InternalExpressionException("Unknown entity feature: "+what);
         try
         {
-            return featureAccessors.get(what).apply(entity, arg);
+            return featureAccessors.get(what).apply(getEntity(), arg);
         }
         catch (NullPointerException npe)
         {
@@ -835,7 +841,7 @@ public class EntityValue extends Value
             throw new InternalExpressionException("Unknown entity action: " + what);
         try
         {
-            featureModifiers.get(what).accept(entity, toWhat);
+            featureModifiers.get(what).accept(getEntity(), toWhat);
         }
         catch (NullPointerException npe)
         {
@@ -1468,7 +1474,7 @@ public class EntityValue extends Value
         EntityEventsGroup.Event event = EntityEventsGroup.Event.byName.get(eventName);
         if (event == null)
             throw new InternalExpressionException("Unknown entity event: " + eventName);
-        ((EntityInterface)entity).getEventContainer().addEvent(event, cc.host, fun, args);
+        ((EntityInterface)getEntity()).getEventContainer().addEvent(event, cc.host, fun, args);
     }
 
     @Override
@@ -1477,7 +1483,7 @@ public class EntityValue extends Value
         if (!force) throw new NBTSerializableValue.IncompatibleTypeException(this);
         CompoundTag tag = new CompoundTag();
         tag.put("Data", getEntity().toTag( new CompoundTag()));
-        tag.put("Name", StringTag.of(Registry.ENTITY_TYPE.getId(entity.getType()).toString()));
+        tag.put("Name", StringTag.of(Registry.ENTITY_TYPE.getId(getEntity().getType()).toString()));
         return tag;
     }
 }