Fix mob entity inventory loss when switching dimensions

The inventory was being cleared by removing the entity
from the world, but Folia changed the remove to be
before the entity copy which caused the new entity
to have a cleared inventory. Fix this by creating
a post-dimension copy callback that will clear
the inventory of the old entity.

Fixes https://github.com/PaperMC/Folia/issues/29

patches/server/0005-Threaded-Regions.patch

@@ -17927,7 +17927,7 @@ index 93a1e990b0a6caae4143c2f9d09bfb368fa1d6db..ad3166481dd37f4b5380f8bf28653bb4
  
                  itemstack = entityliving2.getMainHandItem();
 diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
-index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278e4a4b091 100644
+index 4705d7066207250c03a5f98eef61554c901f2e35..580e75595d7fc8c5af5a0281b77f7be88a25a464 100644
 --- a/src/main/java/net/minecraft/world/entity/Entity.java
 +++ b/src/main/java/net/minecraft/world/entity/Entity.java
 @@ -165,7 +165,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
@@ -18110,7 +18110,7 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
              return;
          }
          // CraftBukkit end
-@@ -3380,6 +3406,751 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -3380,6 +3406,754 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
          this.portalEntrancePos = original.portalEntrancePos;
      }
  
@@ -18399,6 +18399,9 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
 +        Entity copy = this.getType().create(destination);
 +        copy.restoreFrom(this);
 +        copy.transform(pos, yaw, pitch, speedDirectionUpdate);
++        // vanilla code used to call remove _after_ copying, and some stuff is required to be after copy - so add hook here
++        // for example, clearing of inventory after switching dimensions
++        this.postRemoveAfterChangingDimensions();
 +
 +        return copy;
 +    }
@@ -18862,7 +18865,7 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
      @Nullable
      public Entity changeDimension(ServerLevel destination) {
          // CraftBukkit start
-@@ -3388,6 +4159,11 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -3388,6 +4162,11 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
  
      @Nullable
      public Entity teleportTo(ServerLevel worldserver, PositionImpl location) {
@@ -18874,7 +18877,20 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
          // CraftBukkit end
          // Paper start - fix bad state entities causing dupes
          if (!isAlive() || !valid) {
-@@ -3910,17 +4686,13 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -3471,6 +4250,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+         }
+     }
+ 
++    // Folia start - region threading - move inventory clearing until after the dimension change
++    protected void postRemoveAfterChangingDimensions() {
++
++    }
++    // Folia end - region threading - move inventory clearing until after the dimension change
++
+     protected void removeAfterChangingDimensions() {
+         this.setRemoved(Entity.RemovalReason.CHANGED_DIMENSION);
+     }
+@@ -3910,17 +4695,13 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
  
      // Paper start
      public void startSeenByPlayer(ServerPlayer player) {
@@ -18894,7 +18910,7 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
      }
      // Paper end
  
-@@ -4411,7 +5183,8 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -4411,7 +5192,8 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
              }
          }
          // Paper end - fix MC-4
@@ -18904,7 +18920,7 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
              synchronized (this.posLock) { // Paper
              this.position = new Vec3(x, y, z);
              } // Paper
-@@ -4432,7 +5205,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -4432,7 +5214,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
  
          // Paper start - never allow AABB to become desynced from position
          // hanging has its own special logic
@@ -18913,7 +18929,7 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
              this.setBoundingBox(this.makeBoundingBox());
          }
          // Paper end
-@@ -4519,6 +5292,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -4519,6 +5301,12 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
          return this.removalReason != null;
      }
  
@@ -18926,7 +18942,7 @@ index 4705d7066207250c03a5f98eef61554c901f2e35..f2d5603c6d0b3f7aa4b8f8da2c551278
      @Nullable
      public Entity.RemovalReason getRemovalReason() {
          return this.removalReason;
-@@ -4543,7 +5322,23 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
+@@ -4543,7 +5331,23 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
  
          if (reason != RemovalReason.UNLOADED_TO_CHUNK) this.getPassengers().forEach(Entity::stopRiding); // Paper - chunk system - don't adjust passenger state when unloading, it's just not safe (and messes with our logic in entity chunk unload)
          this.levelCallback.onRemove(reason);
@@ -19029,7 +19045,7 @@ index dcfb71b5a53df789e366fea2080921d677549a2e..4f8062432cfe6480664e674fde0255f0
  
              while (!flag2 && blockposition.getY() > world.getMinBuildHeight()) {
 diff --git a/src/main/java/net/minecraft/world/entity/Mob.java b/src/main/java/net/minecraft/world/entity/Mob.java
-index 02cb6b8c1d59855ff4a8aad3024fe12007eca0ee..88e2d818264450e63e0f5693fdc7940d072e50a6 100644
+index 02cb6b8c1d59855ff4a8aad3024fe12007eca0ee..a719dc69b48ae867ce0b508d3d640e65d2863068 100644
 --- a/src/main/java/net/minecraft/world/entity/Mob.java
 +++ b/src/main/java/net/minecraft/world/entity/Mob.java
 @@ -135,6 +135,14 @@ public abstract class Mob extends LivingEntity implements Targeting {
@@ -19092,6 +19108,33 @@ index 02cb6b8c1d59855ff4a8aad3024fe12007eca0ee..88e2d818264450e63e0f5693fdc7940d
  
              if (entityhuman != null) {
                  double d0 = entityhuman.distanceToSqr((Entity) this);
+@@ -1728,6 +1743,15 @@ public abstract class Mob extends LivingEntity implements Targeting {
+         this.goalSelector.removeAllGoals(predicate);
+     }
+ 
++    // Folia start - region threading - move inventory clearing until after the dimension change
++    @Override
++    protected void postRemoveAfterChangingDimensions() {
++        this.getAllSlots().forEach((itemstack) -> {
++            if (!itemstack.isEmpty()) itemstack.setCount(0); // CraftBukkit
++        });
++    }
++    // Folia end - region threading - move inventory clearing until after the dimension change
++
+     @Override
+     protected void removeAfterChangingDimensions() {
+         super.removeAfterChangingDimensions();
+@@ -1736,9 +1760,7 @@ public abstract class Mob extends LivingEntity implements Targeting {
+         this.level.getCraftServer().getPluginManager().callEvent(event); // CraftBukkit
+         this.dropLeash(true, event.isDropLeash());
+         // Paper end
+-        this.getAllSlots().forEach((itemstack) -> {
+-            if (!itemstack.isEmpty()) itemstack.setCount(0); // CraftBukkit
+-        });
++        // Folia - region threading - move inventory clearing until after the dimension change - move into postRemoveAfterChangingDimensions
+     }
+ 
+     @Nullable
 diff --git a/src/main/java/net/minecraft/world/entity/ai/Brain.java b/src/main/java/net/minecraft/world/entity/ai/Brain.java
 index 328c3ecd0d35d2cad15173ec80962cee9177eaf8..625e03abc4a62f42774fedee31a5f5f776169674 100644
 --- a/src/main/java/net/minecraft/world/entity/ai/Brain.java

patches/server/0010-Make-CraftEntity-getHandle-and-overrides-perform-thr.patch

@@ -51,7 +51,7 @@ index d9687722e02dfd4088c7030abbf5008eb0a092c8..62484ebf4550b05182f693a3180bbac5
          TickThread.ensureTickThread(thisEntity, "May not tick entity scheduler asynchronously");
          final List<ScheduledTask> toRun;
 diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
-index f2d5603c6d0b3f7aa4b8f8da2c551278e4a4b091..3367fb747296ac522bede9f35007952ce54ae5c4 100644
+index 580e75595d7fc8c5af5a0281b77f7be88a25a464..5a6926e7dd5b54e7ae928ee45058663e2a13274c 100644
 --- a/src/main/java/net/minecraft/world/entity/Entity.java
 +++ b/src/main/java/net/minecraft/world/entity/Entity.java
 @@ -2767,6 +2767,7 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {