Fix vanilla inventory wrappers not properly calling markDirty. Closes #3854 and #3810

Also updated IItemHandler javadocs to reflect returning EMPTY instead of NULL.

src/main/java/net/minecraftforge/items/IItemHandler.java

@@ -62,7 +62,7 @@ public interface IItemHandler
      * @param slot     Slot to insert into.
      * @param stack    ItemStack to insert.
      * @param simulate If true, the insertion is only simulated
-     * @return The remaining ItemStack that was not inserted (if the entire stack is accepted, then return null).
+     * @return The remaining ItemStack that was not inserted (if the entire stack is accepted, then return ItemStack.EMPTY).
      *         May be the same as the input ItemStack if unchanged, otherwise a new ItemStack.
      **/
     @Nonnull
@@ -76,7 +76,7 @@ public interface IItemHandler
      * @param slot     Slot to extract from.
      * @param amount   Amount to extract (may be greater than the current stacks max limit)
      * @param simulate If true, the extraction is only simulated
-     * @return ItemStack extracted from the slot, must be null, if nothing can be extracted
+     * @return ItemStack extracted from the slot, must be ItemStack.EMPTY, if nothing can be extracted
      **/
     @Nonnull
     ItemStack extractItem(int slot, int amount, boolean simulate);

src/main/java/net/minecraftforge/items/VanillaDoubleChestItemHandler.java

@@ -131,6 +131,10 @@ public class VanillaDoubleChestItemHandler extends WeakReference<TileEntityChest
                 ((IItemHandlerModifiable) singleHandler).setStackInSlot(targetSlot, stack);
             }
         }
+
+        chest = getChest(!accessingUpperChest);
+        if (chest != null)
+            chest.markDirty();
     }
 
     @Override
@@ -140,7 +144,19 @@ public class VanillaDoubleChestItemHandler extends WeakReference<TileEntityChest
         boolean accessingUpperChest = slot < 27;
         int targetSlot = accessingUpperChest ? slot : slot - 27;
         TileEntityChest chest = getChest(accessingUpperChest);
-        return chest != null ? chest.getSingleChestHandler().insertItem(targetSlot, stack, simulate) : stack;
+        if (chest == null)
+            return stack;
+
+        int starting = stack.getCount();
+        ItemStack ret = chest.getSingleChestHandler().insertItem(targetSlot, stack, simulate);
+        if (ret.getCount() != starting && !simulate)
+        {
+            chest = getChest(!accessingUpperChest);
+            if (chest != null)
+                chest.markDirty();
+        }
+
+        return ret;
     }
 
     @Override
@@ -150,7 +166,18 @@ public class VanillaDoubleChestItemHandler extends WeakReference<TileEntityChest
         boolean accessingUpperChest = slot < 27;
         int targetSlot = accessingUpperChest ? slot : slot - 27;
         TileEntityChest chest = getChest(accessingUpperChest);
-        return chest != null ? chest.getSingleChestHandler().extractItem(targetSlot, amount, simulate) : ItemStack.EMPTY;
+        if (chest == null)
+            return ItemStack.EMPTY;
+
+        ItemStack ret = chest.getSingleChestHandler().extractItem(targetSlot, amount, simulate);
+        if (!ret.isEmpty() && !simulate)
+        {
+            chest = getChest(!accessingUpperChest);
+            if (chest != null)
+                chest.markDirty();
+        }
+
+        return ret;
     }
 
     @Override

src/main/java/net/minecraftforge/items/wrapper/SidedInvWrapper.java

@@ -112,7 +112,7 @@ public class SidedInvWrapper implements IItemHandlerModifiable
                 {
                     ItemStack copy = stack.copy();
                     copy.grow(stackInSlot.getCount());
-                    inv.setInventorySlotContents(slot1, copy);
+                    setInventorySlotContents(slot1, copy);
                 }
 
                 return ItemStack.EMPTY;
@@ -125,7 +125,7 @@ public class SidedInvWrapper implements IItemHandlerModifiable
                 {
                     ItemStack copy = stack.splitStack(m);
                     copy.grow(stackInSlot.getCount());
-                    inv.setInventorySlotContents(slot1, copy);
+                    setInventorySlotContents(slot1, copy);
                     return stack;
                 }
                 else
@@ -147,7 +147,7 @@ public class SidedInvWrapper implements IItemHandlerModifiable
                 stack = stack.copy();
                 if (!simulate)
                 {
-                    inv.setInventorySlotContents(slot1, stack.splitStack(m));
+                    setInventorySlotContents(slot1, stack.splitStack(m));
                     return stack;
                 }
                 else
@@ -159,7 +159,7 @@ public class SidedInvWrapper implements IItemHandlerModifiable
             else
             {
                 if (!simulate)
-                    inv.setInventorySlotContents(slot1, stack);
+                    setInventorySlotContents(slot1, stack);
                 return ItemStack.EMPTY;
             }
         }
@@ -172,7 +172,12 @@ public class SidedInvWrapper implements IItemHandlerModifiable
         int slot1 = getSlot(inv, slot, side);
 
         if (slot1 != -1)
-            inv.setInventorySlotContents(slot1, stack);
+            setInventorySlotContents(slot1, stack);
+    }
+
+    private void setInventorySlotContents(int slot, ItemStack stack) {
+      inv.markDirty(); //Notify vanilla of updates, We change the handler to be responsible for this instead of the caller. So mimic vanilla behavior
+      inv.setInventorySlotContents(slot, stack);
     }
 
     @Override
@@ -211,7 +216,9 @@ public class SidedInvWrapper implements IItemHandlerModifiable
         else
         {
             int m = Math.min(stackInSlot.getCount(), amount);
-            return inv.decrStackSize(slot1, m);
+            ItemStack ret = inv.decrStackSize(slot1, m);
+            inv.markDirty();
+            return ret;
         }
     }