Fix inventory swapping not calling all callbacks (#9923)

"Predicts" whether something will be swapped for allow callbacks, then calls callbacks a second time with swapped properties. Co-authored-by: SmallJoker <SmallJoker@users.noreply.github.com>
minetest · Sep 4, 2020 · 050964b · 050964b
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diff --git a/doc/lua_api.txt b/doc/lua_api.txt
@@ -5888,6 +5888,31 @@ An `InvRef` is a reference to an inventory.
   `minetest.get_inventory(location)`.
     * returns `{type="undefined"}` in case location is not known
 
+### Callbacks
+
+Detached & nodemeta inventories provide the following callbacks for move actions:
+
+#### Before
+
+The `allow_*` callbacks return how many items can be moved.
+
+* `allow_move`/`allow_metadata_inventory_move`: Moving items in the inventory
+* `allow_take`/`allow_metadata_inventory_take`: Taking items from the inventory
+* `allow_put`/`allow_metadata_inventory_put`: Putting items to the inventory
+
+#### After
+
+The `on_*` callbacks are called after the items have been placed in the inventories.
+
+* `on_move`/`on_metadata_inventory_move`: Moving items in the inventory
+* `on_take`/`on_metadata_inventory_take`: Taking items from the inventory
+* `on_put`/`on_metadata_inventory_put`: Putting items to the inventory
+
+#### Swapping
+
+When a player tries to put an item to a place where another item is, the items are *swapped*.
+This means that all callbacks will be called twice (once for each action).
+
 `ItemStack`
 -----------
 

diff --git a/src/inventory.cpp b/src/inventory.cpp
@@ -732,26 +732,25 @@ void InventoryList::moveItemSomewhere(u32 i, InventoryList *dest, u32 count)
 u32 InventoryList::moveItem(u32 i, InventoryList *dest, u32 dest_i,
 		u32 count, bool swap_if_needed, bool *did_swap)
 {
-	if(this == dest && i == dest_i)
+	if (this == dest && i == dest_i)
 		return count;
 
 	// Take item from source list
 	ItemStack item1;
-	if(count == 0)
+	if (count == 0)
 		item1 = changeItem(i, ItemStack());
 	else
 		item1 = takeItem(i, count);
 
-	if(item1.empty())
+	if (item1.empty())
 		return 0;
 
 	// Try to add the item to destination list
 	u32 oldcount = item1.count;
 	item1 = dest->addItem(dest_i, item1);
 
 	// If something is returned, the item was not fully added
-	if(!item1.empty())
-	{
+	if (!item1.empty()) {
 		// If olditem is returned, nothing was added.
 		bool nothing_added = (item1.count == oldcount);