InvRef: Add convenience method add_list for bulk transfer of items

[ClobberXD]

• New Lua API method InvRef:add_list(dst_listname, src_listname) for bulk transfer of items from one inventory list to another.
• Returns the leftover items as an inventory list.
• New internal function push_inventory_list_raw (declared/defined in c_content.{h|cpp}) to directly push an InventoryList * object to the Lua stack. Existing function push_inventory_list now makes use of push_inventory_list_raw internally.

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To test:

• Install and enable luacmd mod.
• Populate at least 10 slots with unique items in the main inventory list.
• Type the following into the console:

  /lua inv = me:get_inventory()
  /lua inv:set_list("main", inv:add_list("craft", "main"))

The above chat-command transfers all items in main to the crafting grid and sets the leftover back to main. Since there were more than 9 unique items in main, there's bound to be at least one item as leftover.

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Closes #7663. Tested, works as expected.

[Desour]

I think, this would be more useful if it worked between different inventories, too.

[ClobberXD]

Fixed src list being destroyed after the bulk transfer. Apparently, I was trying to push a non-existent list to the Lua stack, because I was using push_inventory_list in spite of using an independent InventoryList * object. See the updated first post for more details.

I think, this would be more useful if it worked between different inventories, too.

I agree. I'll see what I can do.

[SmallJoker]

Why do you need it as pointer?
InventoryList leftover_list("leftover", src_list->getSize(), getServer(L)->getItemDefManager());
EDIT: and push_inventory_list_raw(L, &leftover_list);

[SmallJoker]

getList may return nullptr is that list does not exist. Check for that.

[ClobberXD]

Will do.

[SmallJoker]

The above chat-command transfers all items in main to the crafting grid

So they're moved? The code does indicate that the list is copied,.
Here's how transferring item lists would work entirely in Lua:

local src = inv:get_list("main")
for i = 1, #src do
	src[i] = dst:add_item("craft", src[i])
end
inv:set_list("main", src)

[ClobberXD]

@SmallJoker Correct - they're moved. After all, this is a convenience method to achieve exactly what the Lua code you posted does - bulk transfer of items from one list to another.

The name might cause some confusion, though. add_list sounds like a method that creates a new inv. list. Should I rename it to something like move_list?

[SmallJoker]

@ClobberXD move_list would indeed fit better. Although I really doubt this function is generic enough to be helpful for most mods. It makes the list item transfer easier, but a five lines of Lua code can do the same - which is a very little amount of code.
I'm not entirely against this PR, but would like to hand over reviewing & approving to the other devs.

[ClobberXD]

I too am starting to doubt the necessity of this convenience function, given the implementation effort. But that got me thinking, would it make sense to implement this in Lua and add it to builtin?

[ClobberXD]

Closing due to lack of solid use-cases and lack of core dev interest.