Minetest: move_items v0

local function move_items(s_inv, s_listname, d_inv, d_listname)

    local s_list = s_inv:get_list(s_listname)
    local d_list = d_inv:get_list(d_listname)

    local s_index = 1
    local d_index = 1

    while s_index <= #s_list do
        if s_list[s_index] and not s_list[s_index]:is_empty() then
            while d_list[d_index] and (not d_list[d_index]:is_empty()) do
                d_index = d_index + 1
            end
            if d_index <= #d_list then
                d_list[d_index] = s_list[s_index]
                s_list[s_index] = nil
            else
                break
            end
        end
        s_index = s_index + 1
    end

    d_inv:set_list(d_listname, d_list)
    s_inv:set_list(s_listname, s_list)

end

minetest.register_tool(":default:asdf", {
    inventory_image = "default_wood.png",
    on_use = function(itemstack, user, pointed_thing)
        local inv = user:get_inventory()
        move_items(inv, "main", inv, "craft")
    end,
})