[#SPIGOT-4576] ItemStacks serialized with attributes in 1.12.2 cannot be deserialized correctly in 1.13.2

Particularly, attribute modifiers are lost.

Give yourself an item with attributes:

/give @p diamond_sword 1 0 {AttributeModifiers:[{AttributeName:"generic.attackDamage",Name:"generic.attackDamage",Amount:1000,Operation:0,UUIDMost:64497,UUIDLeast:746848}]}

Serialize it using git-Spigot-e8ded36-acbc348 (MC: 1.12.2):

Player p = ...;
ItemStack it = p.getItemInHand();
YamlConfiguration cfg = new YamlConfiguration();
cfg.set("item", it);
cfg.save(new File(getDataFolder(), "item.yml"));

The generated YAML looks like this:

item:   ==: org.bukkit.inventory.ItemStack
  type: DIAMOND_SWORD
  meta:     ==: ItemMeta
    meta-type: UNSPECIFIC
    internal: H4sIAAAAAAAAAHWNMQ6CQBBFv1ljFggN8RzegYSGRLCiZ8SRTMzummW4s601jWtjZ/nyft7PgQxVrRrluip34SZ34bjkAHYGdhjapguLAtvbIPvimSlxwaPBoXZh9Umal0X5q/TkGMeZPUeZTqRK06MhRzOnxOXJkVSCTw+w2P8fAx9NnKb/ngAAAA==

Then load it using git-Spigot-f56e2e7-07e504c (MC: 1.13.2)

Player p = (Player) sender;
YamlConfiguration cfg = YamlConfiguration.loadConfiguration(new File(getDataFolder(), "item.yml"));
p.getLocation().getWorld().dropItem(p.getLocation(), cfg.getItemStack("item"));

The deserialized item has its attributes missing.

I've written a workaround trying to convert the Itemstack yaml: https://github.com/RecursiveG/YamlUpgrader which generates yaml that can be loaded by 1.13.2:

item:   ==: org.bukkit.inventory.ItemStack
  v: 1631
  type: DIAMOND_SWORD
  meta:     ==: ItemMeta
    meta-type: UNSPECIFIC
    attribute-modifiers:       GENERIC_ATTACK_DAMAGE:       - ==: org.bukkit.attribute.AttributeModifier
        amount: 1000.0
        name: generic.attackDamage
        uuid: 00000000-0000-fbf1-0000-0000000b6560
        operation: 0

[SPIGOT-4576] ItemStacks serialized with attributes in 1.12.2 cannot be deserialized correctly in 1.13.2 Created: 13/Jan/19 Updated: 13/Jan/19 Resolved: 13/Jan/19
Status:	Resolved
Project:	Spigot
Component/s:	None
Affects Version/s:	None
Fix Version/s:	None

[SPIGOT-4576] ItemStacks serialized with attributes in 1.12.2 cannot be deserialized correctly in 1.13.2 Created: 13/Jan/19 Updated: 13/Jan/19 Resolved: 13/Jan/19