Expose access to BlockEntity component.custom_data.PublicBukkitValues data

[ens-gijs]

Is your feature request related to a problem?

The PDC set on an ItemStack which results in a BlockEntity when placed (ex. shulker box) is preserved in the BlockEntity in components.custom_data.PublicBukkitValues. I would like to be able to access those values from the Block object after the ItemStack is placed. There is currently no way to do this.

Getting / setting PDC values on block.getState() instanceof TileState tileState uses PublicBukkitValues in the BlockEntity NBT for storage leaving the values in components.custom_data.PublicBukkitValues inaccessible.

Describe the solution you'd like.

I'd propose to simply change where TileState accesses and stores its PDC data. Instead of storing at the NBT root of simply PublicBukkitValues, use the BlockEntity's component storage at components.custom_data.PublicBukkitValues.

I understand this may result in unexpected or backwards incompatible behavior, it may prove difficult to deal with existing blocks that have both the old and new storage locations, and a multitude of other challenges may exist. In which case please consider adding an additional method on TileState to retrieve the BlockEntites component stored PDC data, something like PersistentDataContainer getBlockEntityPersistentDataContainer(); (or choose a better semantic name ;).

Describe alternatives you've considered.

Dealing with the hell of trying to capture ItemStack PDC into TileState PDC then restore TileState PDC values during the item->block->item lifecycle.

Other

No response

[NonSwag]

I'd suggest adding a data fixer to move all BukkitDataValues to custom data
and make PDC only access custom_data

[electronicboy]

The PDC serves as a means of allowing you to store data onto something itself, the component stored in the block entity doesn't directly belong to the block entity, it belongs to the block that placed it down; dealing with moving data around would induce work for us to do which introduces a level of data corruption and passaround otherwise unexpected, so, I generally just cannot support such a move and feel that it would be a dangerous change in general.

Exposing the stored stack component is something that I've had some considerations towards

[ens-gijs]

With loot table modification (via data pack) the BlockEntity component_data can be configured to survive the block->item lifecycle as well. For my specific usecase at hand, having readonly access to the BlockEntity component_data stored PDC would suffice. However, I can easily foresee situations where I may want to modify that state so when the block transitions back to an item everything would be consistent. I'm onboard with keeping TileState PDC and the BlockEntity component_data stored PDC separate if paper eng feels it more appropriate.

My current hack-around for not having access to the BlockEntity component_data stored PDC, captured from the ItemStack that created the block, is to simply copy the ItemStack's PDC into the Block's PDC when the block is placed. This, effectively gives me the read-only view I require... but it doesn't work when a BlockEntity placed via a Dispenser - in which case the ItemStack and created block don't seem to be exposed within a single event. So for now I'm canceling the BlockDispenseEvent event - which is fine for my current use case but again is limiting.

I do not have an effective solution to copy the PDC back out of the block and into a dropped item, the challenge is around the multitude of events that may be fired when a block is broken and their inconsistency in providing the source block and the dropped Item or ItemStack. Explosions events for example provide the list of blocks, but not items/stacks.

    // Handler to copy PDC data for the item->block life cycle stage
    // Note the block->item life cycle state is handled by the custom datapack which this plugin injects (loot tables).
    @EventHandler(priority = EventPriority.HIGHEST, ignoreCancelled = true)
    public void onEvent(BlockPlaceEvent event) {
        ItemStack stack = event.getItemInHand();
        if (stack != null && !stack.isEmpty()) {
            var pdcv = stack.getPersistentDataContainer();
            if (!pdcv.isEmpty()) {
                Block block = event.getBlockPlaced();
                try {
                    TileState tileState = (TileState) block.getState(false);
                    pdcv.copyTo(tileState.getPersistentDataContainer(), false);
                } catch (Exception ex) {
                    logger.log(Level.SEVERE, "BlockPlaceEvent Failed to transfer PDC state during item->block lifecycle", ex);
                }
            }
        }
    }