Fast NBT

1.20-26.9.1-forge

Fixed

• NBT data loss in CompoundTag.merge. The merge of a nested compound mutated the target and then replaced it with a copy of the incoming tag, so every key that existed only in the target disappeared. This affects anything that merges NBT: /data merge, the loot table NBT functions (set_nbt, set_contents), placing a block with a BlockEntityTag, spawn eggs carrying an EntityTag, and every mod that merges into its own NBT or saved data. This is the only data-loss fix since 1.2 — see issue #4.

Added

• Configuration. config/fastnbt.toml is generated on first launch and gives every optimization its own switch, plus a global enabled. Injection is decided by the mixin config plugin, so turning a feature off puts the vanilla method back instead of just skipping it at runtime.
• blockStateCodec — chunk section palettes resolve the canonical {Name, Properties} tag directly instead of walking the full DFU codec chain (dispatch codec, registry lookup, one MapCodec per property, plus DataResult / Either / Pair / Optional allocations) on every chunk load and save. Decoding only: encoding is untouched, so saved chunks and network packets stay byte-identical.
• nbtIo — unlimited NBT readers skip a byte-accounting pass whose result is discarded. That covers every chunk load, plus level.dat and playerdata.
• itemStack and blockState — the existing ItemStack and block-state NBT paths are now switchable features instead of always-on.

Changed

• The ItemStack#isEnchanted replacement was removed; vanilla's implementation is used again.
• The CompoundTag rewrites have no separate switch — the global enabled flag controls them.
• All mixins now carry priority = 100000.

Notes

• Only canonical data takes a fast path. Non-canonical data is reported as a decode error rather than guessed at, with one deliberate exception to vanilla: an unknown block id is an error here where vanilla resolved it to air, so chunk palette decoding promotes it to air itself and logs one line per entry.
• Full description, configuration and compatibility notes: README.