Closes#65 (deferred from v0.40.3).
make_multipack_trainer_class adds a get_train_dataloader override
that builds a MultipackBatchSampler(real_batches=False) — yields a
flat list[int] per packed sequence, which is the contract HF
DataLoader.batch_sampler expects — and installs it via
DataLoader(..., batch_sampler=sampler, collate_fn=self.data_collator,
num_workers=args.dataloader_num_workers,
pin_memory=args.dataloader_pin_memory). drop_last is forwarded from
TrainingArguments.dataloader_drop_last.
Falls back to super().get_train_dataloader() when state was never
attached OR when train_dataset is unset — defence-in-depth so the
subclass remains safe to instantiate even when multipack is later
disabled.
The state-presence guard switched from falsy (`not max_seq`) to
explicit `is None` (plus `not lengths` for empty-list defence) —
attach_multipack_state already rejects non-positive ints, so the
falsy guard would only mask configurator bugs.
_get_train_sampler override stays as a defensive no-op fallback that
ALWAYS delegates to super (review-fix from v0.40.4 code-review:
returning a multipack list[list[int]] from this method would cause a
shape mismatch if any HF eval / prediction loop bypasses
get_train_dataloader and calls _get_train_sampler directly).
SFT and Pretrain trainer wrappers now invoke
make_multipack_trainer_class(SFTTrainer) and attach_multipack_state(...)
when multipack: true. The v0.40.3 yellow advisory + standard-sampler
fallback is gone. Architecture allowlist
(validate_multipack_architecture) still gates at build time.
tests/test_v0403_part_b.py: TestSftAndPretrainWiringDeferred renamed
to TestSftAndPretrainWiringLive; the deferred-state test
(_get_train_sampler returns MultipackBatchSampler when state is set)
is replaced by the live-state test (_get_train_sampler always
delegates to super even with state attached).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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