Fix is_last off-by-one in MaskGenerationPipeline for partial batches

[J3r3myPerera]

Fixes #46123

MaskGenerationPipeline.preprocess used i == n_points - points_per_batch to spot the last batch. When n_points isn't a multiple of points_per_batch, that's never true — PipelinePackIterator hits StopIteration and quietly drops the last batch's results.

Fix: i + points_per_batch >= n_points.
Two fast unit tests in test_pipelines_mask_generation.py: one for the partial-batch case (100 points, batch 64), one for an exact multiple (128 points, batch 64).

python -m pytest tests/pipelines/test_pipelines_mask_generation.py::MaskGenerationPipelineTests::test_preprocess_is_last_partial_batch tests/pipelines/test_pipelines_mask_generation.py::MaskGenerationPipelineTests::test_preprocess_is_last_exact_multiple -v
#2 passed

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  Discussed in MaskGenerationPipeline: is_last never True on final partial batch, silently dropping results #46123
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• Did you write any new necessary tests?
  Added test_preprocess_is_last_partial_batch and test_preprocess_is_last_exact_multiple to tests/pipelines/test_pipelines_mask_generation.py.

Who can review?

cc @Rocketknight1 @yonigozlan @qubvel

[Shashank-Tripathi-07]

Hey bro, the code looks good but you said you didn't use AI agents to make this PR but there are em dashes very visible on the comment you made and also in the original issue. This can be a problem as the repo doesn't like Agent Slop even 1%. Take a look again for safety on this.

[J3r3myPerera]

The CI failures here are pre-existing on main — not caused by this change.
ci/circleci: tests_tensor_parallel_ci — all 3 failures are in Cohere2MoeModelTest (test_tp_forward, test_tp_backward, test_tp_generation), crashing with KeyError: 'rowwise' in distributed/tensor_parallel.py. This PR doesn't touch any of that.

ci/circleci: tests_training_overfit_ci — 1 failure, also Cohere2MoeModelTest::test_training_overfit, loss only drops 27% vs a 90% threshold. Unrelated.

Only two files changed:

src/transformers/pipelines/mask_generation.py (1 line)
tests/pipelines/test_pipelines_mask_generation.py (2 tests)

Neither touches Cohere2MoeModel or anything in the distributed training path.

[J3r3myPerera]

Hey bro, the code looks good but you said you didn't use AI agents to make this PR but there are em dashes very visible on the comment you made and also in the original issue. This can be a problem as the repo doesn't like Agent Slop even 1%. Take a look again for safety on this.

Fair point, and I'll own it. I did use AI to help word the PR description and the issue comment. The fix itself I worked out on my own: i == n_points - points_per_batch only hits when n_points is an exact multiple, so any partial tail batch never gets flagged as last, PipelinePackIterator raises StopIteration and the results are quietly dropped. Replacing it with i + points_per_batch >= n_points handles both cases. I understand what the code does and why the old condition was wrong.

That said, em dashes in prose aren't really a reliable signal for agent-generated code. Plenty of people type them on purpose. The actual thing to check is whether the logic holds up. Which I'd rather be judged on.

[Rocketknight1]

You can ignore those comments, he's just annoyed I wouldn't listen when he claimed his Claude PR was human-written. In this case the actual fix is one line and seems correct, so I don't really care too much whether an agent wrote it or not. You do not actually need to go around hiding all the em-dashes 😅

[Rocketknight1]

Looks good! I did a little cleanup to shorten the tests a lot - a regression test for the behaviour is nice, but we want to avoid 60 LOC of tests for a one-line fix, it's a bit agent-sloppy. The fix was good, though!

[Rocketknight1]

@J3r3myPerera looks like there might be some CI instability at the moment. Can you wait a bit and then try rebasing or rerunning tests? Once the CI is green ping me and I'll merge it.

[github-actions]

View the CircleCI Test Summary for this PR:

https://huggingface.co/spaces/transformers-community/circle-ci-viz?pr=46136&sha=ba5335

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