Codex review follow-up on PR #6880 (P2). The previous fallback
(``def is_tracing(tensor=None): return is_torchdynamo_compiling()``)
was strictly less conservative than what upstream
``transformers==4.51.3`` did inline before ``is_tracing`` was added
to ``transformers.utils.import_utils``. The pre-4.52 upstream
expression was:
is_tracing = torch.jit.is_tracing() or isinstance(
inputs_embeds, torch.fx.Proxy
) or is_torchdynamo_compiling()
The previous fallback only consulted Dynamo. That meant callers
tracing or exporting under transformers 4.51.x would silently hit
the data-dependent ``torch.all(attention_mask == 1)`` branch in
``_ignore_causal_mask_sdpa`` (and the equivalent in
``_prepare_4d_attention_mask_for_sdpa``) — failing on proxy control
flow or baking the wrong SDPA causal-mask path.
The local fallback now mirrors the legacy upstream expression:
- ``torch.jit.is_tracing()`` for ``torch.jit.trace`` /
``torch.jit.script`` flows.
- ``isinstance(tensor, torch.fx.Proxy)`` for ``symbolic_trace`` and
``torch.export`` paths that don't go through Dynamo.
- ``is_torchdynamo_compiling()`` for ``torch.compile`` and
``torch._dynamo`` paths.
The CUDA stream capture, FakeTensor, and JAX (torchax) checks the
modern ``is_tracing`` does are out of scope: those need newer
``import_utils`` helpers, and the conservative dynamo fallback is
the right choice when those helpers aren't available. This matches
the behavior of the upstream ``is_tracing`` helpers that landed in
4.52 in the first place — those were new additions, not behaviour
that pre-existed in 4.51.x.
Tests:
- ``test_import_falls_back_when_is_tracing_missing`` now exercises
all three branches (dynamo idle → False; ``torch.fx.Proxy`` arg →
True; patched ``torch.jit.is_tracing()`` → True).
- All 26 tests in ``tests/utils/test_attn_mask_compat.py`` pass.
- ``ruff check`` and ``ruff format`` clean on both files.
Signed-off-by: Taranum Wasu <taranumwasu@Taranums-MacBook-Pro.local>
Co-authored-by: Cursor <cursoragent@cursor.com>
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