Guard triton imports in prototype.attention.quantization

[JoshBong]

Machines that do not support Triton (macOS) cannot import Triton, which breaks make html for anyone building docs locally. The import error was found in torchao.prototype.attention causing the build to fail, which I noticed while working on issue #3863.

Reproduction

make html fails with a misleading error:

      Extension error (sphinx.ext.autosummary):
      ... threw an exception (exception: no module named
  torchao.prototype.attention.fp8_fa3.attention)

The real cause, from python -c "import torchao.prototype.attention.fp8_fa3":

      File ".../fp8_fa3/__init__.py", line 11, in <module>
      File ".../fp8_fa3/attention.py", line 22, in <module>
      File ".../shared_utils/attention.py", line 28, in <module>
      File ".../quantization/__init__.py", line 7, in <module>
      File ".../quantization/triton_hadamard_qkv_quantization.py", line 25, in <module>
          import triton
      ModuleNotFoundError: No module named 'triton'

Fix

Since all of prototype.attention's triton kernel modules are imported through quantization/__init__.py, I guarded those imports with has_triton() (the same pattern as prototype/mx_formats/kernels.py). Without triton, the 5 names point to a placeholder function instead, so the package still imports and the docs build, but actually calling a kernel raises a clear error that triton is required.

Disclosure

I used Claude to help trace the import chain, but I reviewed and tested the change myself.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/ao/4967

• 📄 Preview Python docs built from this PR

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