Revert "Build PyTorch wheel via PEP 517 instead of setup.py" (#21562)

[shoumikhin]

Reverts the install_pytorch.sh change from #21562.

Why

#21562 broke test-riscv on main. 17 of 17 jobs, on every commit that has landed since it went in. Failing step is pip install --no-build-isolation extension/llm/tokenizers:

[299/312] Generating CXX dyndep file CMakeFiles/pytorch_tokenizers_cpp.dir/CXX.dd
FAILED: CMakeFiles/pytorch_tokenizers_cpp.dir/src/python_bindings.cpp.o
cc1plus: error: to generate dependencies you must specify either '-M' or '-MM'

Cause

The PEP 517 change itself is correct and should come back. The problem is how the build requirements are installed.

To run python -m build --wheel --no-isolation, #21562 installs build, scikit-build-core, setuptools, cmake and ninja permanently into the image's conda environment. scikit-build-core ships a setuptools plugin that registers itself as the build_ext command class. Every later pip install --no-build-isolation in that image then runs its CMake configure instead of the plain setuptools one, which switches on C++20 module dependency scanning. The image's GCC 14.2.0 cannot produce the scan output CMake asks for, so the tokenizers build dies.

Two greps confirm it. dyndep has zero hits in the last green job log and one in the red one. scikit_build_core is absent from the green log and present in the red traceback.

Why CI did not catch it

test-riscv lives in its own workflow, Test RISC-V Backend. It does not run on pull requests unless the change touches specific RISC-V paths, it is not a required merge context, and it does not gate viable/strict. So nothing in the pre-merge gate could have seen this.

Next

Re-landing separately with the build requirements confined to a throwaway virtualenv, so they stop leaking into every later build in the image. That PR will carry a ciflow/trunk tag so test-riscv actually runs on it before it merges.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21684

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure

As of commit a02e38d with merge base a439afd ():

NEW FAILURE - The following job has failed:

• pull / unittest-editable / linux / linux-job (gh)
  ##[error]fatal: unable to access 'https://github.com/zeux/volk/': Error in the HTTP2 framing layer

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