[Build] Skip spinloop extension on Python < 3.11

[Jasen2201]

The spinloop extension uses Py_buffer, PyBuffer_Release, and the "y*" format code in PyArg_ParseTupleAndKeywords — none of which are available in the Python Limited/Stable API. Combined with USE_SABI 3.11, this causes compilation to fail on Python 3.10 because the Limited API headers do not declare these symbols.

Guard the spinloop target in both CMakeLists.txt (Python_VERSION check) and setup.py (sys.version_info check) so the build skips it on older interpreters. This aligns build-time behavior with the existing runtime fallback (try/except import in vllm/_spinloop.py) and keeps vLLM buildable on Python 3.10, which is still within the declared requires-python range (>=3.10,<3.15).

Purpose

Test Plan

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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[claude]

Claude Code Review

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[Jasen2201]

This issue was introduced by #36517

[Harry-Chen]

I think it is fixed by #43659?

[Jasen2201]

I think it is fixed by #43659?

Not exactly. #43659 only fixed the runtime side (added try/except ImportError in Python). The build itself still fails on Python 3.10 because spinloop.cpp uses Py_buffer which is unavailable under Py_LIMITED_API. You never get a wheel, so the runtime fallback never gets a chance to run. This PR adds the missing build-time guard.

[Harry-Chen]

@Jasen2201 Please add sign-off to your commits

[Jasen2201]

@Jasen2201 Please add sign-off to your commits

Done, rebased onto the latest origin/main and added Signed-off-by.

[Jasen2201]

The CI failure is unrelated to this PR @Harry-Chen

[mergify]

Hi @zhyajie, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

[Jasen2201]

Hi @zhyajie, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

https://github.com/vllm-project/vllm/actions/runs/27285824805/job/80592869532?pr=44783 The update-dockerfile-graph hook failure is unrelated to this PR. It's caused by a pre-existing mismatch between docker/Dockerfile and docs/assets/contributing/dockerfile-stages-dependency.png on main. This PR only modifies CMakeLists.txt — no Dockerfile changes involved.

[pschlan-amd]

Thanks for fixing this!