Add vLLM-metax vllm metax cmake presets output flag

[ghangz]

Summary

• Adds a focused vllm metax cmake presets output flag improvement for MetaX-MACA/vLLM-metax.
• The change targets MetaX MACA development and validation workflows, with emphasis on earlier diagnostics, reproducible logs, or safer benchmark tooling.
• Existing default behavior is kept compatible; the new logic is scoped to explicit checks, helper tools, or validation metadata.

Validation

• Verified on Gitee.AI MetaX GPU resources: vLLM-metax_vLLM image batch, 10/10 PASS; PyTorch-MACA batch also covered vLLM-metax runtime tools.
• Branch validation command: python -m pytest tests/tools/test_generate_cmake_presets_output.py
• Pull request text is intentionally ASCII-only to avoid encoding issues on web forms and API clients.

Review notes

• Source branch: ghangz:mengz/vllm-metax-cmake-presets-output-flag
• Target branch: MetaX-MACA/vLLM-metax:master
• Maintainers can modify this branch if follow-up adjustments are needed.

[gemini-code-assist]

Code Review

This pull request adds an --output command-line argument to generate_cmake_presets.py to allow specifying a custom output path, and includes a test to verify this behavior. The review feedback points out a dangerous global mock of os.path.exists in the new test and suggests a safer alternative of creating a dummy file in the temporary directory.

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[gemini-code-assist]

Mocking os.path.exists globally via monkeypatch.setattr(presets.os.path, "exists", ...) is highly discouraged and dangerous. Since os.path is a shared module, this mock affects the entire Python process during the test execution, which can cause unpredictable failures or hangs in other tests, pytest internals, or teardown processes.\n\nInstead of mocking os.path.exists, you can simply create the dummy nvcc file in the temporary directory tmp_path. This allows the real os.path.exists to return True naturally and safely.

    nvcc_bin = tmp_path / "bin"\n    nvcc_bin.mkdir(parents=True, exist_ok=True)\n    (nvcc_bin / "nvcc").touch()\n\n    monkeypatch.setattr(presets, "CUDA_HOME", str(tmp_path))\n    monkeypatch.setattr(presets, "which", lambda name: None)\n    monkeypatch.setattr(presets, "get_cpu_cores", lambda: 8)