[Build Error] nvcc fatal error due to empty strings in setup.py flags (ffpa-attn)

[xachern]

Describe the bug

When building the ffpa-attn submodule in the NVIDIA PyTorch Docker container (nvcr.io/nvidia/pytorch:24.10-py3), the build fails with nvcc fatal : A single input file is required....

To Reproduce

1. Use Docker image: nvcr.io/nvidia/pytorch:24.10-py3
2. Clone the repo and submodules.
3. Run: python3 setup.py bdist_wheel && cd dist && python3 -m pip install *.whl

Error Log

nvcc fatal   : A single input file is required for a non-link phase when an outputfile is specified

The Cause

The issue is caused by empty strings '' being passed to nvcc_args in setup.py. The Ninja build system treats these empty strings as input filenames, causing nvcc to crash.

Proposed Fix

In setup.py, filter out empty strings in extra_compile_args:

# start at line 53 in setup.py

# add nvcc compile flags
"nvcc": [
    flag for flag in (
        ENV.get_build_cuda_cflags(build_pkg=True)
        + generator_flag
        + cc_flag
    )
    if flag.strip()  # <--- Filter out empty strings
],

This fix resolves the build error for me.

[DefTruth]

thanks~ Would you be willing to submit a PR to fix this issue?