[MUSA] Update 3rd party dir to build/_deps

[yeahdongcn]

Motivation

The MUSA build previously cloned third-party repositories (mutlass, flashinfer) into sgl-kernel/third_party/, which polluted the source tree and required explicit .gitignore entries. This was inconsistent with the CUDA CMake build, which uses FetchContent to clone dependencies into build/_deps/ - a directory already ignored by the existing **/build/ pattern in .gitignore.

Modifications

• sgl-kernel/setup_musa.py:

  • Change default third-party directory from third_party to build/_deps to match CMake's FetchContent behavior
  • Add SGLANG_MUSA_THIRD_PARTY_DIR environment variable for custom override
  • Rename SKIP_THIRD_PARTY to SGLANG_MUSA_SKIP_THIRD_PARTY for consistent naming convention
  • Add parents=True to mkdir() to create full directory hierarchy

• .gitignore:

  • Remove sgl-kernel/third_party/ entries (no longer needed since build/_deps/ is covered by **/build/)

Testing Done

sgl-kernel build on MUSA passed.

Accuracy Tests

Benchmarking and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.
• Follow the SGLang code style guidance.

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[gemini-code-assist]

Summary of Changes

Hello @yeahdongcn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the MUSA build process to standardize how third-party dependencies are managed. By relocating these dependencies from a source-tree-polluting sgl-kernel/third_party/ to the build/_deps/ directory, it achieves consistency with the CUDA CMake build and leverages existing .gitignore rules. This change streamlines the build environment, reduces clutter, and improves maintainability.

Highlights

• Third-party directory relocation: The default directory for third-party dependencies has been changed from sgl-kernel/third_party/ to build/_deps/ in sgl-kernel/setup_musa.py. This aligns with the CUDA CMake build's dependency handling.
• Environment variable for custom directory: A new environment variable, SGLANG_MUSA_THIRD_PARTY_DIR, has been introduced in sgl-kernel/setup_musa.py to allow users to specify a custom location for third-party dependencies.
• Consistent environment variable naming: The environment variable SKIP_THIRD_PARTY has been renamed to SGLANG_MUSA_SKIP_THIRD_PARTY in sgl-kernel/setup_musa.py for better naming consistency.
• Directory creation robustness: The mkdir() call in sgl-kernel/setup_musa.py now includes parents=True, ensuring that all necessary parent directories are created if they don't already exist.
• .gitignore cleanup: Specific .gitignore entries for sgl-kernel/third_party/ have been removed, as the new build/_deps/ location is already covered by existing **/build/ rules.

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[gemini-code-assist]

Code Review

This pull request refactors the MUSA build process to handle third-party dependencies more cleanly, moving them from the source tree to a build/_deps directory. This aligns with the CUDA build process and simplifies the .gitignore file. The changes are well-motivated and improve consistency. However, I've found a critical issue in path construction for the new third-party directory that will likely cause the build to fail. I've provided a suggestion to fix this.