name: 'Download prebuilt Rust extensions'
description: >
  Put rust-ext-build's PyO3 extension modules in the checkout and set
  SGLANG_BUILD_RUST_EXTS=none and SGLANG_RUST_BUILD_MODE=never for the job, so
  install skips the cargo build and runtime trusts these fingerprinted modules.
  Sets nothing when neither source has them, leaving source builds enabled.

inputs:
  artifact_name:
    description: "rust-ext-build's artifact in this run; empty uses only the cache."
    required: false
    default: ''
  cache_key_prefix:
    description: 'Must match what _pr-test-rust-ext-build.yml saves under.'
    required: false
    default: rust-ext-x86_64-cp310-cp312

outputs:
  hit:
    description: "'true' when the modules are in place, for callers that install a Rust toolchain only to build them."
    value: ${{ steps.decide.outputs.hit }}

runs:
  using: composite
  steps:
    # continue-on-error: the artifact expires in a day, so a re-run falls through
    # to the cache below.
    - name: Download prebuilt Rust extensions
      id: artifact
      if: inputs.artifact_name != ''
      continue-on-error: true
      uses: actions/download-artifact@v4
      with:
        name: ${{ inputs.artifact_name }}
        path: python/sglang/srt/

    # Gated with the restore below, not run unconditionally: a job whose artifact
    # arrived never reads the cache, so it should not pay an apt-get for it. The
    # self-hosted images ship without zstd, and the entries were saved with it.
    - name: Ensure zstd so the cache entry is readable
      if: steps.artifact.outcome != 'success'
      shell: bash
      run: bash scripts/ci/utils/ensure_zstd.sh

    # Second, not first: the cache is evictable and this repo sits at its 10 GB
    # limit. A run reads its own branch's entries plus the default branch's, so
    # seed-rust-ext-cache.yml and the branch's own rust-ext-build both land here.
    - name: Restore prebuilt Rust extensions from cache
      id: cache
      if: steps.artifact.outcome != 'success'
      uses: actions/cache/restore@v4
      with:
        path: |
          python/sglang/srt/rust_extensions/_*.so
          python/sglang/srt/mem_cache/rust_tree_core/mem_cache*.so
        key: ${{ inputs.cache_key_prefix }}-${{ hashFiles('rust/**', 'proto/**', 'python/setup.py', 'python/pyproject.toml', 'python/sglang/srt/rust_extensions/torch_build.py', '.github/workflows/_pr-test-rust-ext-build.yml', 'scripts/ci/utils/stage_rust_ext_modules.sh') }}

    # Job-wide, but only setup.py reads it, and only while building.
    # Whether the modules suit this interpreter is not decided here:
    # require_prebuilt_rust_exts checks them against the local EXT_SUFFIX and
    # clears this back to a source build on a mismatch.
    - name: Decide whether to skip the cargo build
      id: decide
      shell: bash
      run: |
        set -uo pipefail
        if [ "${{ steps.artifact.outcome }}" = "success" ] \
           || [ "${{ steps.cache.outputs.cache-hit }}" = "true" ]; then
            echo "hit=true" >> "$GITHUB_OUTPUT"
            echo "SGLANG_BUILD_RUST_EXTS=none" >> "$GITHUB_ENV"
            # A source checkout normally ignores in-package native artifacts
            # because they may be stale. These are fingerprint-keyed CI bytes.
            echo "SGLANG_RUST_BUILD_MODE=never" >> "$GITHUB_ENV"
        else
            echo "hit=false" >> "$GITHUB_OUTPUT"
        fi