sgl-project/sglang · error · RuntimeError

Rust sources under {crate.workspace} changed during the buil

Error message

Rust sources under {crate.workspace} changed during the build; the result was not cached

What it means

Raised by load_rust_extension after a Cargo build completes when the digest of the Rust workspace sources changed while cargo was running, meaning the produced artifact may not match the sources. The loader refuses to cache a possibly stale artifact.

Source

Thrown at python/sglang/srt/rust_extensions/loader.py:126

    lock_path = (
        cache_root / "locks" / f"{crate.package}-{context.target_fingerprint}.lock"
    )

    with _filesystem_lock(lock_path):
        if mode != "force" and extension_path.is_file():
            return _load_extension_from_path(crate.python_module, extension_path)

        if mode == "never":
            raise ModuleNotFoundError(
                f"{crate.python_module} is not bundled or cached, and Rust extension "
                "build mode is 'never'",
                name=crate.python_module,
            )

        target_dir = cache_root / "targets" / context.target_fingerprint
        artifact = _cargo_build(crate, target_dir)
        if _source_digest(crate.workspace) != context.source_digest:
            raise RuntimeError(
                f"Rust sources under {crate.workspace} changed during the build; "
                "the result was not cached"
            )
        _stage_atomically(artifact, extension_path)
        return _load_extension_from_path(crate.python_module, extension_path)


def _import_bundled_extension(module_name: str) -> ModuleType | None:
    try:
        return importlib.import_module(module_name)
    except ModuleNotFoundError as exc:
        if exc.name == module_name:
            return None
        raise


def _discover_crate(workspace: Path, python_module: str) -> _CrateSpec:
    workspace = Path(workspace).resolve()

View on GitHub (pinned to 0132848349)

Solutions

1. Ensure no process modifies the Rust workspace during the build (stop formatters, codegen, git operations)
2. Retry the load after the concurrent modification finishes
3. If persistent, verify no watcher (e.g. cargo watch, dev server) rewrites sources; clean and rebuild

try:
    mod = load_rust_extension(module, workspace)
except RuntimeError as e:
    if "changed during the build" in str(e):
        mod = load_rust_extension(module, workspace)  # retry once after edits settle
    else:
        raise

When it happens

Trigger: Calling load_rust_extension while Rust sources under the crate workspace are being modified (editor auto-format, codegen, git checkout) concurrently with the build.

Common situations: Building the Rust extension in a repo that is being actively edited, or a build tool/IDE touches Cargo.toml/sources mid-build; git operations running in parallel.

Related errors

• Rust workspace for {python_module} was not found at {workspa
• {lockfile} is required for reproducible `cargo build --locke
• {manifest} declares python-module {python_module!r} but must
• failed to build {crate.python_module} with Cargo
• Cargo completed but did not produce the expected artifact {a

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/5af5e3985a9c84bf. Report an issue: GitHub.