sgl-project/sglang · error · ModuleNotFoundError

no Cargo package under {workspace} declares `[package.metada

Error message

no Cargo package under {workspace} declares `[package.metadata.sglang] python-module = "{python_module}"`; declared modules: {sorted(declared_modules)}

What it means

No Cargo package in the workspace declares the requested Python module via `[package.metadata.sglang] python-module = "..."`. The message lists the modules that ARE declared to aid diagnosis.

Source

Thrown at python/sglang/srt/rust_extensions/loader.py:192

        package_name = package.get("name")
        library = document.get("lib", {}).get("name")
        if not package_name or not library:
            raise ValueError(
                f"{manifest} declares python-module {python_module!r} but must "
                "also set `package.name` and `lib.name`"
            )
        matches.append(
            _CrateSpec(
                package=package_name,
                library=library,
                python_module=python_module,
                workspace=workspace,
                features=tuple(sglang_metadata.get("features", ())),
            )
        )

    if not matches:
        raise ModuleNotFoundError(
            f"no Cargo package under {workspace} declares "
            f'`[package.metadata.sglang] python-module = "{python_module}"`; '
            f"declared modules: {sorted(declared_modules)}",
            name=python_module,
        )
    if len(matches) > 1:
        raise ValueError(
            f"multiple Cargo packages under {workspace} declare python module "
            f"{python_module!r}: {sorted(crate.package for crate in matches)}"
        )
    return matches[0]


def _build_context(crate: _CrateSpec) -> _BuildContext:
    source_digest = _source_digest(crate.workspace)
    toolchain = {
        "cargo": _command_version(
            "cargo", "--version", "--verbose", cwd=crate.workspace

View on GitHub (pinned to 0132848349)

Solutions

1. Check the declared modules list in the message and fix the python_module spelling
2. Add a `[package.metadata.sglang] python-module = "..."` entry to the intended crate's Cargo.toml
3. Ensure the crate lives under the workspace being scanned

import tomllib, pathlib
declared = set()
for p in pathlib.Path(ws).rglob("Cargo.toml"):
    d = tomllib.loads(p.read_text())
    m = d.get("package",{}).get("metadata",{}).get("sglang",{}).get("python-module")
    if m: declared.add(m)
assert python_module in declared

When it happens

Trigger: Calling load_rust_extension with a python_module string that no crate's sglang metadata declares (typo, module not yet registered).

Common situations: Renaming a Python module without updating Cargo metadata; adding a new extension without the metadata block; misspelling the dotted module name.

Related errors

• multiple Cargo packages under {workspace} declare python mod
• Rust workspace for {python_module} was not found at {workspa
• {name} must have dtype torch.int32
• {name} must be on the same device as block sparse tensors
• {name} must live on CUDA

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/2ca42d2671fd21c5. Report an issue: GitHub.