rust-lang/cargo · error

parsing ` ` requires `-Zscript

Error message

parsing `{}` requires `-Zscript`

What it means

Thrown by read_toml_string when the manifest file is detected as an embedded (single-file script) manifest — identified by frontmatter or shebang — but the -Zscript unstable feature is not enabled in the global context. Embedded manifests are an unstable cargo feature; without the gate, cargo refuses to expand the script's frontmatter into a real manifest.

Solutions

1. Enable the unstable feature: add -Zscript to the cargo invocation (requires nightly cargo).
2. If you did not intend an embedded manifest, remove the frontmatter or shebang from the file.
3. Ensure your cargo is a nightly build that supports -Zscript.

Example fix

# before
cargo run ./script.rs

# after (nightly)
cargo +nightly run -Zscript ./script.rs

fn check_script_feature_enabled(gctx: &GlobalContext) -> bool {
    gctx.cli_unstable().script
}

match parse_manifest(path, gctx) {
    Ok(m) => m,
    Err(e) if e.to_string().contains("requires `-Zscript`") => {
        eprintln!("Re-run with nightly cargo and -Zscript for embedded manifests");
        return Err(e);
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Running cargo against a .rs file that begins with a frontmatter (--- cargo ...) or shebang (#!/...) when -Zscript is not in the unstable flags. Detected via is_embedded(path) being true and gctx.cli_unstable().script being false.

Common situations: A user tries `cargo run script.rs` on a nightly feature file without -Zscript. A stable cargo toolchain encounters a single-file cargo script. The nightly flag was dropped from a wrapper command.

Related errors

• parsing ` ` requires `-Zscript
• not allowed in embedded manifests
• not implemented
• artifact-dir was not locked during clean
• cannot publish with `open-namespaces`

AI-assisted analysis of rust-lang/cargo@98a09e7e7d (2026-08-11). Data as JSON: /api/errors/f4a22a574dad5e24. Report an issue: GitHub.

Appendix: source

Thrown at src/workspace/parser/mod.rs:179

    mut document: toml::Spanned<toml::de::DeTable<'_>>,
) -> toml::Spanned<toml::de::DeTable<'static>> {
    document.get_mut().make_owned();
    // SAFETY: `DeTable::make_owned` ensures no borrows remain and the lifetime does not affect
    // layout
    unsafe {
        std::mem::transmute::<
            toml::Spanned<toml::de::DeTable<'_>>,
            toml::Spanned<toml::de::DeTable<'static>>,
        >(document)
    }
}

#[tracing::instrument(skip_all)]
fn read_toml_string(path: &Path, is_embedded: bool, gctx: &GlobalContext) -> CargoResult<String> {
    let mut contents = paths::read(path).map_err(|err| ManifestError::new(err, path.into()))?;
    if is_embedded {
        if !gctx.cli_unstable().script {
            anyhow::bail!("parsing `{}` requires `-Zscript`", path.display());
        }
        contents = embedded::expand_manifest(&contents)
            .map_err(|e| emit_frontmatter_diagnostic(e, &contents, path, gctx))?;
    }
    Ok(contents)
}

#[tracing::instrument(skip_all)]
fn parse_document(contents: &str) -> Result<toml::Spanned<toml::de::DeTable<'_>>, toml::de::Error> {
    toml::de::DeTable::parse(&contents)
}

#[tracing::instrument(skip_all)]
fn deserialize_toml(
    document: &toml::Spanned<toml::de::DeTable<'_>>,
) -> Result<manifest::TomlManifest, toml::de::Error> {
    let mut unused = BTreeSet::new();
    let deserializer = toml::de::Deserializer::from(document.clone());

View on GitHub (pinned to 98a09e7e7d)