rust-lang/cargo · error · anyhow::Error

embedded manifest `{}` requires `-Zscript`

Error message

embedded manifest `{}` requires `-Zscript`

What it means

root_manifest detects via workspace::parser::is_embedded that the given path is an embedded manifest (a `.rs` file with a leading `//! ```cargo` block) but the `-Zscript` unstable flag is not enabled. Embedded manifests are part of cargo script (RFC 3424) and require the nightly `-Zscript` flag.

Source

Thrown at src/util/command_prelude.rs:1082

            anyhow::bail!(
                "manifest path `{}` is a directory but expected a file{suggested_path}",
                manifest_path.display()
            )
        } else if !path.ends_with("Cargo.toml") && !crate::workspace::parser::is_embedded(&path) {
            if gctx.cli_unstable().script {
                anyhow::bail!(
                    "the manifest-path must be a path to a Cargo.toml or script file: `{}`",
                    path.display()
                )
            } else {
                anyhow::bail!(
                    "the manifest-path must be a path to a Cargo.toml file: `{}`",
                    path.display()
                )
            }
        }
        if crate::workspace::parser::is_embedded(&path) && !gctx.cli_unstable().script {
            anyhow::bail!("embedded manifest `{}` requires `-Zscript`", path.display())
        }
        Ok(path)
    } else {
        find_root_manifest_for_wd(gctx.cwd())
    }
}

pub fn get_registry_candidates() -> CargoResult<Vec<clap_complete::CompletionCandidate>> {
    let gctx = new_gctx_for_completions()?;

    if let Ok(Some(registries)) =
        gctx.get::<Option<HashMap<String, HashMap<String, String>>>>("registries")
    {
        Ok(registries
            .keys()
            .map(|name| clap_complete::CompletionCandidate::new(name.to_owned()))
            .collect())
    } else {

View on GitHub (pinned to 0e07a15537)

Solutions

  1. Re-run with `-Zscript` on a nightly toolchain: `cargo +nightly run -Zscript --manifest-path script.rs`.
  2. If you did not mean to use a script, point `--manifest-path` at a real `Cargo.toml`.
  3. Configure your IDE/wrapper to pass `-Zscript` when invoking on script files.

Example fix

# before
cargo run --manifest-path script.rs

# after
cargo +nightly run -Zscript --manifest-path script.rs
Defensive patterns

Strategy: validation

Validate before calling

use std::path::Path;
fn require_script_flag_if_embedded(p: &Path, script_enabled: bool) -> Result<(), anyhow::Error> {
    if cargo::workspace::parser::is_embedded(p) && !script_enabled {
        anyhow::bail!("embedded manifest requires nightly cargo with -Zscript");
    }
    Ok(())
}
// script_enabled = gctx.cli_unstable().script

Type guard

fn needs_script_flag(p: &std::path::Path) -> bool {
    cargo::workspace::parser::is_embedded(p)
}

Try / catch

match root_manifest(Some(path), gctx) {
    Err(e) if e.to_string().contains("requires `-Zscript`") => {
        eprintln!("re-run with: cargo +nightly run -Zscript --manifest-path {path}");
        return Err(e);
    }
    r => r,
}

Prevention

When it happens

Trigger: Passing an embedded-manifest `.rs` script file as `--manifest-path` on a cargo build that was not launched with `-Zscript` (e.g. stable cargo, or nightly without the flag).

Common situations: Running a cargo script with stable cargo; nightly cargo invoked without `-Zscript`; a wrapper/IDE that passes the script path but not the unstable flag.

Related errors

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/fa464b7d46b1d42f.json. Report an issue: GitHub.