What causes "'{}' is not a valid artifact specifier" in rust-lang/cargo?

Use one of the supported kinds: bin, cdylib, staticlib, or bin: .

' ' is not a valid artifact specifier

Error message

'{}' is not a valid artifact specifier

What it means

ArtifactKind::parse accepts exactly: `bin` (all binaries), `cdylib`, `staticlib`, or `bin:<name>` (a specific binary). Any other artifact kind string yields this error. This parses the `artifact = "..."` / `artifact = [...]` field of a dependency declaration.

Solutions

Use one of the supported kinds: bin, cdylib, staticlib, or bin:<name>.
If you need a different library type, build it as a normal dependency without the artifact field.
Re-read the dependency.artifact docs to confirm supported values.

Example fix

# before (Cargo.toml)
# [dependencies]
# foo = { version = "1", artifact = "dylib" }

# after
# [dependencies]
# foo = { version = "1", artifact = "cdylib" }

Defensive patterns

Strategy: validation

Validate before calling

fn parse_artifact_kind(kind: &str) -> Result<(), String> {
    let ok = matches!(kind, "bin" | "cdylib" | "staticlib") || kind.starts_with("bin:");
    if ok { Ok(()) } else { Err(format!("'{kind}' is not a valid artifact specifier")) }
}

Type guard

fn is_valid_artifact_kind(kind: &str) -> bool {
    matches!(kind, "bin" | "cdylib" | "staticlib") || kind.starts_with("bin:")
}

Prevention

Restrict artifact kinds to bin, cdylib, staticlib, or bin:<name>.
Add a manifest lint that rejects unknown artifact values before publish.
Do not confuse target crate-types (lib, rlib, dylib, proc-macro) with dependency artifact kinds.

When it happens

Trigger: Declaring a dependency with an unsupported artifact kind in Cargo.toml, e.g. `artifact = "lib"`, `artifact = "dylib"`, `artifact = "proc-macro"`.

Common situations: Assuming any crate-type is a valid artifact; typo in the kind; confusing target crate-types with dependency artifact kinds.

Related errors

AI-assisted analysis of rust-lang/cargo@98a09e7e7d (2026-08-11). Data as JSON: /api/errors/d828e9b48c94aa58. Report an issue: GitHub.

Appendix: source

Thrown at src/workspace/dependency.rs:648

    pub fn as_str(&self) -> Cow<'static, str> {
        match *self {
            ArtifactKind::SelectedBinary(name) => format!("bin:{}", name.as_str()).into(),
            _ => self.crate_type().into(),
        }
    }

    pub fn parse(kind: &str) -> CargoResult<Self> {
        Ok(match kind {
            "bin" => ArtifactKind::AllBinaries,
            "cdylib" => ArtifactKind::Cdylib,
            "staticlib" => ArtifactKind::Staticlib,
            _ => {
                return kind
                    .strip_prefix("bin:")
                    .map(|bin_name| ArtifactKind::SelectedBinary(bin_name.into()))
                    .ok_or_else(|| {
                        anyhow::anyhow!("'{}' is not a valid artifact specifier", kind)
                    });
            }
        })
    }

    fn validate(kinds: Vec<ArtifactKind>) -> CargoResult<Vec<ArtifactKind>> {
        if kinds.iter().any(|k| matches!(k, ArtifactKind::AllBinaries))
            && kinds
                .iter()
                .any(|k| matches!(k, ArtifactKind::SelectedBinary(_)))
        {
            anyhow::bail!(
                "Cannot specify both 'bin' and 'bin:<name>' binary artifacts, as 'bin' selects all available binaries."
            );
        }
        let mut kinds_without_dupes = kinds.clone();
        kinds_without_dupes.sort();
        kinds_without_dupes.dedup();

View on GitHub (pinned to 98a09e7e7d)