rust-lang/cargo · error

library target names cannot contain hyphens

Error message

library target names cannot contain hyphens: {}

What it means

A library target's explicit `name` (the `[lib] name` field, not the package name) cannot contain hyphens, because it maps to a Rust crate identifier and module path. Cargo would normally derive the underscore form from the package name, but an explicit hyphenated lib name is rejected at targets.rs:1157-1159.

Solutions

1. Replace hyphens with underscores: `name = "my_lib"`.
2. Omit the `[lib] name` field to let Cargo derive it from the package name automatically.
3. Keep the package name hyphenated; only the lib `name` must use underscores.

Example fix

# before
[lib]
name = "my-lib"

# after
[lib]
name = "my_lib"

fn lib_name_valid(name: &str) -> bool {
    !name.contains('-')
}
// enforce underscores for explicit `[lib] name` values

When it happens

Trigger: Cargo.toml has `[lib] name = "my-lib"`. The `name.contains('-')` check fires.

Common situations: Setting `[lib] name` to match a hyphenated package name verbatim. Renaming a lib target without converting hyphens. Confusing the package name (hyphens allowed) with the lib crate name (underscores only).

Related errors

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• cannot specify both `metabuild` and `build`
• found build scripts with duplicate file stems, but all…
• found duplicate name , but all targets must have a unique…

AI-assisted analysis of rust-lang/cargo@eb98b54bc9 (2026-08-11). Data as JSON: /api/errors/4400322375732fed. Report an issue: GitHub.

Appendix: source

Thrown at src/workspace/parser/targets.rs:1152

fn validate_build_name(build: &str) -> CargoResult<()> {
    if Path::new(build).file_stem().is_none() {
        anyhow::bail!("invalid `package.build` file name");
    }
    Ok(())
}

fn name_or_panic(target: &TomlTarget) -> &str {
    target
        .name
        .as_deref()
        .unwrap_or_else(|| panic!("target name is required"))
}

fn validate_lib_name(target: &TomlTarget, warnings: &mut Vec<String>) -> CargoResult<()> {
    validate_target_name(target, TARGET_KIND_HUMAN_LIB, TARGET_KIND_LIB, warnings)?;
    let name = name_or_panic(target);
    if name.contains('-') {
        anyhow::bail!("library target names cannot contain hyphens: {}", name)
    }

    Ok(())
}

fn validate_bin_name(bin: &TomlTarget, warnings: &mut Vec<String>) -> CargoResult<()> {
    validate_target_name(bin, TARGET_KIND_HUMAN_BIN, TARGET_KIND_BIN, warnings)?;
    let name = name_or_panic(bin).to_owned();
    if restricted_names::is_conflicting_artifact_name(&name) {
        anyhow::bail!(
            "the binary target name `{name}` is forbidden, \
                 it conflicts with cargo's build directory names",
        )
    }

    Ok(())
}

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