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

library `{}` cannot set the crate type of both `dylib` and `

Error message

library `{}` cannot set the crate type of both `dylib` and `cdylib`

What it means

Error "library `{}` cannot set the crate type of both `dylib` and `cdylib`" thrown in rust-lang/cargo.

Source

Thrown at src/workspace/parser/targets.rs:247

    let path = lib.path.as_ref().expect("previously normalized");
    let path = package_root.join(&path.0);

    // Per the Macros 1.1 RFC:
    //
    // > Initially if a crate is compiled with the `proc-macro` crate type
    // > (and possibly others) it will forbid exporting any items in the
    // > crate other than those functions tagged #[proc_macro_derive] and
    // > those functions must also be placed at the crate root.
    //
    // A plugin requires exporting plugin_registrar so a crate cannot be
    // both at once.
    let crate_types = match (lib.crate_types(), lib.proc_macro()) {
        (Some(kinds), _)
            if kinds.contains(&CrateType::Dylib.as_str().to_owned())
                && kinds.contains(&CrateType::Cdylib.as_str().to_owned()) =>
        {
            anyhow::bail!(format!(
                "library `{}` cannot set the crate type of both `dylib` and `cdylib`",
                name_or_panic(lib)
            ));
        }
        (Some(kinds), _) if kinds.contains(&"proc-macro".to_string()) => {
            warnings.push(format!(
                "library `{}` should only specify `proc-macro = true` instead of setting `crate-type`",
                name_or_panic(lib)
            ));
            if kinds.len() > 1 {
                anyhow::bail!("cannot mix `proc-macro` crate type with others");
            }
            vec![CrateType::ProcMacro]
        }
        (Some(kinds), _) => kinds.iter().map(|s| s.into()).collect(),
        (None, Some(true)) => vec![CrateType::ProcMacro],
        (None, _) => vec![CrateType::Lib],
    };

View on GitHub (pinned to 0e07a15537)

Solutions

1. Pick only one of `dylib` or `cdylib` in the `[lib] crate-type` list.
2. Split into separate crates if both dynamic library flavors are needed.

When it happens

Trigger: Thrown at src/workspace/parser/targets.rs:247 when the library encounters an invalid state.

Common situations: Occurs when a `[lib]` target lists both `dylib` and `cdylib` in `crate-type`. Choose one dynamic library crate type, as they are mutually exclusive.

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/101dad83b6438b9d.json. Report an issue: GitHub.