rust-lang/rust · error

TOOLCHAIN_NAME

Error message

TOOLCHAIN_NAME

What it means

This panic fires in the `cargo-clif` wrapper script for the Cranelift codegen backend. The script uses `option_env!("TOOLCHAIN_NAME")` to read the toolchain name at compile time, then `.expect("TOOLCHAIN_NAME")` at runtime. `TOOLCHAIN_NAME` is a build-time environment variable that must be set when the wrapper script itself is compiled (by the cg_clif build system). If it's not set, the `option_env!` yields `None` and the script panics on launch.

Source

Thrown at compiler/rustc_codegen_cranelift/scripts/cargo-clif.rs:37

    }
    if let Some(name) = option_env!("BUILTIN_BACKEND") {
        rustflags.push(format!("-Zcodegen-backend={name}"));
    } else {
        let dylib = sysroot.join("lib").join(
            env::consts::DLL_PREFIX.to_string()
                + "rustc_codegen_cranelift"
                + env::consts::DLL_SUFFIX,
        );
        rustflags.push(format!("-Zcodegen-backend={}", dylib.to_str().unwrap()));
    }
    rustflags.push("--sysroot".to_owned());
    rustflags.push(sysroot.to_str().unwrap().to_owned());

    let cargo = if let Some(cargo) = option_env!("CARGO") {
        cargo
    } else {
        // Ensure that the right toolchain is used
        env::set_var("RUSTUP_TOOLCHAIN", option_env!("TOOLCHAIN_NAME").expect("TOOLCHAIN_NAME"));
        "cargo"
    };

    let mut args = env::args().skip(1).collect::<Vec<_>>();
    if args.get(0).map(|arg| &**arg) == Some("clif") {
        // Avoid infinite recursion when invoking `cargo-clif` as cargo subcommand using
        // `cargo clif`.
        args.remove(0);
    }

    let args: Vec<_> = match args.get(0).map(|arg| &**arg) {
        Some("jit") => {
            rustflags.push("-Cprefer-dynamic".to_owned());
            args.remove(0);
            IntoIterator::into_iter(["rustc".to_string()])
                .chain(args)
                .chain([
                    "--".to_string(),

View on GitHub (pinned to 7088e4b63a)

Solutions

1. Use the official build system (`./y.rs prepare && ./y.rs build`) which sets `TOOLCHAIN_NAME` during compilation.
2. Set `TOOLCHAIN_NAME` manually before building: `TOOLCHAIN_NAME=stage2 cargo build --manifest-path scripts/Cargo.toml`.
3. If `CARGO` env var is set, the script bypasses the toolchain check — set `CARGO` to your cargo binary as a workaround.
4. Follow the cg_clif README's installation instructions exactly; do not copy binaries built without the build system.

Example fix

# before (manual build → TOOLCHAIN_NAME not set → panic)
cargo build --manifest-path compiler/rustc_codegen_cranelift/scripts/Cargo.toml
./target/debug/cargo-clif build

# after (use the official build system)
cd compiler/rustc_codegen_cranelift
./y.rs prepare && ./y.rs build
# then use the installed cargo-clif

// Check before building that TOOLCHAIN_NAME will be available.
// In the build script or CI:
// test -n "$TOOLCHAIN_NAME" || { echo "TOOLCHAIN_NAME not set"; exit 1; }
// Or check at Rust compile time (in the script's build.rs):
// fn main() {
//     if option_env!("TOOLCHAIN_NAME").is_none() && option_env!("CARGO").is_none() {
//         panic!("Set TOOLCHAIN_NAME or CARGO before building cargo-clif");
//     }
// }

When it happens

Trigger: Running `cargo-clif` (the Cranelift backend's cargo wrapper) when the binary was compiled without the `TOOLCHAIN_NAME` environment variable set. This happens when the wrapper is built outside the official cg_clif build system (e.g., copied manually, built with a bare `cargo build`, or installed via a method that bypasses `build_system/`).

Common situations: Installing rustc_codegen_cranelift by manually running `cargo build` in the scripts directory instead of using the project's `build_system/` / `y.rs` build tool. Also happens if the build system's environment setup is incomplete or the toolchain name variable was removed in a refactor.

Related errors

• TOOLCHAIN_NAME
• TOOLCHAIN_NAME
• Failed to spawn `as`.
• Failed to wait for `as`.
• cannot allocate registers

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/aa36c463641636b4. Report an issue: GitHub.