rust-lang/cargo · error

could not find specification for target `{target}`. Depend

Error message

could not find specification for target `{target}`.
  Dependency `{dependency}` requires to build for target `{target}`.

What it means

In get_sysroot_target_libdir (compilation.rs:488-515), Cargo needs target info for each CompileKind in the build. If `bcx.target_data.get_info(kind)` returns None, the target specification could not be loaded — typically the target triple is not installed or is unknown — and Cargo bails naming the missing target and the dependency that forced building for it.

Source

Thrown at src/compiler/compilation.rs:506

fn get_sysroot_target_libdir(
    bcx: &BuildContext<'_, '_>,
) -> CargoResult<HashMap<CompileKind, PathBuf>> {
    bcx.all_kinds
        .iter()
        .map(|&kind| {
            let Some(info) = bcx.target_data.get_info(kind) else {
                let target = match kind {
                    CompileKind::Host => "host".to_owned(),
                    CompileKind::Target(s) => s.short_name().to_owned(),
                };

                let dependency = bcx
                    .unit_graph
                    .iter()
                    .find_map(|(u, _)| (u.kind == kind).then_some(u.pkg.summary().package_id()))
                    .unwrap();

                anyhow::bail!(
                    "could not find specification for target `{target}`.\n  \
                    Dependency `{dependency}` requires to build for target `{target}`."
                )
            };

            Ok((kind, info.sysroot_target_libdir.clone()))
        })
        .collect()
}

fn target_runner(
    bcx: &BuildContext<'_, '_>,
    kind: CompileKind,
) -> CargoResult<Option<(PathBuf, Vec<String>)>> {
    if let Some(runner) = bcx.target_data.target_config(kind).runner.as_ref() {
        let path = runner.val.path.clone().resolve_program(bcx.gctx);
        return Ok(Some((path, runner.val.args.clone())));
    }

View on GitHub (pinned to 0e07a15537)

Solutions

1. Install the target: `rustup target add <triple>`.
2. Fix the triple spelling in `--target`, `[build] target`, or `target.<triple>.*` config.
3. If using a custom JSON target, pass `--target path/to/target.json` and ensure the file exists.
4. Remove/adjust the dependency that forces the unavailable target.

Example fix

// before
$ cargo build --target aarch64-unknown-linux-gnu
error: could not find specification for target `aarch64-unknown-linux-gnu`.

// after
$ rustup target add aarch64-unknown-linux-gnu && cargo build --target aarch64-unknown-linux-gnu

let installed: Vec<String> = rustup_installed_targets();
if !installed.iter().any(|t| t == target) && !Path::new(target).is_file() {
    return Err(format!("target `{target}` not installed/found; rustup target add {target}"));
}

fn target_available(triple: &str, installed: &[String], json_exists: bool) -> bool {
    installed.iter().any(|t| t == triple) || json_exists
}

When it happens

Trigger: A dependency or `--target <triple>` requires a target whose std/component is not installed, or whose custom target JSON cannot be found/parsed. The dependency's build-resolver forces the kind, but no target spec is registered for it.

Common situations: Cross-compiling without `rustup target add <triple>`; a dependency with a `target.<triple>.dependencies` entry for an unavailable target; a typo in the triple; a custom target JSON path that does not resolve.

Related errors

• output of --print={request} missing when learning about targ
• cannot produce {} for `{}` as the target `{}` does not suppo
• cannot compile `{}` as the target `{}` does not support any
• malformed output when learning about crate-type {} informati
• target must support `bin`

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/a252d45af7ada73c.json. Report an issue: GitHub.