BoundaryML/baml · error

cargo build failed for pack ({} + {})

Error message

cargo build failed for pack ({} + {})

What it means

build_pack builds both the pack's CLI binary and host binary with a single `cargo build -p <cli_package> --bin <cli_bin> -p <host_package> --bin <host_bin>` invocation. If cargo exits non-zero, it bails naming both packages. Cargo's own diagnostics are already on stderr.

Source

Thrown at baml_language/crates/tools_size_gate/src/measure.rs:105

/// Build the CLI + pack host, then run `baml pack` on the fixture and
/// return the path to the produced standalone executable.
fn build_pack(workspace_root: &Path, name: &str, config: &ArtifactConfig) -> Result<PathBuf> {
    let pack = config.require_pack()?;

    // Build the CLI and the pack host in one release invocation. The host
    // binary must land next to the CLI in target/release so `baml pack`
    // resolves it locally (no GitHub download).
    eprintln!("  building {} + {}", pack.cli_package, pack.host_package);
    let status = Command::new("cargo")
        .arg("build")
        .arg("--release")
        .args(["-p", &pack.cli_package, "--bin", &pack.cli_bin])
        .args(["-p", &pack.host_package, "--bin", &pack.host_bin])
        .current_dir(workspace_root)
        .status()
        .context("failed to run cargo build for pack")?;
    if !status.success() {
        bail!(
            "cargo build failed for pack ({} + {})",
            pack.cli_package,
            pack.host_package
        );
    }

    run_baml_pack(workspace_root, name, pack)
}

/// Run the freshly built CLI's `baml pack` on the fixture, writing the
/// output to a deterministic path under `target/size-gate/`.
fn run_baml_pack(workspace_root: &Path, name: &str, pack: &PackConfig) -> Result<PathBuf> {
    let cli_path = workspace_root
        .join("target/release")
        .join(exe_filename(&pack.cli_bin));
    if !cli_path.exists() {
        bail!("pack CLI not found at {}", cli_path.display());
    }

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Read cargo's error output above the message to see which of the two targets failed
2. Build each target manually: cargo build -p <cli_package> --bin <cli_bin>, then the host
3. Verify package/bin names in the pack config match Cargo.toml
4. Fix the compile errors or test on a clean checkout

Example fix

// before: bin renamed in Cargo.toml but not in config
cli_bin = "baml-old"
// after
cli_bin = "baml"

let status = std::process::Command::new("cargo")
    .args(["build", "-p", cli_pkg, "--bin", cli_bin, "-p", host_pkg, "--bin", host_bin])
    .status()?;
if !status.success() { eprintln!("pack targets do not build; check bin/package names"); std::process::exit(1); }

if let Err(e) = measure() {
    if e.to_string().contains("cargo build failed for pack") {
        eprintln!("build the two pack targets manually to see which failed");
    }
    return Err(e);
}

When it happens

Trigger: Failure building either the CLI or host package/bin pair defined in the PackConfig during size-gate measure: compile errors in either crate, missing bins, or broken build scripts.

Common situations: Renamed bin or package targets in Cargo.toml without updating the pack config; compile errors introduced on the branch under test; host crate requiring a feature only available on certain platforms.

Understand the failure class

Background: "git command failed": what it means when a tool shells out to git and git exits non-zero — this error's family across 21 libraries.

Related errors

• cargo build failed for {package}
• cargo metadata failed
• cargo metadata failed
• packed artifact not found (expected at {})
• artifact not found: {} (expected at {})

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/4b271435464088a8. Report an issue: GitHub.