astrid-runtime/astrid · error

No Cargo build target selected. Set `[build] target = "wasm3

Error message

No Cargo build target selected. Set `[build] target = "wasm32-unknown-unknown"` (Astrid-canonical) or `wasm32-wasip2` in `.cargo/config.toml`, or set CARGO_BUILD_TARGET.

What it means

Astrid's WASM build refuses to guess a compilation target. rustc without an explicit --target builds a host binary, which would silently produce a native cdylib instead of a wasm module, so resolve_build_target requires either `[build] target` in .cargo/config.toml or the CARGO_BUILD_TARGET env var, and it must be a wasm triple.

Source

Thrown at crates/astrid-build/src/rust.rs:548

    }

    let mut value = config_flags.join(RUSTFLAGS_SEP);
    if !value.is_empty() {
        value.push_str(RUSTFLAGS_SEP);
    }
    value.push_str(GETRANDOM_CUSTOM_CFG);
    Some(("CARGO_ENCODED_RUSTFLAGS".to_owned(), value))
}

fn resolve_build_target(
    config_target: Option<String>,
    env_target: Option<String>,
) -> Result<String> {
    env_target
        .or(config_target)
        .filter(|target| !target.trim().is_empty())
        .ok_or_else(|| {
        anyhow::anyhow!(
            "No Cargo build target selected. Set `[build] target = \"wasm32-unknown-unknown\"` (Astrid-canonical) or `wasm32-wasip2` in `.cargo/config.toml`, or set CARGO_BUILD_TARGET."
        )
    })
}

/// Wrap a core wasm module into a Component Model component if it isn't
/// one already. `wasm32-unknown-unknown` (Astrid-canonical) produces a
/// core module with `wit-bindgen`'s component-type custom section
/// embedded; `wit_component::ComponentEncoder` consumes that section and
/// emits a real component. `wasm32-wasip2` builds skip this — cargo
/// already produces a component there.
fn ensure_component(wasm_path: &Path) -> Result<PathBuf> {
    let bytes =
        std::fs::read(wasm_path).context("Failed to read compiled WASM for component check")?;
    // Component magic: \0asm version=0x0d layer=0x01. Core magic:
    // \0asm version=0x01. The 4-byte version field at offset 4
    // distinguishes them.
    let is_component = bytes.len() >= 8 && &bytes[..4] == b"\0asm" && bytes[6] == 0x01;

View on GitHub (pinned to affd8760f4)

Solutions

1. Add `[build]\ntarget = "wasm32-unknown-unknown"` to `.cargo/config.toml` (Astrid-canonical)
2. Or set `target = "wasm32-wasip2"` if your capsule targets WASI
3. Export CARGO_BUILD_TARGET=wasm32-unknown-unknown in your shell/CI environment
4. Verify the value is not empty or whitespace-only

Example fix

// before (missing .cargo/config.toml)
// after
// .cargo/config.toml
[build]
target = "wasm32-unknown-unknown"

fn ensure_wasm_target() -> Result<(), String> {
    let t = std::env::var("CARGO_BUILD_TARGET").ok()
        .or_else(|| parse_cargo_config_build_target(".cargo/config.toml"));
    match t {
        Some(v) if !v.trim().is_empty() && v.starts_with("wasm32-") => Ok(()),
        _ => Err("set [build] target = \"wasm32-unknown-unknown\" in .cargo/config.toml".into()),
    }
}

fn has_wasm_target(v: &Option<String>) -> bool {
    v.as_deref().map_or(false, |t| !t.trim().is_empty() && t.starts_with("wasm32-"))
}

match compile_wasm(...) {
    Err(e) if e.to_string().contains("No Cargo build target selected") => {
        eprintln!("configure [build] target in .cargo/config.toml or CARGO_BUILD_TARGET");
    }
    other => other?,
}

When it happens

Trigger: Calling compile_wasm (via environment_target_overrides_capsule_config_target or directly) when neither `.cargo/config.toml` has `[build] target` nor the CARGO_BUILD_TARGET environment variable is set, or when the value present is empty/whitespace.

Common situations: Fresh clone of an Astrid capsule workspace without the .cargo/config.toml checked in; CI runner that doesn't inherit CARGO_BUILD_TARGET; developer removed the config file or relies on a shell alias that didn't export the var.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

• Cargo include table must contain a string path in {}
• Cargo include optional must be a boolean in {}
• failed to create wasmtime engine for hooks
• build_host_state
• installed WASM executable differs from its authority receipt

AI-assisted analysis of astrid-runtime/astrid@affd8760f4 (2026-09-09). Data as JSON: /api/errors/b3f70d371c0fa688. Report an issue: GitHub.