zed-industries/zed · error

failed to build extension {}

Error message

failed to build extension {}

What it means

The Rust compile step of extension building failed: the builder runs 'cargo build --target wasm32-wasip2' (RUST_TARGET) inside the extension dir with sccache disabled (RUSTC_WRAPPER=""), and a non-zero exit status triggers this bail with cargo's stderr appended. This is the generic wrapper for any Rust compile failure in the extension crate itself.

Source

Thrown at crates/extension/src/extension_builder.rs:225

    ) -> anyhow::Result<()> {
        self.install_rust_wasm_target_if_needed().await?;

        let cargo_toml_content = fs::read_to_string(extension_dir.join("Cargo.toml"))?;
        let cargo_toml: CargoToml = toml::from_str(&cargo_toml_content)?;

        log::info!("compiling Rust crate for extension {extension_dir:?}");
        let output = util::command::new_command("cargo")
            .args(["build", "--target", RUST_TARGET])
            .args(options.release.then_some("--release"))
            .arg("--target-dir")
            .arg(extension_dir.join("target"))
            // WASI builds do not work with sccache and just stuck, so disable it.
            .env("RUSTC_WRAPPER", "")
            .current_dir(extension_dir)
            .output()
            .await
            .context("running `cargo`")?;
        anyhow::ensure!(
            output.status.success(),
            "failed to build extension {}",
            String::from_utf8_lossy(&output.stderr)
        );

        log::info!("compiled Rust crate for extension {extension_dir:?}");

        let mut wasm_path = PathBuf::from(extension_dir);
        wasm_path.extend([
            "target",
            RUST_TARGET,
            if options.release { "release" } else { "debug" },
            &cargo_toml
                .package
                .name
                // The wasm32-wasip2 target normalizes `-` in package names to `_` in the resulting `.wasm` file.
                .replace('-', "_"),
        ]);

View on GitHub (pinned to 9d272b0363)

Solutions

1. Reproduce locally in the extension directory to see the full log: 'cargo build --target wasm32-wasip2' (the bail message already carries cargo's stderr - read it first)
2. Fix the Rust errors it reports; for wasm-incompatible APIs switch to Zed's extension APIs (zed::fs, zed::Command via the language registry) instead of std::process/std::fs
3. Ensure the target exists: 'rustup target add wasm32-wasip2' (the builder normally auto-installs it - see errors 273-275)
4. Remove or align any rust-toolchain/rust-toolchain.toml in the extension dir that pins a toolchain without wasip2
5. Check dependency versions compile for wasm: 'cargo check --target wasm32-wasip2' in CI for the extension

Example fix

// before: extension code that cannot build for wasm32-wasip2
let output = std::process::Command::new("rg").arg("--version").output()?;

// after: use the host API Zed exposes to extensions instead
let output = zed::Command::new("rg").args(["--version"]).output().await?;

// Fail fast in CI before invoking the Zed builder
cargo check --target wasm32-wasip2 --manifest-path ext/Cargo.toml

match builder.compile_extension(&dir, &mut manifest, options, fs.clone()).await {
    Ok(()) => Ok(()),
    Err(err) if err.to_string().contains("failed to build extension") => {
        // err already carries cargo's stderr; surface it verbatim to the developer
        Err(err.context("cargo could not build the extension for wasm32-wasip2 - fix the reported Rust errors"))
    }
    Err(err) => Err(err),
}

When it happens

Trigger: Any error cargo reports while building the extension crate for wasm32-wasip2: syntax/type errors in the extension code, a dependency that fails to compile for wasm, missing wasm32-wasip2 std (target not installed), lock-file/edition problems, or a rust-toolchain override in the extension dir selecting an incompatible toolchain.

Common situations: Extension code that compiles on desktop but uses APIs unavailable under wasm32-wasip2 (e.g. std::process::Command, raw file paths outside zed::fs), a dependency pulling in tokio full features or C code without wasm support, CI where the wasm target was never added, or a pinned old toolchain that lacks the wasip2 target.

Related errors

• DAP returned IPv6 host {addr}, which the v0.6.0 extension AP
• extension {} has invalid zed:api-version section: {:?}
• failed to fetch '{url}': status code {}
• Unknown settings category: {}
• failed to fetch '{url}': status code {}

AI-assisted analysis of zed-industries/zed@9d272b0363 (2026-09-12). Data as JSON: /api/errors/1b8e7a041208da99. Report an issue: GitHub.