sim/build.rs

// Builds the Leptos UI (ui/) to wasm and generates the JS bindings, so a plain `cargo run` works.
// The result lands in OUT_DIR/ui-pkg and is embedded into the binary by src/main.rs.
use std::path::{Path, PathBuf};
use std::process::Command;
use std::{env, fs};

fn main() {
    for p in ["ui/src", "ui/js", "ui/style.css", "ui/Cargo.toml"] {
        println!("cargo:rerun-if-changed={p}");
    }
    let out = PathBuf::from(env::var_os("OUT_DIR").expect("OUT_DIR"));
    let pkg = out.join("ui-pkg");
    let release = env::var("PROFILE").is_ok_and(|p| p == "release");

    ensure_wasm_target();

    // A separate target dir avoids deadlocking on the outer build's lock.
    let target_dir = out.join("ui-target");
    let mut cargo = Command::new(env::var_os("CARGO").unwrap_or_else(|| "cargo".into()));
    cargo
        .args([
            "build",
            "--manifest-path",
            "ui/Cargo.toml",
            "--target",
            "wasm32-unknown-unknown",
        ])
        .env("CARGO_TARGET_DIR", &target_dir)
        // Host rustflags (e.g. -fuse-ld=lld) break the wasm link.
        .env_remove("CARGO_ENCODED_RUSTFLAGS")
        .env_remove("RUSTFLAGS");
    if release {
        cargo.arg("--release");
    }
    let status = cargo
        .status()
        .expect("failed to run cargo for the ui crate");
    assert!(
        status.success(),
        "building ui/ failed (see the cargo output above); the wasm32-unknown-unknown target must be installed: rustup target add wasm32-unknown-unknown"
    );

    let profile = if release { "release" } else { "debug" };
    let wasm = target_dir
        .join("wasm32-unknown-unknown")
        .join(profile)
        .join("ui.wasm");
    let _ = fs::remove_dir_all(&pkg);
    wasm_bindgen_cli_support::Bindgen::new()
        .input_path(&wasm)
        .web(true)
        .expect("bindgen target")
        .out_name("ui")
        .typescript(false)
        .generate(&pkg)
        .expect("wasm-bindgen failed");
}

fn ensure_wasm_target() {
    let rustc = env::var_os("RUSTC").unwrap_or_else(|| "rustc".into());
    let sysroot = Command::new(rustc)
        .args(["--print", "sysroot"])
        .output()
        .ok()
        .and_then(|o| String::from_utf8(o.stdout).ok())
        .map(|s| PathBuf::from(s.trim()));
    let installed = sysroot
        .as_deref()
        .is_some_and(|s: &Path| s.join("lib/rustlib/wasm32-unknown-unknown").exists());
    if !installed {
        let _ = Command::new("rustup")
            .args(["target", "add", "wasm32-unknown-unknown"])
            .status();
    }
}