build.rs

use color_eyre::{
    eyre::{eyre, WrapErr},
    Result,
};
use std::env;
use std::fs;
use std::path::{Path, PathBuf};

fn main() -> color_eyre::Result<()> {
    let out_dir = PathBuf::from(env::var("OUT_DIR")?);

    // compile WASM modules
    let wasm_path = PathBuf::from("src/helloworld.wast");
    build_wasm(&wasm_path, out_dir)
        .with_context(|| format!("building WASM `{}` failed!", wasm_path.display()))?;

    // generate version info env vars
    gen_version()?;

    // also, re-run if the target triple changes.
    println!("cargo:rerun-if-changed=x86_64-mycelium.json");

    Ok(())
}

fn gen_version() -> Result<()> {
    use vergen::{vergen, Config, ShaKind};
    let mut config = Config::default();
    *config.git_mut().sha_kind_mut() = ShaKind::Both;
    // since this is a monorepo with multiple crates, vergen will use whatever
    // the latest git tag for generating semver, which might be a `cordyceps` or
    // `maitake` tag rather than a `mycelium` tag...
    *config.git_mut().semver_mut() = false;
    vergen(config).map_err(|v| eyre!("vergen error: {v}"))
}

fn build_wasm(wasm: impl AsRef<Path>, out_dir: impl AsRef<Path>) -> Result<()> {
    let wasm = wasm.as_ref();
    // Build our helloworld.wast into binary.
    let binary = wat::parse_file(wasm)?;
    let file_stem = wasm
        .file_stem()
        .ok_or_else(|| eyre!("wast file path has no file stem"))?;
    fs::write(
        out_dir.as_ref().join(file_stem).with_extension("wasm"),
        binary,
    )?;

    println!("cargo:rerun-if-changed={}", wasm.display());
    Ok(())
}