serai/substrate/runtime/build.rs

fn main() {
  use std::{path::PathBuf, fs, env, process::Command};

  // Prevent recursing infinitely
  if env::var("TARGET").unwrap() == "wasm32v1-none" {
    return;
  }

  // https://github.com/rust-lang/rust/issues/145491
  const ONE_45491: &str = "-C link-arg=--mllvm=-mcpu=mvp,--mllvm=-mattr=+mutable-globals";
  const WASM: &str = "-C link-arg=--export-table";
  const REQUIRED_BY_SUBSTRATE: &str = "--cfg substrate_runtime -C link-arg=--import-memory";
  const SAFETY: &str = "-C overflow-checks=true -C panic=abort";
  const COMPILATION: &str =
    "-C symbol-mangling-version=v0 -C embed-bitcode=false -C linker-plugin-lto=true";

  let profile = env::var("PROFILE").unwrap();
  let release = profile == "release";
  let rustflags = format!("{ONE_45491} {WASM} {REQUIRED_BY_SUBSTRATE} {SAFETY} {COMPILATION}");
  let rustflags = if release {
    format!("{rustflags} -C codegen-units=1 -C strip=symbols -C debug-assertions=false")
  } else {
    rustflags
  };

  let target_dir = PathBuf::from(env::var("OUT_DIR").unwrap()).join("target");

  let cargo_command = || {
    let cargo = env::var("CARGO").unwrap();
    let mut command = Command::new(&cargo);
    command
      .current_dir(env::var("CARGO_MANIFEST_DIR").unwrap())
      .env_clear()
      .env("PATH", env::var("PATH").unwrap())
      .env("CARGO", cargo)
      .env("RUSTC", env::var("RUSTC").unwrap())
      .env("RUSTFLAGS", &rustflags)
      .env("CARGO_TARGET_DIR", &target_dir);
    command
  };

  let workspace = {
    let workspace = cargo_command()
      .arg("locate-project")
      .arg("--workspace")
      .arg("--message-format")
      .arg("plain")
      .output()
      .unwrap();
    assert!(workspace.status.success());
    let mut workspace = PathBuf::from(String::from_utf8(workspace.stdout).unwrap().trim());
    assert_eq!(workspace.file_name().unwrap(), "Cargo.toml");
    assert!(workspace.pop());
    workspace
  };

  // Re-run anytime the workspace changes
  // TODO: Re-run anytime `Cargo.lock` or specifically the `src` folders change
  println!("cargo::rerun-if-changed={}", workspace.display());

  let mut command = cargo_command();
  command
    .arg("rustc")
    .arg("--package")
    .arg(env::var("CARGO_PKG_NAME").unwrap())
    .arg("--target")
    .arg("wasm32v1-none")
    .arg("--crate-type")
    .arg("cdylib")
    .arg("--no-default-features");
  if release {
    command.arg("--release");
  }
  assert!(command.status().unwrap().success());

  // Place the resulting WASM blob into the parent `target` directory
  {
    let wasm_file = env::var("CARGO_PKG_NAME").unwrap().replace('-', "_") + ".wasm";
    let src_file = target_dir.join("wasm32v1-none").join(&profile).join(&wasm_file);
    let dst_file = {
      let mut dst_dir = workspace.clone();
      // e.g. workspace/target/debug
      dst_dir.extend(["target", &profile]);
      let _ = fs::create_dir_all(&dst_dir);
      // e.g. workspace/target/debug/serai_runtime.wasm
      dst_dir.join(&wasm_file)
    };
    fs::copy(&src_file, &dst_file).unwrap();
  }
}