build.rs

#[cfg(feature = "enzyme")]
mod enzyme {
    use bindgen::{BindgenError, Bindings, Builder};
    use std::{env, path::PathBuf};

    fn compile_enzyme(llvm_dir: String) -> (String, String) {
        let dst = cmake::Config::new("Enzyme/enzyme")
            .define("ENZYME_STATIC_LIB", "ON")
            .define("ENZYME_CLANG", "OFF")
            .define("LLVM_DIR", llvm_dir)
            .define(
                "CMAKE_CXX_FLAGS",
                "-Wno-comment -Wno-deprecated-declarations",
            )
            .build();
        let dst_disp = dst.display();
        let lib_dir = format!("{}/lib", dst_disp);
        let inc_dir = "Enzyme/enzyme".to_string();
        (lib_dir, inc_dir)
    }

    fn enzyme_bindings(inc_dirs: &[String]) -> Result<Bindings, BindgenError> {
        let mut builder = Builder::default()
            .header("wrapper.h")
            .generate_comments(false)
            .clang_arg("-x")
            .clang_arg("c++");

        // add include dirs
        for dir in inc_dirs {
            builder = builder.clang_arg(format!("-I{}", dir))
        }
        builder.generate()
    }

    pub fn enzyme_main() {
        // get env vars matching DEP_LLVM_*_LIBDIR regex
        let llvm_dirs: Vec<_> = env::vars()
            .filter(|(k, _)| k.starts_with("DEP_LLVM_") && k.ends_with("_LIBDIR"))
            .collect();
        // take first one
        let llvm_lib_dir = llvm_dirs
            .first()
            .expect("DEP_LLVM_*_LIBDIR not set")
            .1
            .clone();
        let llvm_env_key = llvm_dirs.first().unwrap().0.clone();
        let llvm_version = &llvm_env_key["DEP_LLVM_".len()..(llvm_env_key.len() - "_LIBDIR".len())];
        dbg!(llvm_version);

        // replace last "lib" with "include"
        let llvm_inc_dir = llvm_lib_dir
            .chars()
            .take(llvm_lib_dir.len() - 3)
            .collect::<String>()
            + "include";

        // compile enzyme
        let (libdir, incdir) = compile_enzyme(llvm_lib_dir.clone());
        let libnames = [format!("EnzymeStatic-{}", llvm_version)];

        // bind enzyme api
        let bindings_rs = PathBuf::from(env::var("OUT_DIR").unwrap()).join("bindings.rs");
        let bindings =
            enzyme_bindings(&[llvm_inc_dir, incdir]).expect("Couldn't generate bindings!");
        bindings
            .write_to_file(bindings_rs)
            .expect("Couldn't write file bindings.rs!");

        println!("cargo:rustc-link-search=native={}", libdir);
        println!("cargo:rustc-link-search=native={}", llvm_lib_dir);
        for libname in libnames.iter() {
            println!("cargo:rustc-link-lib={}", libname);
        }
        println!("cargo:rustc-link-lib=LLVMDemangle");
        println!("cargo:rerun-if-changed=wrapper.h");
    }
}

fn main() {
    #[cfg(feature = "enzyme")]
    enzyme::enzyme_main();
}