nixide/nixide-sys/build.rs

use std::env;
use std::fs;
use std::iter;
use std::path::PathBuf;

use bindgen::RustEdition;
use bindgen::callbacks::{ItemKind, ParseCallbacks};
use heck::ToSnekCase;
use heck::ToUpperCamelCase;
use itertools::Itertools;

#[derive(Debug)]
struct DoxygenCallbacks;

impl ParseCallbacks for DoxygenCallbacks {
    fn process_comment(&self, comment: &str) -> Option<String> {
        match doxygen_bindgen::transform(comment) {
            Ok(res) => Some(res),
            Err(err) => {
                println!("cargo::warning=Problem processing doxygen comment: {comment}\n{err}");
                None
            },
        }
    }
}

#[inline]
fn strip_variant_prefix(
    prefix: &'static str,
    enum_name: &str,
    variant: &str,
) -> Result<String, String> {
    variant
        .strip_prefix(prefix)
        .map(str::to_owned)
        .ok_or(format!(
            "[bindfmt] enum {enum_name} expected prefix \"{prefix}\" but got {}",
            &variant
        ))
}

/// Bindfmt is just the name im giving to the callbacks
/// that handle renaming C/C++ tokens.
#[derive(Debug)]
struct BindfmtCallbacks;

impl ParseCallbacks for BindfmtCallbacks {
    fn enum_variant_name(
        &self,
        _enum_name: Option<&str>,
        _original_variant_name: &str,
        _variant_value: bindgen::callbacks::EnumVariantValue,
    ) -> Option<String> {
        let variant = _original_variant_name.to_upper_camel_case();

        _enum_name.map(|enum_name| match enum_name.to_upper_camel_case().as_ref() {
            "NixVerbosity" => strip_variant_prefix("NixLvl", enum_name, &variant).unwrap(),
            "NixErr" => strip_variant_prefix("NixErr", enum_name, &variant)
                .or_else(|_| strip_variant_prefix("Nix", enum_name, &variant))
                .unwrap(),
            "ValueType" => strip_variant_prefix("NixType", enum_name, &variant)
                .or_else(|_| strip_variant_prefix("N", enum_name, &variant))
                .unwrap(),
            _ => variant,
        })
    }

    fn item_name(&self, _item_info: bindgen::callbacks::ItemInfo) -> Option<String> {
        Some(match _item_info.kind {
            ItemKind::Type => _item_info.name.to_upper_camel_case(),
            _ => _item_info.name.to_snek_case(),
        })
    }

    fn include_file(&self, _filename: &str) {
        eprintln!("[debug] including file: {}", _filename);
    }
}

const FEATURES: &[&'static str] = &[
    #[cfg(feature = "nix-util-c")]
    "util",
    #[cfg(feature = "nix-store-c")]
    "store",
    #[cfg(feature = "nix-expr-c")]
    "expr",
    #[cfg(feature = "nix-fetchers-c")]
    "fetchers",
    #[cfg(feature = "nix-flake-c")]
    "flake",
    #[cfg(feature = "nix-main-c")]
    "main",
];

fn main() {
    let libs: Vec<pkg_config::Library> = FEATURES
        .iter()
        .map(|&feature| {
            let name = &format!("nix-{feature}-c");
            pkg_config::probe_library(name).expect(&format!("Unable to find .pc file for {}", name))
        })
        .collect();

    #[allow(unused)]
    let include_paths: Vec<PathBuf> = libs
        .clone()
        .into_iter()
        .map(|lib| lib.include_paths)
        .flatten()
        .chain(iter::once(fs::canonicalize("./libnixide-c").unwrap()))
        .unique()
        .collect();

    #[allow(unused)]
    let link_paths: Vec<PathBuf> = libs
        .clone()
        .into_iter()
        .map(|lib| lib.link_files)
        .flatten()
        .unique()
        .collect();

    // build the libnixide-c extension
    cc::Build::new()
        // .cargo_output(true)
        // .cargo_warnings(true)
        // .cargo_metadata(true)
        // .cargo_debug(cfg!(debug_assertions))
        .cpp(true)
        .std("c++23") // libnix compiles against `-std=c++23`
        .cpp_link_stdlib("c++") // libstdc++ for GNU, c++ for Clang
        .opt_level((!cfg!(debug_assertions)) as u32 * 3)
        .files(FEATURES.iter().map(|&feature| format!("libnixide-c/nixide_api_{feature}.cc")))
        .includes(&include_paths)
        .compile("nixide-c"); // libnixide-c

    let clang_args: Vec<String> = vec!["-x", "c++", "-std=c++23"]
        .into_iter()
        .map(|s: &str| s.to_owned())
        .chain(include_paths.iter().map(|p| format!("-I{}", p.display())))
        .collect();
    dbg!(&clang_args);
    
    let mut builder = bindgen::Builder::default()
        .rust_edition(RustEdition::Edition2024)
        .clang_args(clang_args)
        // Add `doxygen_bindgen` callbacks
        .parse_callbacks(Box::new(DoxygenCallbacks))
        .parse_callbacks(Box::new(BindfmtCallbacks))
        .parse_callbacks(Box::new(bindgen::CargoCallbacks::new()))
        // Format generated bindings with rustfmt
        .formatter(bindgen::Formatter::Rustfmt)
        .rustfmt_configuration_file(std::fs::canonicalize("rustfmt.toml").ok())
        // Control allow/block listing
        .allowlist_recursively(true) 
        .allowlist_file(r".*nix_api_[a-z]+(/[a-z_]+)?\.h")
        .allowlist_file(r".*nixide_api_[a-z]+(/[a-z_]+)?\.h")

        // .layout_tests(false) // DEBUG
        .use_core() // use ::core instead of ::std
        .ctypes_prefix("::core::ffi") // use ::core::ffi instead of ::std::os::raw
        .time_phases(true)
        // Wrap all unsafe operations in unsafe blocks
        .wrap_unsafe_ops(true)
        .trust_clang_mangling(true)
        .respect_cxx_access_specs(true)
        .default_enum_style(bindgen::EnumVariation::Rust { non_exhaustive: false })
        // .translate_enum_integer_types(false)
        .size_t_is_usize(true)
        // .use_distinct_char16_t(false) // DEBUG
        .generate_comments(false)
        .generate_cstr(true) // use &CStr instead of &[u8]
        .fit_macro_constants(false)
        .explicit_padding(true)
        // .enable_cxx_namespaces()
        // .represent_cxx_operators(false) // DEBUG
        .enable_function_attribute_detection()
        .raw_line("/** These bindings were auto-generated for the Nixide project (https://github.com/cry128/nixide) */");

    // Register the input headers we would like to generate bindings for
    builder = FEATURES
        .iter()
        .map(|&feature| {
            let path = format!("include/nix-{feature}.h");
            assert!(fs::exists(&path).unwrap());
            // Invalidate the built crate if the binding headers change
            println!("cargo::rerun-if-changed={path}");
            path
        })
        .fold(builder, |builder, path| builder.header(path));

    // Write the bindings to the $OUT_DIR/bindings.rs file
    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());

    let bindings = builder.generate().expect("Unable to generate bindings");
    bindings
        .write_to_file(out_path.join("bindings.rs"))
        .expect("Couldn't write bindings!");
}