rusty-cheddar

A rustc compiler plugin to automatically generate C header files from Rust source files.

Usage

Compiler plugins have not yet been stabilised so you must use a nightly compiler. If you wish to build against stable Rust as well then I suggest multirust or multirust-rs.

rusty-cheddar targets C99 or later (for sane single line comments and use of stdint.h and stdbool.h), if you really really really really really have to use an older standard then please open an issue at the repo and I will begrudgingly figure out how to implement support for it (after arguing with you lots and lots).

Using rusty-cheddar is very simple, first add the dependency to your Cargo.toml

[dependencies]
rusty-cheddar = "0.1"

then at the top of your lib.rs

#![feature(plugin)]
#![plugin(cheddar)]

rusty-cheddar will then create a cheddar.h file in your working directory containing the generated header file. Note that rusty-cheddar emits very few warnings, it is up to the programmer to write a library which can be correctly called from C.

You can optionally specify a path for the header file using plugin arguments. The last argument is the name of the header file without any extensions and any other arguments are directories which do not have to exist.

#![plugin(cheddar(my_header))]

This will create my_header.h in the current working directory.

#![plugin(cheddar(target, include, my_header))]

This will first create the directories in target/include if they don't exist and will then create my_header.h in target/include.

In the examples below, boilerplate has been omitted from the header.

Typedefs

rusty-cheddar converts pub type A = B into typedef B A;. Types containing generics are ignored.

Rust:

type UInt32 = u32;
pub type UInt64 = u64;
pub type MyOption<T> = Option<T>

Header:

// Some boilerplate omitted.
typedef uint64_t UInt64;
// Some more boilerplate omitted.

Enums

rusty-cheddar will convert public enums which are marked #[repr(C)]. If the enum is generic or contains tuple or struct variants then cheddar will fail. rusty-cheddar should correctly handle explicit discriminants.

Rust:

#[repr(C)]
pub enum Colours {
    Red = -6,
    Blue,
    Green = 7,
    Yellow,
}

// This would fail is it was #[repr(C)].
pub enum Tastes<T> {
    Savoury,
    Sweet,
}

// This would fail if it was public.
#[repr(C)]
enum Units {
    Kg(f64),
    M(f64),
    S(f64),
    A(f64),
    K(f64),
    Mol(f64),
    Cd(f64),
}

Header:

// Some boilerplate omitted.
typedef enum Colours {
        Red = -6,
        Blue,
        Green = 7,
        Yellow,
} Colours;
// Some more boilerplate omitted.

Structs

Structs are handled very similarly to enums, they must be public, marked #[repr(C)], and they must not contain generics (this currently only checked at the struct-level, generic fields are not checked).

Rust:

#[repr(C)]
pub struct Person {
    age: i32,
    height: f64,
    weight: f64,
}

Header:

// Some boilerplate omitted.
typedef struct Person {
        int32_t age;
        double height;
        double weight;
} Person;
// Some more boilerplate omitted.

Functions

For rusty-cheddar to pick up on a function declaration it must be public, marked #[no_mangle] and have one of the following ABIs:

• C
• Cdecl
• Stdcall
• Fastcall
• System

I'm not totally up to speed on calling conventions so if you believe one of these has been including in error, or if one has been omitted, then please open an issue at the repo.

rusty-cheddar will fail on functions which are marked as diverging (-> !).

Rust:

use std::ops::Add;

#[no_mangle]
pub extern fn hello() {
    println!("Hello!");
}

fn add<O, R, L: Add<R, Output=O>>(l: L, r: R) -> O {
    l + r
}

#[no_mangle]
#[allow(non_snake_case)]
pub extern fn MyAdd_add_u8(l: u8, r: u8) -> u8 {
    add(l, r)
}

#[no_mangle]
#[allow(non_snake_case)]
pub extern fn MyAdd_add_u16(l: u16, r: u16) -> u16 {
    add(l, r)
}

Header:

// Some boilerplate omitted.
void hello();

uint8_t MyAdd_add_u8(uint8_t l, uint8_t r);

uint16_t MyAdd_add_u16(uint16_t l, uint16_t r);
// Some more boilerplate omitted.

Type Conversions

As of commit 976d215ad6c4cdc370dbda161f33fb8b4e02bcad the function which converts types handles all numeric types and any user defined types correctly. Types defined in other crates (notably libc and std) are not handled correctly and function pointers are not handled correctly.

rusty-cheddar currently does not handle type paths (e.g. mymod::MyType), instead they must be useed first:

// pub type MyCType = mymod::MyType;  // This will put `typedef mymod::MyType MyCType;` into the header.
use mymod::MyType;
pub type MyCType = MyType;

The very important exception to this rule is libc, types used from libc must be qualified (e.g. libc::c_void) so that they can be converted properly.

Contributing

Contributions to rusty-cheddar are more than welcome.

Bugs

If you find a bug or have a feature request please open an issue. I can't guarantee that I'll fix it but I'll give it a damn good go.

If you find the source code unclear in any way then I consider that a bug. I try to make my source code as clear as possible but I'm not very good at it, so any help in that regard is appreciated.

PRs

I love pull requests they tend to make my job much easier, so if you want to fix a bug or implement a feature yourself then that would be great. If you're confused by anything or need some pointers on how to proceed then feel free to open an issue so that I can help, otherwise these docs are a good place to start.

Tests

I have written a script for comparing two header files, using CppHeaderParser. Unfortunately due to this issue we can't compare structs, so for the time being you'll have to install my fork:

# you'll have to download mercurial and a python (either 2 or 3 should work) first
cd '/path/to/where/you/want/to/store/the/source'
hg clone https://Sean1708@bitbucket.org/Sean1708/cppheaderparser
cd 'cppheaderparser'
pip install ply
pip install .