VaList struct might not have foreign-function safe representation

[pnkfelix]

Currently when I do:

extern crate va_list;

extern {
    fn foo(args: va_list::VaList);
}

I get the following message from rustc:

% cargo build
   Compiling ffi-play v0.1.0 (file:///Users/fklock/Dev/Rust/ffi-play)
src/lib.rs:4:18: 4:33 warning: found struct without foreign-function-safe representation annotation in foreign module, consider adding a #[repr(C)] attribute to the type, #[warn(improper_ctypes)] on by default
src/lib.rs:4     fn foo(args: va_list::VaList);
                              ^~~~~~~~~~~~~~~

At first I took this as a sign that this crate merely needs to add #[repr(C)] attribute(s) in appropriate places.

However, eddyb on IRC pointed out that this might not suffice: https://botbot.me/mozilla/rust-internals/2016-02-16/?msg=60150124&page=4

In any case, it seems like the compiler warning is going to (perhaps rightfully) scare off users of this crate. So you may want to address it.

[richard-uk1]

Working with va_args is always going to be very unsafe. It relies on the particular implementation of the va_* macros. I've been through the implementation and I'm pretty sure this warning is a false-positive.

[thepowersgang]

Fixed with dac37e7 (hopefully for all architectures)