closure-ffi 5.1.2

FFI utility for creating bare function pointers that invoke a closure
Documentation 
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#![cfg(feature = "c_variadic")]
#![feature(c_variadic)]

use std::ffi::{CStr, VaList};

use closure_ffi::BareFnMut;

mod slab_alloc;
use slab_alloc::SLAB;

unsafe extern "C" {
    fn vsprintf(buf: *mut u8, fmt: *const u8, va: VaList<'_>);
}

#[test]
fn test_variadic() {
    let mut buf = [0u8; 128];
    let fmt = b"dec = %d, hex = %llX, chr = %c, pi = %.2f\0";

    let bare_fn = BareFnMut::new_variadic_in(
        |va: VaList| unsafe {
            vsprintf(buf.as_mut_ptr(), fmt.as_ptr(), va);
        },
        &SLAB,
    );

    unsafe { bare_fn.bare()(42, 0xDEADBEEF123u64, '?', core::f64::consts::PI) }
    drop(bare_fn);

    let formatted = CStr::from_bytes_until_nul(&buf).unwrap().to_string_lossy();
    assert_eq!(formatted, "dec = 42, hex = DEADBEEF123, chr = ?, pi = 3.14");
}