Variadic Functions in C with Ternery Operators Return Error with Unified Header Files

[9p4]

Zig Version

0.13.0

Steps to Reproduce and Observed Behavior

Minimal reproduction:

// In file a.h
#include <stdio.h>

void a(int a) {
    printf("a %s\n", (a) ? "a" : "bb");
}

// In file test.zig
const a = @cImport({
    @cInclude("a.h");
});

pub fn main() void {
    a.a(1);
}

Build with zig build-exe test.zig --library c -I.

Compiler error:

/home/user/.cache/zig/o/0200dc12bc56a44b101a174bbd0f10db/cimport.zig:297:26: error: cannot pass '[:0]const u8' to variadic function
    _ = printf("a %s\n", if (a_1 != 0) "a" else "bb");
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/user/.cache/zig/o/0200dc12bc56a44b101a174bbd0f10db/cimport.zig:297:26: note: slices have no guaranteed in-memory representation
referenced by:
    main: test.zig:6:6
    callMain: /nix/store/vm8x0fdp3gn99adhig5g0z9ri40hrq3w-zig-0.13.0/lib/zig/std/start.zig:514:17
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

Expected Behavior

Interestingly, this issue doesn't happen when the header is separated from the functions themselves.

// In file a.h
#include <stdio.h>

void a(int);

// In file a.c
#include "a.h"

void a(int a) {
    printf("a %s\n", (a) ? "a" : "bb");
}

Build with zig build-exe test.zig a.c --library c -I., no error