Function read_loop 

pub fn read_loop(fd: i32, buf: &mut [u8]) -> Result<usize>

Port of ssize_t read_loop(int fd, char *buf, size_t len) from Src/utils.c:2923.

C body (c:2923-2945):

while (1) {
    ssize_t ret = read(fd, buf, len);
    if (ret == len) break;
    if (ret <= 0) {
        if (ret < 0) {
            if (errno == EINTR) continue;          // c:2933
            if (fd != SHTTY)                       // c:2935
                zwarn("read failed: %e", errno);   // c:2936
        }
        return ret;
    }
    buf += ret; len -= ret;
}

The previous Rust port omitted the zwarn("read failed: %e", errno) emission at c:2935-2936. That’s a real diagnostic divergence: any non-SHTTY read failure in zsh emits a stderr message; the Rust port silently propagated the io::Error to the caller, which in most call sites was discarded (let _ = read_loop(...)). Users debugging an interrupted file read (e.g. < /broken/fd) would see no error message at all. WARNING: param names don’t match C — Rust=(fd, buf) vs C=(fd, buf, len)