rust/compiler/rustc_data_structures/src/const_cstr.rs

/// This macro creates a zero-overhead &CStr by adding a NUL terminator to
/// the string literal passed into it at compile-time. Use it like:
///
/// ```
///     let some_const_cstr = const_cstr!("abc");
/// ```
///
/// The above is roughly equivalent to:
///
/// ```
///     let some_const_cstr = CStr::from_bytes_with_nul(b"abc\0").unwrap()
/// ```
///
/// Note that macro only checks the string literal for internal NULs if
/// debug-assertions are enabled in order to avoid runtime overhead in release
/// builds.
#[macro_export]
macro_rules! const_cstr {
    ($s:expr) => {{
        use std::ffi::CStr;

        let str_plus_nul = concat!($s, "\0");

        if cfg!(debug_assertions) {
            CStr::from_bytes_with_nul(str_plus_nul.as_bytes()).unwrap()
        } else {
            unsafe { CStr::from_bytes_with_nul_unchecked(str_plus_nul.as_bytes()) }
        }
    }};
}