/// A macro for [`CStr`] literals.

///

/// This can make passing string literals to rustix APIs more efficient, since

/// most underlying system calls with string arguments expect NUL-terminated

/// strings, and passing strings to rustix as `CStr`s means that rustix doesn't

/// need to copy them into a separate buffer to NUL-terminate them.

///

/// In Rust ≥ 1.77, users can use [C-string literals] instead of this macro.

///

/// [`CStr`]: crate::ffi::CStr

/// [C-string literals]: https://blog.rust-lang.org/2024/03/21/Rust-1.77.0.html#c-string-literals

///

/// # Examples

///

/// ```

/// # #[cfg(feature = "fs")]

/// # fn main() -> rustix::io::Result<()> {

/// use rustix::cstr;

/// use rustix::fs::{statat, AtFlags, CWD};

///

/// let metadata = statat(CWD, cstr!("Cargo.toml"), AtFlags::empty())?;

/// # Ok(())

/// # }

/// # #[cfg(not(feature = "fs"))]

/// # fn main() {}

/// ```

#[allow(unused_macros)]

#[macro_export]

macro_rules! cstr {

    ($str:literal) => {{

        // Check for NUL manually, to ensure safety.

        //

        // In release builds, with strings that don't contain NULs, this

        // constant-folds away.

        //

        // We don't use std's `CStr::from_bytes_with_nul`; as of this writing,

        // that function isn't defined as `#[inline]` in std and doesn't

        // constant-fold away.

        assert!(

            !$str.bytes().any(|b| b == b'\0'),

            "cstr argument contains embedded NUL bytes",

        );

        #[allow(unsafe_code, unused_unsafe)]

        {

            // Now that we know the string doesn't have embedded NULs, we can

            // call `from_bytes_with_nul_unchecked`, which as of this writing

            // is defined as `#[inline]` and completely optimizes away.

            //

            // SAFETY: We have manually checked that the string does not

            // contain embedded NULs above, and we append or own NUL terminator

            // here.

            unsafe {

                $crate::ffi::CStr::from_bytes_with_nul_unchecked(concat!($str, "\0").as_bytes())

            }

        }

    }};

}

#[cfg(test)]

mod tests {

    #[allow(unused_imports)]

    use super::*;

    #[test]

    fn test_cstr() {

        use crate::ffi::CString;

        use alloc::borrow::ToOwned as _;

        assert_eq!(cstr!(""), &*CString::new("").unwrap());

        assert_eq!(cstr!("").to_owned(), CString::new("").unwrap());

        assert_eq!(cstr!("hello"), &*CString::new("hello").unwrap());

        assert_eq!(cstr!("hello").to_owned(), CString::new("hello").unwrap());

    }

    #[test]

    #[should_panic]

    fn test_invalid_cstr() {

        let _ = cstr!("hello\0world");

    }

    #[test]

    #[should_panic]

    fn test_invalid_empty_cstr() {

        let _ = cstr!("\0");

    }

}