Function replace_file 

pub fn replace_file(
    directory: &File,
    source_name: &OsStr,
    target_name: &OsStr,
) -> Result<(), ReplaceFileError>

Atomically replace an existing regular file with another regular file in the same directory.

Source contents must already be written. On Windows the implementation reopens and flushes the source through a write-through handle before issuing the NTFS namespace rename through that same handle. On POSIX the caller remains responsible for the containing-directory durability barrier.