Function diff_file 

pub fn diff_file(
    lhs_display_path: &str,
    rhs_display_path: &str,
    lhs_path: &Path,
    rhs_path: &Path,
    display_options: &DisplayOptions,
    missing_as_empty: bool,
    graph_limit: usize,
    byte_limit: usize,
    language_override: Option<Language>,
) -> DiffResult

Print a diff between two files.