Function rustc_ap_rustc_parse::new_parser_from_file

pub fn new_parser_from_file<'a>(
    sess: &'a ParseSess, 
    path: &Path, 
    sp: Option<Span>
) -> Parser<'a>

Creates a new parser, handling errors as appropriate if the file doesn't exist. If a span is given, that is used on an error as the as the source of the problem.