Function rustc_parse::new_parser_from_source_file

pub(crate) fn new_parser_from_source_file(
    psess: &ParseSess,
    source_file: Lrc<SourceFile>,
) -> Result<Parser<'_>, Vec<Diag<'_>>>

Given a session and a source_file, return a parser. Returns any buffered errors from lexing the initial token stream.