{"ast_node_type":"function","tokens":[{"end":92,"kind":"keyword","start":0,"text":"fn"}]}
    fn pattern_cause(&self, ti: &TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
        // If origin_expr exists, then expected represents the type of origin_expr.