{"ast_node_type":"function","tokens":[{"end":78,"kind":"keyword","start":0,"text":"fn"}]}
    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
impl<'tcx> LateLintPass<'tcx> for InvalidFromUtf8 {
        if let ExprKind::Call(path, [arg]) = expr.kind