{"ast_node_type":"variable","tokens":[{"end":57,"kind":"keyword","start":0,"text":"if"}]}
        if let hir::ExprKind::Call(f, [arg]) = &expr.kind
    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
            && let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind()