{"ast_node_type":"variable","tokens":[{"end":47,"kind":"keyword","start":0,"text":"let"}]}
            let expr = self.collect_expr(expr);
            let src = self.expander.in_file(AstPtr::new(&expr).wrap_left());
            // Do not use `alloc_pat_from_expr()` here, it will override the entry in `expr_map`.