{"ast_node_type":"variable","tokens":[{"end":60,"kind":"keyword","start":0,"text":"let"}]}
            let id = self.store.pats.alloc(Pat::Expr(expr));
            // Do not use `alloc_pat_from_expr()` here, it will override the entry in `expr_map`.
            self.source_map.pat_map_back.insert(id, src);