{"ast_node_type":"variable","tokens":[{"end":73,"kind":"keyword","start":0,"text":"let"}]}
        let src = node.map(AstPtr::new).map(AstPtr::upcast::<ast::Expr>);
    ) -> Option<(ExprId, &[Vec<(syntax::TextRange, usize)>])> {
        let expr = self.expr_map.get(&src)?.as_expr()?;