{"ast_node_type":"variable","tokens":[{"end":83,"kind":"keyword","start":0,"text":"let"}]}
        let ptr = self as *const ConstArg<'hir> as *const ConstArg<'hir, AmbigArg>;
        // not a `ConstArgKind::Infer` so there is no risk of transmuting a `()` to `AmbigArg`.
        Some(unsafe { &*ptr })