{"ast_node_type":"impl","tokens":[{"end":77,"kind":"keyword","start":0,"text":"//"}]}
        // FIXME: Once we remove support for the old impl we can remove this.
        // assertions against dropping an `InferCtxt` without taking opaques.
        // FIXME: Could we make `build_with_canonical` into `enter_with_canonical` and call this at the end?