{"ast_node_type":"other","tokens":[{"end":91,"kind":"keyword","start":0,"text":"//"}]}
        // by using a `Cell` here. We only ever write into it inside of `match_assumption`.
        // in `probe` even if the candidate does not apply before we get there. We handle this
        let source = Cell::new(CandidateSource::ParamEnv(ParamEnvSource::Global));