{"ast_node_type":"impl","tokens":[{"end":74,"kind":"keyword","start":0,"text":"//"}]}
        // and a `(): Trait<?0>` goal we recurse into the impl and look at
        // that candidate. This means that for `impl<F: FnOnce(u32)> Trait<F> for () {}`
        // the nested `?0: FnOnce(u32)` goal.