{"ast_node_type":"impl","tokens":[{"end":93,"kind":"keyword","start":0,"text":"walk_flat_map:"}]}
        walk_flat_map: impl FnOnce(Self, &mut InvocationCollector<'_, '_>) -> Self::OutputTy,
        collector: &mut InvocationCollector<'_, '_>,
    ) -> Result<Self::OutputTy, Self> {