{"ast_node_type":"other","tokens":[{"end":77,"kind":"keyword","start":0,"text":"//"}]}
    // FIXME(eddyb) build a better abstraction for permutations, if possible.
    /// See also `FieldsShape::Arbitrary::memory_index` for more details.
    pub fn invert_bijective_mapping(&self) -> IndexVec<J, I> {