error[E0596]: cannot borrow data in an index of `std::collections::HashMap>` as mutable --> $DIR/issue-41726.rs:5:9 | LL | things[src.as_str()].sort(); | ^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable | = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap>` error: aborting due to previous error For more information about this error, try `rustc --explain E0596`.