1 error[E0596]: cannot borrow data in an index of `Container` as mutable
2 --> $DIR/issue-44405.rs:21:5
4 LL | container[&mut val].test();
5 | ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
7 = help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `Container`
9 error: aborting due to previous error
11 For more information about this error, try `rustc --explain E0596`.