1 error[E0502]: cannot borrow `*map` as mutable because it is also borrowed as immutable
2 --> $DIR/get_default.rs:32:17
4 LL | fn err(map: &mut Map) -> &String {
5 | - let's call the lifetime of this reference `'1`
8 | --- immutable borrow occurs here
10 LL | map.set(String::new()); // Both AST and MIR error here
11 | ^^^ mutable borrow occurs here
14 | - returning this value requires that `*map` is borrowed for `'1`
16 error: aborting due to previous error
18 For more information about this error, try `rustc --explain E0502`.