error[E0596]: cannot borrow `b` as mutable, as it is not declared as mutable --> $DIR/mut-borrow-of-mut-ref.rs:4:10 | LL | pub fn f(b: &mut i32) { | ^ not mutable ... LL | h(&mut b); | ------ cannot borrow as mutable ... LL | g(&mut &mut b); | ------ cannot borrow as mutable | note: the binding is already a mutable borrow --> $DIR/mut-borrow-of-mut-ref.rs:4:13 | LL | pub fn f(b: &mut i32) { | ^^^^^^^^ help: try removing `&mut` here | LL - h(&mut b); LL + h(b); | help: try removing `&mut` here | LL - g(&mut &mut b); LL + g(&mut b); | error[E0596]: cannot borrow `b` as mutable, as it is not declared as mutable --> $DIR/mut-borrow-of-mut-ref.rs:17:12 | LL | h(&mut &mut b); | ^^^^^^ cannot borrow as mutable | note: the binding is already a mutable borrow --> $DIR/mut-borrow-of-mut-ref.rs:16:13 | LL | pub fn g(b: &mut i32) { | ^^^^^^^^ help: try removing `&mut` here | LL - h(&mut &mut b); LL + h(&mut b); | error[E0596]: cannot borrow `f` as mutable, as it is not declared as mutable --> $DIR/mut-borrow-of-mut-ref.rs:34:5 | LL | f.bar(); | ^ cannot borrow as mutable | help: consider making the binding mutable | LL | pub fn baz(mut f: &mut String) { | +++ error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0596`.