error[E0499]: cannot borrow `v` as mutable more than once at a time --> $DIR/two-phase-sneaky.rs:10:9 | LL | v[0].push_str({ | - -------- first borrow later used by call | | | first mutable borrow occurs here LL | LL | v.push(format!("foo")); | ^ second mutable borrow occurs here error: aborting due to previous error For more information about this error, try `rustc --explain E0499`.