this module through its public re-export | 10 + use crate::hosting; | warning: unused import: `crate::front_of_house::hosting` --> src/lib.rs:7:5 | 7 | use crate::front_of_house::hosting; Compiling rand v0.8.5 Compiling add_one v0.1.0 (file:///projects/add/add_one) warning: unused import: `rand` --> add_one/src/lib.rs:1:5 | 1 | use rand; | ^^^^ | = note: `#[warn(unused_imports)]` build --snip-- Compiling adder v0.1.0 (file:///projects/add/adder) error[E0432]: unresolved import `rand` --> adder/src/main.rs:2:5 | 2 | use rand; | ^^^^ no external crate `rand` 为了修复这个错误，修改顶级