error[E0433]: failed to resolve: use of undeclared type `HashMap` --> $DIR/issue-31997-1.rs:20:19 | LL | let mut map = HashMap::new(); | ^^^^^^^ use of undeclared type `HashMap` | help: consider importing this struct | LL + use std::collections::HashMap; | error: aborting due to previous error For more information about this error, try `rustc --explain E0433`.