error: called `map(..).flatten()` on an `Iterator`. This is more succinctly expressed by calling `.flat_map(..)` --> $DIR/map_flatten.rs:8:21 | LL | let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `flat_map` instead: `vec![5_i8; 6].into_iter().flat_map(|x| 0..x)` | = note: `-D clippy::map-flatten` implied by `-D warnings` error: called `map(..).flatten()` on an `Option`. This is more succinctly expressed by calling `.and_then(..)` --> $DIR/map_flatten.rs:9:24 | LL | let _: Option<_> = (Some(Some(1))).map(|x| x).flatten(); | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `and_then` instead: `(Some(Some(1))).and_then(|x| x)` error: aborting due to 2 previous errors