rust-clippy/tests/ui/map_flatten.stderr

error: called `map(..).flatten()` on an `Iterator`. This is more succinctly expressed by calling `.flat_map(..)`
  --> $DIR/map_flatten.rs:5:21
   |
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: aborting due to previous error