<!-- Hi there! Whether you've come to make a suggestion for a new lint, an improvement to an existing lint or to report a bug or a false positive in Clippy, you've come to the right place. For bug reports and false positives, please include the output of `cargo clippy -V` in the report. Thank you for using Clippy! Write your comment below this line: --> Clippy should suggest using `.flatten()` instead of `.flat_map(|x| x)`.