clippy::manual_filter_map: `filter(..).map(..)` can be simplified as `filter_map(..)`

What you see

warning: `filter(..).map(..)` can be simplified as `filter_map(..)`
 --> main.rs:4:6
  |
4 |       .filter(|n| n.checked_add(1).is_some())
  |  ______^
5 | |     .map(|n| n.checked_add(1).unwrap());
  | |_______________________________________^ help: try: `filter_map(|n| n.checked_add(1))`
  |
note: the suggestion might change the behavior of the program when merging `filter` and `map`, because this expression potentially contains side effects and will only execute once
 --> main.rs:4:17
  |
4 |     .filter(|n| n.checked_add(1).is_some())
  |                 ^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/stable/index.html#manual_filter_map
  = note: `#[warn(clippy::manual_filter_map)]` on by default

Real output of Clippy 0.1.99 (Rust 1.99) on the example below. Names and line numbers in yours will differ.

Does it matter?

Redundant code in the filter and map operations is poor style and less performant.

Code that does something simple in a complicated way. Warns by default.

How to fix it

Clippy can fix this one for you: run cargo clippy --fix (add --allow-dirty if you have uncommitted changes). Review the diff before you commit.

Flagged

(0_i32..10)
    .filter(|n| n.checked_add(1).is_some())
    .map(|n| n.checked_add(1).unwrap());

Write this instead

(0_i32..10).filter_map(|n| n.checked_add(1));

Turn it off, or on

Allow it where it does not fit your code, as narrowly as you can:

#[allow(clippy::manual_filter_map)]
fn my_function() { /* ... */ }

[lints.clippy]
manual_filter_map = "allow"

cargo clippy -- -A clippy::manual-filter-map

The [lints] table needs Rust 1.74 or newer. In a workspace, put it under [workspace.lints.clippy] and add [lints] workspace = true to each member.