Add a check for some followed by filter

[qmwrygdxpzc]

Add a check for some followed by filter.

The program will suggest using the then_some method.

changelog: [filter_some]: https://rust-lang.github.io/rust-clippy/master/index.html#filter_some

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[github-actions]

No changes for edd2d3b

[samueltardieu]

Thanks for your contribution. However, the lint cannot be considered for merging as-is:

• It should include autofixes suggestions when possible.
• It should cover more complex cases.

For example, with the following code

fn with_side_effect(x: u32) -> u32 {
    println!("In `with_side_effect()`");
    x * 10 + 30
}

fn f(x: u32) -> Option<u32> {
    Some(with_side_effect(x)).filter(|&x| x > 40)
}

the lint suggests using then_some() inside f(). However, I don't see what would be the replacement code here.

You should include tests for the most complicated situations you can think of, as the lint should not fail, don't just cover the simplest case where it is obvious it will work. For example, what is part of the expression comes from a macro? Also, bool::then_some() has been introduced in Rust 1.62.0, so the MSRV must be checked as well.

Hope this review will help you go forward.

View changes since this review

[qmwrygdxpzc]

In the example with the 2 functions, what should the linter do?

[samueltardieu]

In the example with the 2 functions, what should the linter do?

Probably nothing.

[qmwrygdxpzc]

It has been about 2 weeks. Can someone take a look?