Enhancements for `manual_flatten` · rust-lang/rust-clippy#6676

2021-02-05T01:40:42.000Z

Enhancements for `manual_flatten` 1) `for_each` Before: ```rust iter.for_each(|o| { if let Some(x) = o { //.. } }) ``` After ```rust iter.flatten().for_each(|o| //..) ``` 2) nested loops Before: ```rust for x in vec![vec![1]] { for y in x { //.. x is not used again } } ``` After: ```rust for x in vec![vec![1]].into_iter().flatten() { // .. } ```

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C-enhancementL-stylegood first issue

Description

Enhancements for manual_flatten

for_each

Before:

iter.for_each(|o| {
    if let Some(x) = o { //.. }
})

After

iter.flatten().for_each(|o| //..)

nested loops

Before:

for x in vec![vec![1]] {
    for y in x {
        //..  x is not used again
    }
}

After:

for x in vec![vec![1]].into_iter().flatten() {
    // ..
}

Contributor guide

Tech stack: rust
Domain: tooling
Issue type: feature
Difficulty: 2
Estimated time: 1-3 hours
Activity status: blocked
Clarity: clear
Prerequisites: Basic RustClippy lint basicsIterator concepts
Newbie friendliness: 50
Research direction: The issue requests enhancements to the `manual flatten` lint in Clippy. The contributor should locate the existing implementation in the `clippy lints/src` directory, likely in a file named `manual flatten.rs` or similar. Two specific patterns need to be added: one for `for each` with `if let Some` and one for nested loops where the outer variable is unused. Since the issue has an assignee (ayamdobhal), it is recommended to check the current status and coordinate if possible. The existing test cases for `manual flatten` should also be extended.