Add lint for calling `VecDeque::swap` as it might panic

What it does

Triggers on use of possibly-panicking function VecDeque::swap when index is out of bounds, similar to existing lint clippy::indexing_slicing.

Categories (optional)

• Kind: restriction

Recommended code would not panic, swap would. For users trying to prevent all (or all non-std) panics, this would be useful.

For example:

• Do not use .swap, instead use let (a, b) = get_mut(0)?, get_mut(1)?; std::mem::swap(&a, &b);

Drawbacks

None.

Example

#![warn(clippy::all, clippy::pedantic, clippy::nursery, clippy::restriction)]
#![allow(clippy::missing_docs_in_private_items, clippy::blanket_clippy_restriction_lints)]
use std::collections::VecDeque;

fn main() {
    let mut c: VecDeque<u8> = VecDeque::new();
    c.push_back(0);
    c.push_back(1);
    
    let _ = c[0]; // clippy::indexing_slicing correctly detects possible panic

    c.swap(0, 1); // Could cause panic; clippy ignores this line
    // c.swap(1, 2); // Example swap panic
}

Could be written as:

// ...
  // Honestly I don't know the right way to do this. I would expect something like this
  // But you can't borrow c mutably more than once
  let (a, b) = (c.get_mut(0)?, c.get_mut(1)?);
  std::mem::swap(&a, &b);
// ...

Start by reviewing the existing clippy::indexing_slicing lint and how it handles potentially panicking operations. Use the VecDeque::swap examples in this issue to define the expected cases, and consider the suggested get_mut approach when checking the intended non-panicking alternative. Done means the lint identifies potentially out-of-bounds VecDeque::swap calls without incorrectly flagging safe usage.