Implement Vec::pop_if

[igneousflock]

This PR adds Vec::pop_if to the public API, behind the vec_pop_if feature.

impl<T> Vec<T> {
    pub fn pop_if<F>(&mut self, f: F) -> Option<T>
        where F: FnOnce(&mut T) -> bool;
}

Tracking issue: #122741

Open questions

• Should the first unit test be split up?
• I don't see any guidance on ordering of methods in impl blocks, should I move the method elsewhere?

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @joboet (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

• @rustbot author: the review is finished, PR author should check the comments and take action accordingly
• @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

[joboet]

If the predicate modifies the value but returns false, that should be reflected in the vector. Hence this should call f with the value still in the vector, and only then remove it. Also, I'd prefer if this didn't use unsafe, I'd wager that the optimizer is able to deal with a combination of slice::last and Vec::pop just fine.

[igneousflock]

Fair enough, I'll trust your judgement on the optimizer. Switch to last_mut and pop and added a test for an impure predicate.

@rustbot review

[joboet]

Looks great, thank you very much! Could you squash the commits, please?

Then r=me
(this shorthand tells other people with merge rights that they can merge this on my behalf if don't get to it right away)

[igneousflock]

@bors r=joboet

[bors]

@avandesa: 🔑 Insufficient privileges: Not in reviewers

[igneousflock]

Ope, I misunderstood that I think

[clubby789]

@bors r=joboet

[bors]

📌 Commit 07d3806 has been approved by joboet

It is now in the queue for this repository.