Add `Lines::remainder`

[WaffleLapkin]

Proposal

Add Lines::remainder similarly to other remainder methods on split iterators for strings (see tracking issue: rust-lang/rust#77998).

Problem statement

While most iterators that split strings allow to get the remainder, Lines does not.

Motivation, use-cases

It may be beneficial to get the remainder of an iterator, for example to process it differently. A rough sketch:

let lines = s.lines();

while let Some(line) = lines.next() {
    let command = line.parse::<Command>()?;
    // ...
    if command.is_end() {
        process_end(lines.remainder());
        break;
    }
}

Solution sketches

impl<'a> Lines<'a> {
    pub fn remainder(&self) -> Option<&'a str> { /* ... */ }
}

Links and related work

• Tracking issue for similar methods on other iterators: Tracking Issue for remainder methods for str split iterators rust#77998
• Implementation PR: Add str::Lines::remainder rust#107464

What happens now?

This issue is part of the libs-api team API change proposal process. Once this issue is filed the libs-api team will review open proposals in its weekly meeting. You should receive feedback within a week or two.

[pitaj]

Seems like a fitting addition to me

[JohnCSimon]

@WaffleLapkin Ping from triage: Can you post your status on this PR? This has sat idle for a few months.

[WaffleLapkin]

@JohnCSimon it is waiting on review from libs-api (either the ACP or the PR)

[haberman]

Any update? I found myself wanting this method today.

[WaffleLapkin]

@haberman still waiting on T-libs-api. They are having problems with not having enough capacity.

[dtolnay]

This looks good to me, and I have accepted your PR. Thanks!