feat: add is_empty method to check if iterator contains no pairs

[nyurik]

is_empty is now mostly expected from various iterators - to the point that Clippy suggests adding it, and even AI suggests it for pest despite pest code not supporting it. So to make it more ergonomic, I think this helper would ... help :)

Summary by CodeRabbit

• New Features
  • Added is_empty() method for checking whether a collection contains any elements.

[coderabbitai]

Walkthrough

Adds a public is_empty method to the Pairs<'i, R> struct that returns a boolean indicating whether the internal pairs_count is zero. The implementation is a straightforward equality check without additional logic or control-flow modifications.

Changes

Cohort / File(s)	Change Summary
Add is_empty method to Pairs pest/src/iterators/pairs.rs	Added public is_empty(&self) -> bool method to Pairs<'i, R> that checks if pairs_count == 0

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Critical attention needed: The summary indicates the is_empty method appears twice in the impl block, resulting in duplicate declarations. Verify that only one definition exists in the final code, as duplicate method declarations would cause a compilation error.

Poem

🐰 A pair that's empty, bare and light,
Now has a method, clear and bright!
Just check is_empty, swift and clean,
The simplest check we've ever seen! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The PR title "feat: add is_empty method to check if iterator contains no pairs" directly and accurately describes the main change in this pull request. It uses conventional commit format with "feat:" prefix, clearly states what was added (the is_empty method), and explains its purpose (to check if an iterator contains no pairs). The title is concise at 11 words, avoids vague terminology, and provides sufficient specificity for a teammate reviewing the commit history to understand the primary change without needing to inspect the diff.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

pest/src/iterators/pairs.rs (1)

377-380: Consider adding test coverage for is_empty.

While the implementation is straightforward, consider adding a test to verify the method works correctly for both empty and non-empty Pairs. You could extend the existing exact_size_iter_for_pairs test or create a dedicated test.

Example test:

#[test]
fn test_is_empty() {
    let pairs = AbcParser::parse(Rule::a, "abcde").unwrap();
    assert!(!pairs.is_empty());
    
    let mut pairs = AbcParser::parse(Rule::a, "abcde").unwrap();
    pairs.next();
    pairs.next();
    assert!(pairs.is_empty());
}

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between d2dd16c and a8a98ac.

📒 Files selected for processing (1)

• pest/src/iterators/pairs.rs (1 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

pest/src/iterators/pairs.rs (1)

pest/src/stack.rs (1)

• is_empty (61-63)

🔇 Additional comments (1)

pest/src/iterators/pairs.rs (1)

377-380: No duplicate method declaration found—implementation is correct.

The verification confirms only one is_empty declaration exists at line 378. The AI summary's claim of a duplicate was incorrect. The implementation is sound: it correctly checks self.pairs_count == 0 and aligns with the ExactSizeIterator::len() method. No issues remain.