refactor(eslint/default-case-last): simplify implementation and enhance readability

[antoinezanardi]

Refactor and Standardize: eslint/default-case-last

This PR refactors the implementation of the default-case-last rule to make the codebase more idiomatic Rust, improving readability, maintainability, and alignment with Rust best practices.

In addition, the rule documentation has been standardized and enhanced following the documentation skeleton described in #13389.

Changes included

• Refactored rule logic with clearer naming, early returns, and idiomatic Rust patterns (if let, Option, Iterator, etc.).
• Improved structure for better readability and maintainability.
• Focused on optimization and performances.
• Standardized rule documentation for consistency across the linter rules.

Note

This PR is focused solely on refactoring and documentation; no test behavior is modified.

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[Copilot]

Pull Request Overview

Refactors the default-case-last ESLint rule implementation to use more idiomatic Rust patterns and standardizes the rule documentation following project guidelines.

• Simplified logic using enumerate().find() instead of separate position() calls
• Enhanced documentation with better formatting, examples, and consistent structure
• Moved span calculation to the diagnostic function for better encapsulation

Comments suppressed due to low confidence (1)

crates/oxc_linter/src/rules/eslint/default_case_last.rs:1

• This code example in the documentation uses // comment markers instead of /// for documentation comments. It should use /// to be consistent with other examples in the same documentation block.

use oxc_ast::AstKind;

---

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #13515 will not alter performance

_{Comparing antoinezanardi:refactor/eslint/default-case-last (16f09b2) with main (e4bbbce)}

Summary

✅ 37 untouched benchmarks

[overlookmotel]

I'm late to the party, but... if simplicity is the aim, why not cut out the "is the match the last case?" check entirely, and just don't iterate over the last case in the first place?

if cases.is_empty() {
    return;
}
if let Some(default_clause) = cases[..cases.len() - 1].iter().find(|c| c.test.is_none()) {
    ctx.diagnostic(default_case_last_diagnostic(default_clause.span));
}

[antoinezanardi]

Good catch, do you want me to make another PR to apply your suggestion ?

[overlookmotel]

If you're happy to, then yes please.

By the way, thanks very much for your effort to clean up many linter rules. The linter includes contributions from many many people, some of whom were quite new to Rust. So the quality of the code is mixed, and clean-up is really desirable in many cases. What you're doing is really valuable. Thank you!