perf: optimize duplicate handler filtering

[OskarLebuda]

🔗 Linked issue

n/a

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

The current implementation uses findIndex inside filter, which scans the entire array for each handler - resulting in O(n2) complexity.

Replaced with a Set-based approach for O(1) lookups instead of repeatedly scanning the array. Behavior stays the same - keeps first occurrence, removes duplicates.

For large applications with many routes, this should provide noticeable performance improvement during startup.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[vercel]

@OskarLebuda is attempting to deploy a commit to the Nitro Team on Vercel.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The deduplication logic in scanHandlers is updated to use key-based deduplication with a Set instead of index-based deduplication. A composite key combining route, method, and env is created for each handler, ensuring only the first occurrence of each unique key is included in nitro.scannedHandlers.

Changes

Cohort / File(s)	Summary
Deduplication refactor src/scan.ts	Replaced index-based deduplication with Set-based key deduplication using a composite key (route, method, env) to prevent duplicate handler emissions.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'perf: optimize duplicate handler filtering' follows conventional commits format with a 'perf' type prefix and describes the optimization change accurately.
Description check	✅ Passed	The description clearly explains the performance optimization (O(n²) to O(1) approach), the problem it solves, and maintains the same behavior while improving startup performance.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

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

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commit: 747ee21

[pi0]

thnx!