refactor: use Set instead of Map in no-duplicate-keys

[lumirlumir]

Prerequisites checklist

• I have read the contributing guidelines.

AI acknowledgment

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What is the purpose of this pull request?

A similar refactor to the one in eslint/css#513.

What changes did you make? (Give an overview)

While reviewing the no-duplicate-keys code, I found that there was no need to use a Map, so I replaced it with a Set.

Related Issues

Ref: eslint/css#513

Is there anything you'd like reviewers to focus on?

N/A

Summary by CodeRabbit

• Refactor
  • Simplified internal duplicate-key tracking while preserving normalized-key duplicate detection behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 780bfcd and a263abd.

📒 Files selected for processing (1)

• src/rules/no-duplicate-keys.js

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📝 Walkthrough

Walkthrough

The duplicate-key rule now uses per-object Set<string> instances to track normalized keys. It removes the unused MemberNode type import and no longer stores the first member node.

Changes

Duplicate Key Tracking

Layer / File(s)	Summary
Set-based duplicate tracking src/rules/no-duplicate-keys.js	The rule replaces per-object maps with string sets, records keys with Set.add, and removes the unused MemberNode type import.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to a263a

This refactor replaces presence-only Map tracking with Sets while preserving duplicate-key detection behavior. No current merge-blocking risk is identified.

Suggested reviewers: pixel998

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: replacing the Map with a Set in no-duplicate-keys.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/use-set-instead-of-map

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[mdjermanovic]

LGTM, thanks!