⚡ Bolt: 문자열 병합 최적화 (O(N^2) -> O(N))

[seonghobae]

💡 무엇을: index_middle 함수 내부에서 디렉토리 파일들을 반복문으로 돌며 HTML 문자열을 병합할 때, + 연산자 대신 StringBuilder를 사용하도록 최적화했습니다. 테스트 커버리지는 JaCoCo 플러그인을 추가하고 테스트 케이스를 강화하여 100%를 달성했습니다.
🎯 왜: Kotlin에서 반복문 내 문자열 병합(l += ...)은 문자열의 불변성 때문에 매 반복마다 새로운 문자열 객체를 할당하여 O(N^2)의 성능 저하를 일으키기 때문입니다.
📊 영향력: 파일이 많은 디렉토리에서 index.html을 생성할 때 반복적인 메모리 재할당과 가비지 컬렉션(GC) 압박을 크게 줄여 성능이 대폭 향상됩니다 (성능복잡도가 O(N^2)에서 O(N)으로 개선됨).
🔬 측정 방법: 파일이 많은 디렉토리를 대상으로 ./gradlew run --args="large_dir"를 실행해보면 최적화 전후의 생성 속도 차이를 확인할 수 있으며, 기존 로직이 정상 작동함은 ./gradlew test jacocoTestReport를 통해 100% 테스트 커버리지로 검증했습니다.

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PR created automatically by Jules for task 13820306230969905600 started by @seonghobae

[google-labs-jules]

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[Copilot]

Pull request overview

This PR improves html4tree’s directory index generation performance by optimizing HTML list-item string construction inside process_dir, and adds automated testing/coverage tooling to validate behavior and report coverage.

Changes:

• Replaced per-iteration string concatenation in index_middle with StringBuilder-based accumulation.
• Added a new Kotlin/JUnit test suite to cover CLI, directory processing, and utility behavior.
• Enabled JaCoCo reporting in the Gradle build and documented the performance lesson in .jules/bolt.md.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/main/kotlin/html4tree/main.kt	Switches HTML concatenation logic in index_middle to a StringBuilder approach.
src/test/kotlin/html4tree/Html4treeTest.kt	Adds tests covering CLI entrypoints and directory/index generation behaviors.
build.gradle	Applies JaCoCo plugin and configures the jacocoTestReport reports.
.jules/bolt.md	Documents the “String concatenation in loops” performance learning/action.

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[seonghobae]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved and pushed in commit c52452d. The branch now includes the latest base changes with conflicts fixed in src/main/kotlin/html4tree/main.kt, and tests are passing.

[seonghobae]

Closing as superseded by already-merged StringBuilder optimization (#21). Current master already uses StringBuilder for directory listing rendering; this branch is stale and would reintroduce older generator/test assumptions if merged directly.

[google-labs-jules]

Closing as superseded by already-merged StringBuilder optimization (#21). Current master already uses StringBuilder for directory listing rendering; this branch is stale and would reintroduce older generator/test assumptions if merged directly.

Understood. Acknowledging that this work is now obsolete and stopping work on this task.