⚡ Bolt: [성능 최적화] O(n^2) 디렉토리 처리 및 문자열 연결 병목 현상 제거

[seonghobae]

💡 What:

• process_ignore_file가 반환하는 파일 제외 목록의 데이터 구조를 List에서 Set으로 변경했습니다.
• 디렉토리 파일을 루프할 때 발생하는 문자열의 반복적인 결합(+=) 대신 StringBuilder를 도입했습니다.
• 성능 최적화의 의도를 명확하게 보여주는 인라인 주석을 코드에 추가했습니다.
• 코드베이스의 동작을 증명하는 JUnit 단위 테스트를 추가하고 Jacoco를 이용한 100% 테스트 커버리지를 구현했습니다.

🎯 Why:
디렉토리 목록을 생성할 때마다 하위의 모든 파일들을 순회(n번)하고, 이 과정 내에서 무시할 파일 목록을 조회하거나 문자열을 덧붙이는 동작을 합니다. List 내 요소의 존재 여부를 묻는 !in 연산은 요소의 개수만큼 확인하므로 O(n)의 복잡도를 가지며 전체적으로는 O(n^2)의 비용을 발생시킵니다. 마찬가지로, 문자열에 +=를 수행하면 매번 새로운 객체를 재할당하므로 역시 O(n^2)의 메모리 비용을 발생시키는 심각한 성능 안티패턴이었습니다.

📊 Impact:
디렉토리 내 파일 수가 많을수록 제곱 단위로 증가하던 탐색 시간과 메모리 사용량이 O(1) 조회와 단일 메모리 버퍼 (StringBuilder)를 통해 선형적(Linear)으로 감소하게 됩니다.

🔬 Measurement:
다음 Gradle 명령어를 통해 단위 테스트의 통과 여부 및 100% 분기/라인 커버리지를 검증할 수 있습니다.
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64 && ./gradlew build jacocoTestReport jacocoTestCoverageVerification

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PR created automatically by Jules for task 4159131252985411441 started by @seonghobae

[google-labs-jules]

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[Copilot]

Pull request overview

This PR focuses on improving performance of directory traversal and HTML index generation by removing O(n²) patterns in ignore lookups and string construction, and adds unit tests plus Jacoco configuration to validate behavior and enforce coverage.

Changes:

• Changed ignore-list handling to use a Set for faster membership checks.
• Replaced looped string concatenation with StringBuilder when building directory listing HTML.
• Added JUnit tests and introduced Jacoco reporting/coverage verification configuration.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/main/kotlin/html4tree/main.kt	Switches ignore results to Set and uses StringBuilder when rendering directory entries.
src/test/kotlin/html4tree/MainTest.kt	Adds tests covering escaping/encoding, ignore processing, directory index generation, CLI behaviors, and help().
src/test/kotlin/html4tree/LinkedListTest.kt	Adds tests for LinkedList/entry data classes and push/pull behavior.
build.gradle	Adds Jacoco plugin and coverage report/verification tasks.
.jules/bolt.md	Documents the performance learnings motivating the optimization.

Comments suppressed due to low confidence (1)

src/main/kotlin/html4tree/main.kt:77

• File.list() can return null (e.g., unreadable directory / I/O error). Calling .forEach on it can throw at runtime, which would break ignore processing. Treat a null listing as empty.

       curr_dir.list().forEach {
           val current = it
           ignored_regexes.forEach { regex ->
              if(regex.matches(current)){
                 files_to_exclude.add(current)

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[seonghobae]

Closing as superseded by already-merged performance fixes (#20/#21). Current master already uses a Set for ignore exclusions and StringBuilder for generated listing rows, while also preserving newer safe URL encoding, invalid-regex handling, symlink protections, and accessibility output.

[google-labs-jules]

Closing as superseded by already-merged performance fixes (#20/#21). Current master already uses a Set for ignore exclusions and StringBuilder for generated listing rows, while also preserving newer safe URL encoding, invalid-regex handling, symlink protections, and accessibility output.

Understood. Acknowledging that this work is superseded by already-merged PRs and stopping work on this task.