2nd/10_Wiki/Topics/Programming & Language/코드 포매팅 (Code formatting).md

---
id: wiki-2026-0508-코드-포매팅-code-formatting
title: 코드 포매팅 (Code Formatting)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Code Formatting, Auto-formatting, Prettier, Black, gofmt]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [tooling, style, formatter, prettier, ruff, black]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: polyglot
  framework: prettier-ruff-gofmt
---

# 코드 포매팅 (Code Formatting)

## 매 한 줄
> **"매 style debate 의 종결자"**. Code formatting 은 코드의 visual structure (whitespace, indent, line breaks, quote style) 를 deterministic rule 로 enforce 하는 tooling 영역. 2026 현재 매 모든 mainstream language 는 official 또는 de-facto formatter 를 가지며 (Black, Ruff format, Prettier, gofmt, rustfmt, dart format, ktlint), CI 의 commit hook 의 universal 으로 적용. 매 "어떻게 보일지" 의 human discussion 의 X — 매 tool 의 결정.

## 매 핵심

### 매 formatter 의 철학
- **Opinionated** (매 ideal): 매 minimal config — Black, gofmt, Prettier. 매 bikeshedding 의 elimination.
- **Configurable** (매 legacy): 매 ESLint stylistic rules, autopep8 — 매 team config drift 의 risk.
- **Idempotent**: `format(format(x)) == format(x)`. 매 essential property — CI loop safety.
- **AST-based**: 매 token stream 의 parse → reformat. 매 regex 의 X.

### 매 linter vs formatter
- **Formatter**: whitespace, line breaks, quotes (style only). 매 semantics 의 X-change.
- **Linter**: bugs, anti-patterns, unused vars (semantics). 매 ESLint, Ruff check, golangci-lint.
- **2026 trend**: Ruff (Python) 의 both 의 unify — `ruff format` + `ruff check` 의 매 single binary. Biome (JS/TS) 의 same path.

### 매 응용
1. **Pre-commit hook**: `pre-commit` (Python), `lefthook`, `husky` 의 매 staged file 의 format.
2. **CI gate**: `ruff format --check` / `prettier --check` — diff 가 있으면 fail.
3. **Editor on-save**: VS Code `editor.formatOnSave: true` + `defaultFormatter`.
4. **Mass migration**: `git ls-files | xargs ruff format` — 매 single PR 의 entire repo reformat.

## 💻 패턴

### Prettier (JS/TS/JSON/MD/CSS) — 2026 v3
```json
// .prettierrc.json
{
  "semi": false,
  "singleQuote": true,
  "trailingComma": "all",
  "printWidth": 100,
  "tabWidth": 2,
  "plugins": ["prettier-plugin-tailwindcss"]
}
```

```bash
# format all files in repo
npx prettier --write .
# CI check
npx prettier --check .
```

### Ruff format (Python) — 2026 default Python formatter
```toml
# pyproject.toml
[tool.ruff]
line-length = 100
target-version = "py312"

[tool.ruff.format]
quote-style = "double"
indent-style = "space"
docstring-code-format = true  # format code in docstrings
```

```bash
ruff format .         # write
ruff format --check . # CI
ruff check --fix .    # lint + autofix
```

### Black (Python, legacy but stable)
```toml
[tool.black]
line-length = 100
target-version = ["py312"]
skip-string-normalization = false
```

### gofmt / goimports (Go) — bundled with toolchain
```bash
gofmt -w ./...
goimports -w ./...   # also organizes imports
```

```go
// before
package main
import("fmt"
 "os")
func main(){fmt.Println(os.Args)}

// after gofmt
package main

import (
	"fmt"
	"os"
)

func main() {
	fmt.Println(os.Args)
}
```

### rustfmt (Rust)
```toml
# rustfmt.toml
edition = "2024"
max_width = 100
imports_granularity = "Crate"
group_imports = "StdExternalCrate"
```

```bash
cargo fmt
cargo fmt -- --check  # CI
```

### EditorConfig (cross-tool baseline)
```ini
# .editorconfig — every editor respects this
root = true

[*]
charset = utf-8
end_of_line = lf
insert_final_newline = true
trim_trailing_whitespace = true
indent_style = space

[*.{js,ts,tsx,json}]
indent_size = 2

[*.py]
indent_size = 4

[Makefile]
indent_style = tab
```

### Pre-commit hook (universal)
```yaml
# .pre-commit-config.yaml
repos:
  - repo: https://github.com/astral-sh/ruff-pre-commit
    rev: v0.6.0
    hooks:
      - id: ruff-format
      - id: ruff
        args: [--fix]
  - repo: https://github.com/pre-commit/mirrors-prettier
    rev: v4.0.0
    hooks:
      - id: prettier
        types_or: [javascript, typescript, json, markdown]
```

### CI gate (GitHub Actions)
```yaml
- name: Check formatting
  run: |
    ruff format --check .
    ruff check .
    npx prettier --check .
```

### Mass-format ignore (avoid blame churn)
```
# .git-blame-ignore-revs
# Ruff format mass-apply 2026-04-15
abc123def456...
```
```bash
git config blame.ignoreRevsFile .git-blame-ignore-revs
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Python 신규 프로젝트 | Ruff format (Black-compatible, 100x faster) |
| Python legacy | Black 유지 — Ruff 의 drop-in 의 가능 |
| JS/TS | Prettier 또는 Biome (faster, Rust-based) |
| Go | gofmt (no choice, no config) |
| Rust | rustfmt |
| 매 polyglot monorepo | dprint 또는 Trunk |
| Team debate 중 | Opinionated formatter 의 즉시 채택 — 매 discussion close |

**기본값**: Ruff (Python), Prettier 또는 Biome (web), gofmt (Go), rustfmt (Rust). 매 pre-commit + CI check.

## 🔗 Graph
- 부모: [[Code Quality]] · [[Developer Experience]]
- 변형: [[Linter]] · [[Static Analysis]]
- 응용: [[153_pre-commit과_품질_게이트|Pre-commit Hooks]]
- Adjacent: [[Prettier]]

## 🤖 LLM 활용
**언제**: Generated code 의 file write 후 항상 `ruff format` / `prettier --write` 의 run — LLM output 의 indent inconsistency 의 normalize. PR diff 의 minimize.
**언제 X**: Format-only PR 의 logic change 와 mix 의 X — separate commit / PR 로 분리. Reviewer 의 noise 의 reduction.

## ❌ 안티패턴
- **Custom rules everywhere**: 매 team-specific style 의 invention. 매 onboarding cost 의 increase. 매 Black/Prettier default 의 accept.
- **Format on commit only**: Editor save 의 X-format 의 경우 매 every commit 의 noise. Editor integration 의 essential.
- **Format + logic 의 mixed PR**: Review impossible. 매 separate PR.
- **No CI check**: Pre-commit 의 bypass 의 가능 (`-n`). 매 CI 의 source of truth.
- **`tabWidth` debate**: 매 EditorConfig 의 fix — once and forget.

## 🧪 검증 / 중복
- Verified (Prettier docs 2026, Ruff docs 0.6+, Go style guide).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — formatters (Ruff, Prettier, gofmt, rustfmt) + CI/pre-commit patterns |