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AST 代码分析

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用 ast-grep 做基于 AST 的代码模式分析,查找安全、性能与结构问题。

---
name: ast-code-analysis-superpower
description: 使用 ast-grep 进行基于 AST 的代码模式分析,用于安全、性能和结构问题。适用于以下情况:(1) 审查代码以查找安全漏洞,(2) 分析 React hook 依赖或性能模式,(3) 检测大型代码库中的结构反模式,(4) 需要超越手动检查的系统化模式匹配。
---

# AST-Grep Code Analysis

AST 模式匹配通过结构识别而非逐行阅读来发现代码问题。代码结构揭示了隐藏的关系、漏洞和反模式,这些是表面检查所无法发现的。

## Configuration

- **Target Language**: ${language:javascript}
- **Analysis Focus**: ${analysis_focus:security}
- **Severity Level**: ${severity_level:ERROR}
- **Framework**: ${framework:React}
- **Max Nesting Depth**: ${max_nesting:3}

## Prerequisites

```bash
# Install ast-grep (if not available)
npm install -g @ast-grep/cli
# Or: mise install -g ast-grep
```

## Decision Tree: When to Use AST Analysis

```
Code review needed?
|
+-- Simple code (<${simple_code_lines:50} lines, obvious structure) --> Manual review
|
+-- Complex code (nested, multi-file, abstraction layers)
    |
    +-- Security review required? --> Use security patterns
    +-- Performance analysis? --> Use performance patterns
    +-- Structural quality? --> Use structure patterns
    +-- Cross-file patterns? --> Run with --include glob
```

## Pattern Categories

| Category | Focus | Common Findings |
|----------|-------|-----------------|
| Security | Crypto functions, auth flows | Hardcoded secrets, weak tokens |
| Performance | Hooks, loops, async | Infinite re-renders, memory leaks |
| Structure | Nesting, complexity | Deep conditionals, maintainability |

## Essential Patterns

### Security: Hardcoded Secrets

```yaml
# sg-rules/security/hardcoded-secrets.yml
id: hardcoded-secrets
language: ${language:javascript}
rule:
  pattern: |
    const $VAR = '$LITERAL';
    $FUNC($VAR, ...)
  meta:
    severity: ${severity_level:ERROR}
    message: "Potential hardcoded secret detected"
```

### Security: Insecure Token Generation

```yaml
# sg-rules/security/insecure-tokens.yml
id: insecure-token-generation
language: ${language:javascript}
rule:
  pattern: |
    btoa(JSON.stringify($OBJ) + '.' + $SECRET)
  meta:
    severity: ${severity_level:ERROR}
    message: "Insecure token generation using base64"
```

### Performance: ${framework:React} Hook Dependencies

```yaml
# sg-rules/performance/react-hook-deps.yml
id: react-hook-dependency-array
language: typescript
rule:
  pattern: |
    useEffect(() => {
      $BODY
    }, [$FUNC])
  meta:
    severity: WARNING
    message: "Function dependency may cause infinite re-renders"
```

### Structure: Deep Nesting

```yaml
# sg-rules/structure/deep-nesting.yml
id: deep-nesting
language: ${language:javascript}
rule:
  any:
    - pattern: |
        if ($COND1) {
          if ($COND2) {
            if ($COND3) {
              $BODY
            }
          }
        }
    - pattern: |
        for ($INIT) {
          for ($INIT2) {
            for ($INIT3) {
              $BODY
            }
          }
        }
  meta:
    severity: WARNING
    message: "Deep nesting (>${max_nesting:3} levels) - consider refactoring"
```

## Running Analysis

```bash
# Security scan
ast-grep run -r sg-rules/security/

# Performance scan on ${framework:React} files
ast-grep run -r sg-rules/performance/ --include="*.tsx,*.jsx"

# Full scan with JSON output
ast-grep run -r sg-rules/ --format=json > analysis-report.json

# Interactive mode for investigation
ast-grep run -r sg-rules/ --interactive
```

## Pattern Writing Checklist

- [ ] Pattern matches specific anti-pattern, not general code
- [ ] Uses `inside` or `has` for context constraints
- [ ] Includes `not` constraints to reduce false positives
- [ ] Separate rules per language (JS vs TS)
- [ ] Appropriate severity (${severity_level:ERROR}/WARNING/INFO)

## Common Mistakes

| Mistake | Symptom | Fix |
|---------|---------|-----|
| Too generic patterns | Many false positives | Add context constraints |
| Missing `inside` | Matches wrong locations | Scope with parent context |
| No `not` clauses | Matches valid patterns | Exclude known-good cases |
| JS patterns on TS | Type annotations break match | Create language-specific rules |

## Verification Steps

1. **Test pattern accuracy**: Run on known-vulnerable code samples
2. **Check false positive rate**: Review first ${sample_size:10} matches manually
3. **Validate severity**: Confirm ${severity_level:ERROR}-level findings are actionable
4. **Cross-file coverage**: Verify pattern runs across intended scope

## Example Output

```
$ ast-grep run -r sg-rules/
src/components/UserProfile.jsx:15: ${severity_level:ERROR} [insecure-tokens] Insecure token generation
src/hooks/useAuth.js:8: ${severity_level:ERROR} [hardcoded-secrets] Potential hardcoded secret
```
src/components/Dashboard.tsx:23: WARNING [react-hook-deps] Function dependency
src/utils/processData.js:45: WARNING [deep-nesting] Deep nesting detected

发现 4 个问题(2 个错误,2 个警告)
```

## 项目设置

```bash
# 在项目中初始化 ast-grep
ast-grep init

# 创建规则目录
mkdir -p sg-rules/{security,performance,structure}

# 添加到 CI 流水线
# .github/workflows/lint.yml
# - run: ast-grep run -r sg-rules/ --format=json
```

## 自定义模式模板

### ${framework:React} 特定模式

```yaml
# 列表渲染中缺少 key
id: missing-list-key
language: typescript
rule:
  pattern: |
    $ARRAY.map(($ITEM) => <$COMPONENT $$$PROPS />)
  constraints:
    $PROPS:
      not:
        has:
          pattern: 'key={$_}'
  meta:
    severity: WARNING
    message: "列表渲染中缺少 key prop"
```

### Async/Await 模式

```yaml
# async 中缺少错误处理
id: unhandled-async
language: ${language:javascript}
rule:
  pattern: |
    async function $NAME($$$) {
      $$$BODY
    }
  constraints:
    $BODY:
      not:
        has:
          pattern: 'try { $$$ } catch'
  meta:
    severity: WARNING
    message: "缺少 try-catch 错误处理的 async 函数"
```

## 与 CI/CD 集成

```yaml
# GitHub Actions 示例
name: AST 分析
on: [push, pull_request]
jobs:
  analyze:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: 安装 ast-grep
        run: npm install -g @ast-grep/cli
      - name: 运行分析
        run: |
          ast-grep run -r sg-rules/ --format=json > report.json
          if grep -q '"severity": "${severity_level:ERROR}"' report.json; then
            echo "发现严重问题!"
            exit 1
          fi
```