AST Code Analysis Superpower

Prompt

---
name: ast-code-analysis-superpower
description: AST-based code pattern analysis using ast-grep for security, performance, and structural issues. Use when (1) reviewing code for security vulnerabilities, (2) analyzing React hook dependencies or performance patterns, (3) detecting structural anti-patterns across large codebases, (4) needing systematic pattern matching beyond manual inspection.
---

# AST-Grep Code Analysis

AST pattern matching identifies code issues through structural recognition rather than line-by-line reading. Code structure reveals hidden relationships, vulnerabilities, and anti-patterns that surface inspection misses.

## 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

# 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

# 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

# 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

# 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

# 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

Found 4 issues (2 errors, 2 warnings)

Project Setup

# Initialize ast-grep in project
ast-grep init

# Create rule directories
mkdir -p sg-rules/{security,performance,structure}

# Add to CI pipeline
# .github/workflows/lint.yml
# - run: ast-grep run -r sg-rules/ --format=json

Custom Pattern Templates

${framework:React} Specific Patterns

# Missing key in list rendering
id: missing-list-key
language: typescript
rule:
  pattern: |
    $ARRAY.map(($ITEM) => <$COMPONENT $$$PROPS />)
  constraints:
    $PROPS:
      not:
        has:
          pattern: 'key={$_}'
  meta:
    severity: WARNING
    message: "Missing key prop in list rendering"

Async/Await Patterns

# Missing error handling in async
id: unhandled-async
language: ${language:javascript}
rule:
  pattern: |
    async function $NAME($$$) {
      $$$BODY
    }
  constraints:
    $BODY:
      not:
        has:
          pattern: 'try { $$$ } catch'
  meta:
    severity: WARNING
    message: "Async function without try-catch error handling"

Integration with CI/CD

# GitHub Actions example
name: AST Analysis
on: [push, pull_request]
jobs:
  analyze:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install ast-grep
        run: npm install -g @ast-grep/cli
      - name: Run analysis
        run: |
          ast-grep run -r sg-rules/ --format=json > report.json
          if grep -q '"severity": "${severity_level:ERROR}"' report.json; then
            echo "Critical issues found!"
            exit 1
          fi

## How to Use

Copy the prompt above and paste it into ChatGPT, Claude, or any AI assistant. Replace any placeholder text in brackets with your specific details.

## Compatible Models

GPT-4o, Claude 3.5, Gemini, DeepSeek, Llama 3