Moai Tool Ast Grep

AST-Grep Integration

Structural code search, lint, and transformation tool using Abstract Syntax Tree analysis.

Quick Reference (30 seconds)

What is AST-Grep?

AST-Grep (sg) is a fast, polyglot tool for structural code search and transformation. Unlike regex-based search, it understands code syntax and matches patterns based on AST structure.

When to Use

• Searching for code patterns that regex cannot capture (e.g., nested function calls)
• Refactoring code across multiple files with semantic awareness
• Security scanning for vulnerability patterns (SQL injection, XSS, etc.)
• API migration and deprecation handling
• Enforcing code style rules at the syntax level

Core Commands

# Pattern search
sg run --pattern 'console.log($MSG)' --lang javascript src/

# Security scan with rules
sg scan --config sgconfig.yml

# Code transformation
sg run --pattern 'foo($A)' --rewrite 'bar($A)' --lang python src/

# Test rules
sg test

Pattern Syntax Basics

$VAR       - Matches any single AST node (meta-variable)
$$$ARGS    - Matches zero or more nodes (variadic)
$$_        - Matches any single node (anonymous)

Supported Languages

Python, JavaScript, TypeScript, Go, Rust, Java, Kotlin, C, C++, Ruby, Swift, C#, PHP, Scala, Elixir, Lua, HTML, Vue, Svelte, and 30+ more.

Implementation Guide (5 minutes)

Installation

# macOS
brew install ast-grep

# npm (cross-platform)
npm install -g @ast-grep/cli

# Cargo (Rust)
cargo install ast-grep

Basic Pattern Matching

Simple Pattern Search

# Find all console.log calls
sg run --pattern 'console.log($MSG)' --lang javascript

# Find all Python function definitions
sg run --pattern 'def $FUNC($$$ARGS): $$$BODY' --lang python

# Find React useState hooks
sg run --pattern 'useState($INIT)' --lang typescriptreact

Meta-variables

Meta-variables capture matching AST nodes:

# $NAME - Single node capture
pattern: 'const $NAME = require($PATH)'

# $$$ARGS - Variadic capture (zero or more)
pattern: 'function $NAME($$$ARGS) { $$$BODY }'

# $$_ - Anonymous single capture (don't care)
pattern: 'if ($$_) { return $VALUE }'

Code Transformation

Simple Rewrite

# Rename function
sg run --pattern 'oldFunc($ARGS)' --rewrite 'newFunc($ARGS)' --lang python

# Update API call
sg run --pattern 'axios.get($URL)' --rewrite 'fetch($URL)' --lang typescript

Complex Transformation with YAML Rules

# rule.yml
id: convert-var-to-const
language: javascript
rule:
  pattern: 'var $NAME = $VALUE'
fix: 'const $NAME = $VALUE'
message: 'Prefer const over var'
severity: warning

sg scan --rule rule.yml src/

Rule-Based Scanning

Configuration File (sgconfig.yml)

ruleDirs:
  - ./rules/security
  - ./rules/quality

testConfigs:
  - ./rules/**/__tests__/*.yml

languageGlobs:
  python: ['**/*.py']
  typescript: ['**/*.ts', '**/*.tsx']
  javascript: ['**/*.js', '**/*.jsx']

Security Rule Example

# rules/security/sql-injection.yml
id: sql-injection-risk
language: python
severity: error
message: 'Potential SQL injection vulnerability. Use parameterized queries.'
rule:
  any:
    - pattern: 'cursor.execute($QUERY % $ARGS)'
    - pattern: 'cursor.execute($QUERY.format($$$ARGS))'
    - pattern: 'cursor.execute(f"$$$SQL")'
fix: 'cursor.execute($QUERY, $ARGS)'

Relational Rules

Inside Rule (Scoped Search)

id: no-console-in-function
language: javascript
rule:
  pattern: 'console.log($$$ARGS)'
  inside:
    pattern: 'function $NAME($$$PARAMS) { $$$BODY }'

Has Rule (Contains Check)

id: async-without-await
language: javascript
rule:
  pattern: 'async function $NAME($$$PARAMS) { $$$BODY }'
  not:
    has:
      pattern: 'await $EXPR'
message: 'Async function without await'

Follows/Precedes Rules

id: missing-error-handling
language: go
rule:
  pattern: '$ERR := $CALL'
  not:
    follows:
      pattern: 'if $ERR != nil { $$$BODY }'

Composite Rules

id: complex-rule
language: typescript
rule:
  all:
    - pattern: 'useState($INIT)'
    - inside:
        pattern: 'function $COMPONENT($$$PROPS) { $$$BODY }'
    - not:
        precedes:
          pattern: 'useEffect($$$ARGS)'

Advanced Patterns

For comprehensive documentation including:

• Complex multi-file transformations
• Custom language configuration
• CI/CD integration patterns
• Performance optimization tips

See the following module files:

• modules/pattern-syntax.md - Complete pattern syntax reference
• modules/security-rules.md - Security scanning rule templates
• modules/refactoring-patterns.md - Common refactoring patterns
• modules/language-specific.md - Language-specific patterns

Context7 Integration

For latest AST-Grep documentation:

Step 1: Resolve library ID
Use mcp__context7__resolve-library-id with query "ast-grep"

Step 2: Fetch documentation
Use mcp__context7__get-library-docs with the resolved library ID

MoAI-ADK Integration

AST-Grep is integrated into MoAI-ADK through:

1. Tool Registry: Registered as AST_ANALYZER type in tool_registry.py
2. PostToolUse Hook: Automatic security scanning after Write/Edit operations
3. Permissions: Bash(sg:*) and Bash(ast-grep:*) auto-allowed

Running Scans

# Scan with MoAI-ADK rules
sg scan --config .claude/skills/moai-tool-ast-grep/rules/sgconfig.yml

# Scan specific directory
sg scan --config sgconfig.yml src/

# JSON output for CI/CD
sg scan --config sgconfig.yml --json > results.json

Works Well With

• moai-workflow-testing - TDD integration, test pattern detection
• moai-foundation-quality - TRUST 5 compliance, code quality gates
• moai-domain-backend - API pattern detection, security scanning
• moai-domain-frontend - React/Vue pattern optimization
• moai-lang-python - Python-specific security and style rules
• moai-lang-typescript - TypeScript type safety patterns

Related Agents

• expert-refactoring - AST-based large-scale refactoring
• expert-security - Security vulnerability scanning
• manager-quality - Code complexity analysis
• expert-debug - Pattern-based debugging

Reference

• AST-Grep Official Documentation
• AST-Grep GitHub Repository
• Pattern Playground
• Rule Configuration Reference