ast-grep Rule Crafter

ast-grep uses tree-sitter to parse code into AST, enabling precise pattern matching. Rules are defined in YAML for linting, searching, and rewriting code.

Quick Start

id: no-console-log
language: JavaScript
rule:
  pattern: console.log($$$ARGS)
fix: logger.log($$$ARGS)
message: Replace console.log with logger

Project Configuration

项目级扫描需要 sgconfig.yml 配置文件：

# sgconfig.yml (项目根目录)
ruleDirs:
  - rules          # 规则目录，递归加载所有 .yml 文件

典型项目结构：

my-project/
├── sgconfig.yml
├── rules/
│   ├── no-console.yml
│   └── custom/
│       └── team-rules.yml
└── src/

运行项目扫描：

ast-grep scan              # 自动查找 sgconfig.yml
ast-grep scan --config path/to/sgconfig.yml  # 指定配置

注意: ast-grep scan 命令必须有 sgconfig.yml，而 ast-grep run -p 可单独使用。

Rule Workflow

Lint Rule (常见)

只检查不修复，用于 CI/编辑器提示：

# rules/no-console-log.yml
id: no-console-log
language: JavaScript
severity: warning
message: Avoid console.log in production code
rule:
  pattern: console.log($$$ARGS)

验证：

ast-grep scan -r rules/no-console-log.yml src/

Rewrite Rule (可选)

需要自动修复时添加 fix：

id: no-console-log
language: JavaScript
severity: warning
message: Replace console.log with logger
rule:
  pattern: console.log($$$ARGS)
fix: logger.log($$$ARGS)

应用修复：

ast-grep scan -r rules/no-console-log.yml --update-all src/

开发流程

- [ ] 1. 用 CLI 探索 pattern: ast-grep -p 'pattern' src/
- [ ] 2. 创建规则文件 (.yml)
- [ ] 3. 验证: ast-grep scan -r rule.yml src/
- [ ] 4. 如有误报 → 添加 constraints → 重新验证

调试 AST 结构：

ast-grep -p 'console.log($ARG)' --debug-query ast

Essential Syntax

Element	Syntax	Example
Single node	$VAR	console.log($MSG)
Multiple nodes	$$$ARGS	fn($$$ARGS)
Same content	Use same name	$A == $A
Non-capturing	$_VAR	$_FN($_FN)

Core Rules Quick Reference

Type	Purpose	Example
pattern	Match code structure	pattern: if ($COND) {}
kind	Match AST node type	kind: function_declaration
all	Match ALL conditions	all: [pattern: X, kind: Y]
any	Match ANY condition	any: [pattern: var $A, pattern: let $A]
not	Exclude matches	not: {pattern: safe_call()}
has	Must have child	has: {kind: return_statement}
inside	Must be in ancestor	inside: {kind: class_body}

Detailed References

Complete syntax guide: See references/rule-syntax.md

• Atomic rules (pattern, kind, regex, nthChild, range)
• Composite rules (all, any, not, matches)
• Relational rules (has, inside, follows, precedes)
• Transform and fixConfig

Language-specific patterns: See references/common-patterns.md

• JavaScript/TypeScript examples
• Python examples
• Go and Rust examples

Supported Languages

Bash, C, Cpp, CSharp, Css, Elixir, Go, Haskell, Hcl, Html, Java, JavaScript, Json, Kotlin, Lua, Nix, Php, Python, Ruby, Rust, Scala, Solidity, Swift, Tsx, TypeScript, Yaml