ast-grep-patterns

name	ast-grep-patterns
description	ast-grep (sg) cookbook for safe structural refactors in TS/TSX (rename, extract, find-replace with context). Triggers: "ast-grep", "structural replace", "rename symbol", "codemod tsx", "tim cau truc", "thay the theo pattern".

ast-grep-patterns — Structural Refactor Recipes

Step 0 — Check ast-grep is installed

command -v sg >/dev/null 2>&1 || command -v ast-grep >/dev/null 2>&1

If missing, ask user ONCE to install:

brew install ast-grep  # macOS
cargo install ast-grep --locked  # any OS with Rust

If user declines → fall back to Grep + per-file Edit (still works, slower).

Basic syntax:

sg run --lang tsx --pattern '<pattern>' --rewrite '<replacement>' --update-all
sg run -p '...' -r '...' --lang tsx    # shorter flags
sg scan --pattern '<pattern>'          # dry-run, just show matches

Meta-variables:

• $VAR — matches any single AST node (identifier, expression, etc.)
• $$$ — matches ANY number of nodes (for spread / arg lists)
• $$$ARGS — named multi-node capture

Pattern library

Rename a function/variable (identifier)

sg run --lang tsx -p 'oldName' -r 'newName' --update-all

⚠️ This matches the identifier in ALL contexts: calls, imports, properties. For precise scoping, use kind filter:

sg run --lang tsx -p 'function oldName($$$PARAMS) { $$$BODY }' -r 'function newName($$$PARAMS) { $$$BODY }' --update-all

Rename a React component + all JSX usages

# declaration
sg run --lang tsx -p 'function OldCard($$$P) { $$$B }' -r 'function NewCard($$$P) { $$$B }' --update-all
# JSX open tag
sg run --lang tsx -p '<OldCard $$$A />' -r '<NewCard $$$A />' --update-all
# JSX close tag
sg run --lang tsx -p '</OldCard>' -r '</NewCard>' --update-all
# imports
sg run --lang tsx -p 'OldCard' -r 'NewCard' --update-all

Change default export to named export

sg run --lang tsx -p 'export default function $NAME($$$P) { $$$B }' -r 'export function $NAME($$$P) { $$$B }' --update-all

Then find all default imports and switch to named:

sg run --lang tsx -p 'import $NAME from "$PATH"' -r 'import { $NAME } from "$PATH"' --update-all
# WARN: this is too broad — it'll break legit default imports from 3rd-party libs
# Prefer scoping by path prefix:
sg run --lang tsx -p 'import $NAME from "@/$REST"' -r 'import { $NAME } from "@/$REST"' --update-all

Replace console.log with a logger

sg run --lang ts -p 'console.log($$$ARGS)' -r 'logger.info($$$ARGS)' --update-all

Remove all console.log in production code (scoped)

sg scan --lang ts -p 'console.log($$$A)' --filter "file_path_matches:^src/" > matches.txt
# review matches.txt, then:
sg run --lang ts -p 'console.log($$$A)' -r '' --update-all

Wrap useState with a logger (for debugging)

sg run --lang tsx \
  -p 'const [$STATE, $SETTER] = useState($INIT)' \
  -r 'const [$STATE, $SETTER] = useState($INIT); console.log("$STATE:", $STATE)' \
  --update-all

Convert class components to functional (partial — simple case)

# very narrow pattern; not a general converter, just a starter
sg run --lang tsx \
  -p 'class $NAME extends React.Component { render() { return $JSX } }' \
  -r 'function $NAME() { return $JSX }' \
  --update-all

Swap library import path

sg run --lang tsx \
  -p 'import { $$$NAMES } from "@supabase/auth-helpers-nextjs"' \
  -r 'import { $$$NAMES } from "@supabase/ssr"' \
  --update-all

Add 'use client' directive to all files using useState

# step 1: find files
sg scan --lang tsx -p 'useState' --reporter files > client-files.txt
# step 2: for each, prepend 'use client' if not already there
while read f; do
  head -1 "$f" | grep -q "'use client'" || sed -i "1i 'use client'" "$f"
done < client-files.txt

Extract a JSX block into a component (partial)

ast-grep can find the block:

sg scan --lang tsx -p '<div className="card">$$$CHILDREN</div>' --json

But the extraction (create new file + replace with component usage) is multi-step — combine with Write/Edit tools.

Update import path (after moving file)

When you mv components/Old.tsx components/new/Old.tsx:

sg run --lang tsx -p '"@/components/Old"' -r '"@/components/new/Old"' --update-all
sg run --lang tsx -p "'@/components/Old'" -r "'@/components/new/Old'" --update-all

Config file approach

For complex projects, put patterns in sgconfig.yml:

ruleDirs:
  - sg-rules

Create sg-rules/rename-user.yml:

id: rename-getUser-to-fetchUser
language: tsx
rule:
  pattern: getUser
fix: fetchUser

Run:

sg scan   # preview
sg scan --update-all  # apply

Dry-run protocol

Always scan first:

sg scan --lang tsx -p '<pattern>' --reporter json | jq 'length'

Show user the count + a sample of 3 matches before running --update-all.

Gotchas

• Pattern matches too much → narrow with node-kind specifier: pattern: 'function $X() { $$ }' is more specific than $X
• String literals missed — ast-grep matches AST, so "oldName" is a string node, not an identifier; rename pattern must target strings separately
• Comments — ast-grep generally ignores comments; use grep + manual Edit for those
• Template literals with expressions need separate patterns from plain strings
• File encoding issues on Windows — ensure UTF-8 LF

Constraints

• Always sg scan first to count + preview before sg run --update-all
• Scope by language (--lang ts vs tsx) to avoid matching types in wrong context
• Commit state before any --update-all — easy revert path
• For >50 files affected, show count + confirm before executing
• Patterns with just $X (bare meta-var) are almost always too broad — resist