feat(experimental): shouldTransform for ref-transform

packages/ref-transform/README.md

@@ -37,6 +37,17 @@ A few commonly used APIs have shorthands (which also removes the need to import
 
 This package is the lower-level transform that can be used standalone. Higher-level tooling (e.g. `@vitejs/plugin-vue` and `vue-loader`) will provide integration via options.
 
+### `shouldTransform`
+
+Can be used to do a cheap check to determine whether full transform should be performed.
+
+```js
+import { shouldTransform } from '@vue/ref-transform'
+
+shouldTransform(`let a = ref(0)`) // false
+shouldTransform(`let a = $ref(0)`) // true
+```
+
 ### `transform`
 
 ```js
@@ -66,6 +77,8 @@ interface RefTransformOptions {
 
 ### `transformAST`
 
+Transform with an existing Babel AST + MagicString instance. This is used internally by `@vue/compiler-sfc` to avoid double parse/transform cost.
+
 ```js
 import { transformAST } from '@vue/ref-transform'
 import { parse } from '@babel/parser'

packages/ref-transform/src/index.ts

@@ -24,6 +24,11 @@ import { babelParserDefaultPlugins } from '@vue/shared'
 const TO_VAR_SYMBOL = '$'
 const TO_REF_SYMBOL = '$$'
 const shorthands = ['ref', 'computed', 'shallowRef']
+const transformCheckRE = /[^\w]\$(?:\$|ref|computed|shallowRef)?\(/
+
+export function shouldTransform(src: string): boolean {
+  return transformCheckRE.test(src)
+}
 
 export interface ReactiveDeclarator {
   node: VariableDeclarator