fix: handle case of ref declaration without initial value

packages/compiler-sfc/__tests__/__snapshots__/compileScript.spec.ts.snap

@@ -292,6 +292,7 @@ exports[`SFC compile <script setup> ref: syntax sugar convert ref declarations 1
 
 export function setup() {
 
+      const foo = ref()
       const a = ref(1)
       const b = ref({
         count: 0
@@ -299,7 +300,7 @@ export function setup() {
       let c = () => {}
       let d
       
-return { a, b, c, d }
+return { foo, a, b, c, d }
 }
 
 export default { setup }"

packages/compiler-sfc/__tests__/compileScript.spec.ts

@@ -259,6 +259,7 @@ describe('SFC compile <script setup>', () => {
   describe('ref: syntax sugar', () => {
     test('convert ref declarations', () => {
       const { content, bindings } = compile(`<script setup>
+      ref: foo
       ref: a = 1
       ref: b = {
         count: 0
@@ -267,7 +268,10 @@ describe('SFC compile <script setup>', () => {
       let d
       </script>`)
       expect(content).toMatch(`import { ref } from 'vue'`)
+      expect(content).not.toMatch(`ref: foo`)
       expect(content).not.toMatch(`ref: a`)
+      expect(content).not.toMatch(`ref: b`)
+      expect(content).toMatch(`const foo = ref()`)
       expect(content).toMatch(`const a = ref(1)`)
       expect(content).toMatch(`
       const b = ref({
@@ -279,6 +283,7 @@ describe('SFC compile <script setup>', () => {
       expect(content).toMatch(`let d`)
       assertCode(content)
       expect(bindings).toStrictEqual({
+        foo: 'setup',
         a: 'setup',
         b: 'setup',
         c: 'setup',