fix: should only check assignment when is left of assignment

Author: yyx990803

Diff for: packages/reactivity-transform/__tests__/reactivityTransform.spec.ts

@@ -509,5 +509,12 @@ describe('errors', () => {
         foo++
       `)
     ).toThrow(`Assignment to constant variable.`)
+
+    expect(() =>
+      transform(`
+      const foo = $ref(0)
+      bar = foo
+      `)
+    ).not.toThrow()
   })
 })

Diff for: packages/reactivity-transform/src/reactivityTransform.ts

@@ -548,7 +548,7 @@ export function transformAST(
       if (binding) {
         if (
           binding.isConst &&
-          (parent.type === 'AssignmentExpression' ||
+          ((parent.type === 'AssignmentExpression' && id === parent.left) ||
             parent.type === 'UpdateExpression')
         ) {
           error(`Assignment to constant variable.`, id)