Vue 2.7.0-beta.4 new Vue(...) return type becomes never when using setup() in the root instance

[danielwaltz]

Version

2.7.0-beta.4

Reproduction link

github.com

Steps to reproduce

After initializing a new Vue 2.7 project using the new Vite Vue 2 plugin with Volar take-over mode enabled, defining a setup() function in the root Vue instance changes the return type to never, leading to calling .$mount('#app') displaying a type error both in VSCode and when running vue-tsc.

new Vue({
  router,
  render: (h) => h(App)
  // No issues
}).$mount('#app');

new Vue({
  router,
  setup() {
    provide('test', 'value');
  },
  render: (h) => h(App)
  // Property '$mount' does not exist on type 'never'.
}).$mount('#app');

Happening both under TypeScript version 4.6.4 and 4.7.4.

What is expected?

Defining a setup function in the root instance works without changing the return type to never.

What is actually happening?

Using setup in the root displays a type error when trying to call $mount().

---

I believe everything is working fine in runtime, purely a TypeScript issue from what I can tell.

EDIT: Some additional info, I found that returning an empty object can work around this issue:

new Vue({
  router,
  setup() {
    provide('test', 'value');
    return {};
  },
  render: (h) => h(App)
  // No issues
}).$mount('#app');