serverPrefetch hooks in mixins not called during SSR

[tabjy]

Version

3.0.4

Reproduction link

https://codesandbox.io/s/vue-ssr-bug-o1nbv?file=/src/index.js

Steps to reproduce

const MyComponent = defineComponent({
  name: "MyComponent",
  template: `<div>MyComponent</div>`,
  mixins: [
    {
      serverPrefetch() {
        console.log("mixin defined serverPrefetch call on", this.$options.name);
        return Promise.resolve();
      }
    }
  ]
});

The serverPrefetch hook mixed into MyComponent is not called during SSR.

What is expected?

When refreshing the SSR page, it is expected to see serverPrefetch hooks for both ComponentA (defined explicitly as a local option) and ComponentB (defined via a mixin) invoked by server renderer.

$ node index.js
serving on port 8080
locally defined serverPrefetch call on ComponentA
mixin defined serverPrefetch call on ComponentB

What is actually happening?

Only the locally defined hook for ComponentA is invoked:

$ node index.js
serving on port 8080
locally defined serverPrefetch call on ComponentA

---

I'm not very familiar with Vue. Sorry if this turns out to be an id10t error.

[tabjy]

Took a deeper look in the source. render.ts doesn't really check if there is any serverPrefetch defined in mixins. Is this an intentional design? It seems to be supported in vue 2 though.

[edison1105]

The logic for processing mixin serverPrefetch should be written here:
https://github.com/vuejs/vue-next/blob/8ac2241b22/packages/runtime-core/src/componentOptions.ts#L438

[tabjy]

Hey @edison1105! Thanks for the timely reply. So is it confirmed to be a bug of Vue 3?

I am not sure if writing serverPrefech processing logic where you pointed is a good idea. To my limited knowledge of Vue:

1. servePrefetch is only related to SSR, namely the server-renderer package. Being a not standard lifecycle, it feels questionable to process servePrefetch in the runtime-core package.

2. applyOptions deals with post-created lifecycles only, all of which are essentially noops for SSR.

Please correct me. It's very likely that I misunderstood something here and there...

[edison1105]

I'm think the best is to make it consistent with Vue 2.
https://github.com/vuejs/vue/blob/dev/src/core/util/options.js#L172

BTW, your code not handled globalMixins

[tabjy]

...make it consistent with Vue 2

Thank you for pointing the direction. I'll take a deeper look!

BTW, your code not handled globalMixins

No, it doesn't, and it doesn't handle mixins with a mixin either. By no means that was a proper fix. 😂

[edison1105]

@tabjy I think you can submit your PR if it is ready.

[tabjy]

@edison1105 I don't know the workflow here. I was under the impression submitting it after someone from @vuejs confirms it to be a bug and assigns me to it, but you're right. I might as well submit it now. Worst case they can just close it if it's a wontfix.

Thank you!

[HcySunYang]

@tabjy Thanks your PR, and sorry for being late.
The merge logic of the serverPrefect hook cannot be written in applyOptions, because applyOptions is controlled by __FEATURE_OPTIONS_API__, details can be found here feature-flags. I will take a closer look at this issue later.

[HcySunYang]

After this #3070, I think it's ok to define merge logic in applyOptions