Feature request: Add support for app.runWithContext()

[posva]

This feature was introduced here and it's now used by vue router and pinia. Adding this will help people use the new feature

Here is a currently failing test using only vue test utils

  it('runWithContext', () => {
    let app: App
    const wrapper = mount(
      {
        template: `<HasInjection />`,
        setup() {
          provide('hello', 'component')
          return {}
        },
        components: {
          HasInjection: {
            setup() {
              const globalInjection = app!.runWithContext(() =>
                inject('hello', 'fallback')
              )
              const parentInjection = inject('hello', 'fallback')
              return { parentInjection, globalInjection }
            },
            template: `<div>{{ parentInjection }};{{ globalInjection }}</div>`,
          },
        },
      },
      {
        global: {
          provide: {
            hello: 'global',
          },
          plugins: [
            (a) => {
              app = a
            },
          ],
        },
      }
    )

    expect(wrapper.text()).toBe('component;global')
  })

[posva]

I added the failing test at https://github.com/vuejs/test-utils/tree/feat/runWithContext in case anybody wants to pick up the task

[cexbrayat]

I'm not yet familiar with this feature you implemented in core, but looking at
vuejs/core@869f3fb#diff-aba22e928f34a9ced3bf916c54a41b6facdfcb3e2caa18534dfae6d8a7e3cea6R56-R60
I thought this was expected if runWIthContext is in a component.

As instance will not be null, no? And in that case, the current app context will not be checked.
Or am I missing something obvious?

[posva]

I'm getting a different behavior within pinia but apparently it's the normal behavior. I think I must be forgetting something though. I wonder if it wouldn't be more consistent to give preference to the app within runWithContext, but that's a core thing anyway. Sorry 😅