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That function located in the hilt-navigation-compose artifact is not public nor intended for usage with arbitrary factory ViewModelStoreOwner and SavedStateRegistryOwner, its used only via the hiltViewModel() compose functions. The reality is that we can't accept two parameters of each owner since the user might wrongly pass different owners with different lifecycles which would cause trouble.

I think what you are asking is more along the lines of:

@Composable
fun <T> createHiltViewModelFactory(owner: T, args: Bundle) : ViewModelProvider.Factory?
 where T : ViewModelStoreOwner, T : SavedStateRegistryOwner, T : HasDefaultViewModelProviderFactory {
    return dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.createInternal(
        LocalContext.current.unwrap(),
        owner,
        args,
        owner.defaultViewModelProviderFactory,
    )
 }

where the owner is both a view model store owner and saved state owner. I think we could offer that API if there is a use-case for it...

Note that we want to offer the flexibility of creating the HiltViewModelFactory in a simpler way, just via a ViewModelStoreOwner, but it requires decoupling the implicit contract of ViewModelStoreOwner and SavedStateRegistryOwner and more specifically allow creating SavedStateHandles without forcing a factory subclass, see https://android-review.googlesource.com/c/platform/frameworks/support/+/1775329 for more details on this API proposal.

Yes, that is correct.

Technically, requiring a "SavedStateRegistryOwner that is also a ViewModelStoreOwner" is not unprecedented, viewmodel-savedstate requires it here: https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:lifecycle/lifecycle-viewmodel-savedstate/src/main/java/androidx/lifecycle/SavedStateHandleController.java;l=79?q=savedstatehan

With the release of creation extras we can clean this up avoiding the saved state and vm owner disparity and loss of default args, since by just taking a VM owner the matching args and saved state owner will be available in the creation extras.