Fixes a bug that cannot use custom scope viewModel in mvrx-compose.

[JSpiner]

What is bug?

mvrx-compose has a mavericksViewModel() function that can inject a viewModel from compose.

inline fun <reified VM : MavericksViewModel<S>, reified S : MavericksState> mavericksViewModel(
    **scope: LifecycleOwner = LocalLifecycleOwner.current,**
    noinline keyFactory: (() -> String)? = null,
    noinline argsFactory: (() -> Any?)? = null,
): VM {

In compose, it is necessary to manage viewModel with a different scope than fragment or activity for various reasons.
(ex: navigation component for compose)
So mavericksViewModel() is implemented to receive a custom scope as an argument.
However, when using mavericksViewModel in compose within a fragment, customScope is ignored and created as fragment scope.

if (parentFragment != null) {
    val args = argsFactory?.invoke() ?: parentFragment.arguments?.get(Mavericks.KEY_ARG)
    FragmentViewModelContext(activity, args, parentFragment) // viewModelStoreOwner, savedStateRegistry is ignored.
} else {
    val args = argsFactory?.invoke() ?: activity.intent.extras?.get(Mavericks.KEY_ARG)
    ActivityViewModelContext(activity, args, viewModelStoreOwner, savedStateRegistry)
}

This is because according to the internal implementation of mavericksViewModel, it ignores viewModelStoreOwner and saveStateRegistry if there is a parentFragment.
Looking at the Git history, it seems that when the maverickViewModel function was created, there were no viewModelStoreOwner and savedStateRegistry arguments in FragmentViewModelContext.

How to fix?

Simply adding to use viewModelStoreOwner and savedStateRegistry solved it.
(The fragment's viewModelStoreOwner and savedStateRegistry were used as the default arguments.)

What changed

1. I created some test code that fails.
   • I created a test for each activity and fragment to check whether the two customScopes create different viewModels.
   • Activity scope succeeds, fragment scope fails.
2. Pass custom viewModelStoreOwner and savedStateRegistry as arguments to FragmentViewModelContext.
3. I verified that the test was successful.

[elihart]

Thanks for the writeup, fix, and tests. Before merging, I want to ensure that this change won't break the way that anybody is using the code now. Can you think of anything in the change that might not be backwards compatible?

[JSpiner]

@elihart
That's a good point. I am confident that there are no backward compatibility issues for the following two reasons.

1. All existing and newly created tests passed.
2. For code that does not use a custom scope, it operates logically the same.
   • FragmentViewModelContext uses parentFragment's viewModelStoreOwner and savedStateRegistry as default parameters.
   • The parentFragment is retrieved by casting the scope to Fragment. https://github.com/airbnb/mavericks/blob/main/mvrx-compose/src/main/kotlin/com/airbnb/mvrx/compose/MavericksComposeExtensions.kt#L70
   • So scope.viewModelStoreOwner and parentFragment.viewModelStoreOwner are the same. The same goes for savedStateRegistry.

And for code that use a custom scope, It wouldn't have worked properly. So I fixed the bug.

[elihart]

Ok, great, thanks for that. I'll merge once checks pass