Root BackHandler possible bug

[TepesLucian]

Having an issue in the following scenario. The root screen sometimes has a BackHandler like so:

@Composable
fun RootUi(
  state: TestState,
  modifier: Modifier,
) {
  RootContent()
  BackHandler {
    // don't let the user out of the app just yet
  }
}

At some point ScreenA is pushed to the backstack which has the following logic in its presenter:

navigator.apply {
   pop() // or resetRoot(ScreenRoot)
   goTo(ScreenB)
}

Effectively I want ScreenA to pop and to push ScreenB. Tapping android back button in ScreenB calls BackHandler on RootUi from my testing even thought it's not visible on the screen. Removing BackHandler navigation logic works as expected and navigates back to ScreenRoot.

[TepesLucian]

Managed to write a test case that fails : 0e7467e

[saket]

This is such a weird bug. The code enters an infinite loop between the BackHandler calling the navigator and the navigator calling the system back dispatcher. I wish the framework protected us from re-entrant callbacks. For now, is the only way to solve this by calling Activity#finish() directly from onRootPop?

[TepesLucian]

Tried the workaround but it doesn't seem to fix anything. My issue is not when root ui is present on screen but when ScreenA pops itself and pushes ScreenB. Pressing back in ScreenB should pop to RootUi but instead it calls BackHandler from RootUi even though it is not present on the screen. BackHandler from RootUi should be disabled since its ui is not on the screen. It's probably a race condition due to ScreenA popping itself and immediately pushing ScreenB.

[aschulz90]

If you check the layout inspector, do you see both screens in the hierarchy?
If you use AndroidPredictiveBackNavigationDecoration, then the two topmost screens are part of the layout hierarchy, to be able to peek at it.

[TepesLucian]

Looked into layout inspector and not seeing the RootUi in there, only once you start swiping back. Not sure why its BackHandler still lives on. I've tried commenting out decoration from NavigableCircuitContent and everything works as expected : navigating back makes ScreenB go to RootUi instead of calling BackHandler in RootUi.