IssueTracker

Component used:
android.arch.navigation:navigation-fragment-ktx
android.arch.navigation:navigation-ui-ktx

Version used:
1.0.0-alpha05

Devices/Android versions reproduced on:
-SM-A510F, Android 7.0
-Emulator x86_64 API 28

Sample project:
https://github.com/roccadev/NavPopBug

Description:

Having this structure:

nav_graph.xml
<navigation
    android:id="@+id/nav_graph"
    app:startDestination="@id/startFragment">

    <fragment
        android:id="@+id/startFragment"
        android:name="com.example.navbug.StartFragment"
        android:label="StartFragment"
        tools:layout="@layout/fragment_start">
        <action
            android:id="@+id/action_startFragment_to_nested_nav_graph"
            app:destination="@id/nested_nav_graph" />
    </fragment>
    <include app:graph="@navigation/nested_nav_graph" />
</navigation>

nested_nav_graph.xml
<navigation
    android:id="@+id/nested_nav_graph"
    app:startDestination="@id/nestedStartFragment">

    <fragment
        android:id="@+id/nestedStartFragment"
        android:name="com.example.navbug.NestedStartFragment"
        android:label="NestedStartFragment">
        <action
            android:id="@+id/action_nestedStartFragment_to_nestedSecondFragment"
            app:destination="@id/nestedSecondFragment"
            app:popUpTo="@+id/nestedStartFragment"
            app:popUpToInclusive="true" />
    </fragment>
    <fragment
        android:id="@+id/nestedSecondFragment"
        android:name="com.example.navbug.NestedSecondFragment"
        android:label="NestedSecondFragment" />
</navigation>

I want to achieve this navigation pattern:
StartFragment => NestedStartFragment => NestedSecondFragment =(back)=> StartFragment

I'm trying to implement this by setting the action NestedStartFragment=>NestedSecondFragment with the options [popUpTo=NestedStartFragment, popUpToInclusive=true], so that the resulting stack would be:
0. NestedSecondFragment
1. NestedNavGraph
2. StartFragment
3. NavGraph

When navigating from NestedStartFragment to NestedSecondFragment, the following execption occurs:
java.lang.IllegalArgumentException: Navigator androidx.navigation.fragment.FragmentNavigator@ccc9092 reported navigation to unknown destination id com.example.navbug:id/nestedSecondFragment
        at androidx.navigation.NavController$2.onNavigatorNavigated(NavController.java:142)
        at androidx.navigation.Navigator.dispatchOnNavigatorNavigated(Navigator.java:217)
        at androidx.navigation.fragment.FragmentNavigator.navigate(FragmentNavigator.java:207)
        at androidx.navigation.fragment.FragmentNavigator.navigate(FragmentNavigator.java:45)
        at androidx.navigation.NavDestination.navigate(NavDestination.java:407)
        at androidx.navigation.NavController.navigate(NavController.java:683)
        at androidx.navigation.NavController.navigate(NavController.java:630)
        at androidx.navigation.NavController.navigate(NavController.java:618)
        at com.example.navbug.NestedStartFragment$onViewCreated$1.onClick(Fragments.kt:31)
        at android.view.View.performClick(View.java:6597)
        at android.view.View.performClickInternal(View.java:6574)
        at android.view.View.access$3100(View.java:778)
        at android.view.View$PerformClick.run(View.java:25885)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Right before the navigation, the stack is:
0. NestedStartFragment
1. NestedNavGraph
2. StartFragment
3. NavGraph
When NestedStartFragment is popped on my request, NestedNavGraph is also popped because
"// We never want to leave NavGraphs on the top of the stack" (from NavController.onNavigatorNavigated)
with the effect that eventually the requested destination NestedSecondFragment is pruned from the graph and cannot be reached anymore.
Unless I'm doing something wrong, it seems that NavGraph automatic popping should be avoided if the final destination actually belongs to it.