feat: support setting a Navigator key

voyager-navigator/src/commonMain/kotlin/cafe/adriel/voyager/navigator/Navigator.kt

@@ -3,6 +3,7 @@ package cafe.adriel.voyager.navigator
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.ProvidableCompositionLocal
+import androidx.compose.runtime.currentCompositeKeyHash
 import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
@@ -51,12 +52,14 @@ public fun Navigator(
     screen: Screen,
     disposeBehavior: NavigatorDisposeBehavior = NavigatorDisposeBehavior(),
     onBackPressed: OnBackPressed = { true },
+    key: String = compositionUniqueId(),
     content: NavigatorContent = { CurrentScreen() }
 ) {
     Navigator(
         screens = listOf(screen),
         disposeBehavior = disposeBehavior,
         onBackPressed = onBackPressed,
+        key = key,
         content = content,
     )
 }
@@ -66,14 +69,16 @@ public fun Navigator(
     screens: List<Screen>,
     disposeBehavior: NavigatorDisposeBehavior = NavigatorDisposeBehavior(),
     onBackPressed: OnBackPressed = { true },
+    key: String = compositionUniqueId(),
     content: NavigatorContent = { CurrentScreen() },
 ) {
     require(screens.isNotEmpty()) { "Navigator must have at least one screen" }
+    require(key.isNotEmpty()) { "Navigator key can't be empty" }
 
     CompositionLocalProvider(
         LocalNavigatorStateHolder providesDefault rememberSaveableStateHolder()
     ) {
-        val navigator = rememberNavigator(screens, disposeBehavior, LocalNavigator.current)
+        val navigator = rememberNavigator(screens, key, disposeBehavior, LocalNavigator.current)
 
         if (navigator.parent?.disposeBehavior?.disposeNestedNavigators != false) {
             NavigatorDisposableEffect(navigator)
@@ -95,6 +100,7 @@ public fun Navigator(
 
 public class Navigator @InternalVoyagerApi constructor(
     screens: List<Screen>,
+    @InternalVoyagerApi public val key: String,
     private val stateHolder: SaveableStateHolder,
     public val disposeBehavior: NavigatorDisposeBehavior,
     public val parent: Navigator? = null
@@ -180,3 +186,9 @@ public data class NavigatorDisposeBehavior(
     val disposeNestedNavigators: Boolean = true,
     val disposeSteps: Boolean = true,
 )
+
+@InternalVoyagerApi
+@Composable
+public fun compositionUniqueId(): String = currentCompositeKeyHash.toString(MaxSupportedRadix)
+
+private val MaxSupportedRadix = 36

voyager-navigator/src/commonMain/kotlin/cafe/adriel/voyager/navigator/NavigatorSaver.kt

@@ -15,6 +15,7 @@ public val LocalNavigatorSaver: ProvidableCompositionLocal<NavigatorSaver<*>> =
 public fun interface NavigatorSaver<Saveable : Any> {
     public fun saver(
         initialScreens: List<Screen>,
+        key: String,
         stateHolder: SaveableStateHolder,
         disposeBehavior: NavigatorDisposeBehavior,
         parent: Navigator?
@@ -32,9 +33,9 @@ public fun interface NavigatorSaver<Saveable : Any> {
  *
  * If you want to use only Parcelable and want a NavigatorSaver that forces the use Parcelable, you can use [parcelableNavigatorSaver].
  */
-public fun defaultNavigatorSaver(): NavigatorSaver<Any> = NavigatorSaver { _, stateHolder, disposeBehavior, parent ->
+public fun defaultNavigatorSaver(): NavigatorSaver<Any> = NavigatorSaver { _, key, stateHolder, disposeBehavior, parent ->
     listSaver(
         save = { navigator -> navigator.items },
-        restore = { items -> Navigator(items, stateHolder, disposeBehavior, parent) }
+        restore = { items -> Navigator(items, key, stateHolder, disposeBehavior, parent) }
     )
 }

voyager-navigator/src/commonMain/kotlin/cafe/adriel/voyager/navigator/internal/NavigatorSaverInternal.kt

@@ -17,16 +17,17 @@ internal val LocalNavigatorStateHolder: ProvidableCompositionLocal<SaveableState
 @Composable
 internal fun rememberNavigator(
     screens: List<Screen>,
+    key: String,
     disposeBehavior: NavigatorDisposeBehavior,
     parent: Navigator?,
 ): Navigator {
     val stateHolder = LocalNavigatorStateHolder.current
     val navigatorSaver = LocalNavigatorSaver.current
     val saver = remember(navigatorSaver, stateHolder, parent, disposeBehavior) {
-        navigatorSaver.saver(screens, stateHolder, disposeBehavior, parent)
+        navigatorSaver.saver(screens, key, stateHolder, disposeBehavior, parent)
     }
 
-    return rememberSaveable(saver = saver) {
-        Navigator(screens, stateHolder, disposeBehavior, parent)
+    return rememberSaveable(saver = saver, key = key) {
+        Navigator(screens, key, stateHolder, disposeBehavior, parent)
     }
 }