feat: added support to have navigator scoped screen model

voyager-core/src/commonMain/kotlin/cafe/adriel/voyager/core/model/ScreenModel.kt

@@ -30,6 +30,10 @@ public inline fun <reified T : ScreenModel> Screen.rememberScreenModel(
         ScreenModelStore.getOrPut(this, tag, factory)
     }
 
+public inline fun <reified T : ScreenModel> Screen.getScreenModel(
+    tag: String? = null
+): T? = ScreenModelStore.getOrNull(this, tag)
+
 public interface ScreenModel {
 
     public fun onDispose() {}

voyager-core/src/commonMain/kotlin/cafe/adriel/voyager/core/model/ScreenModelStore.kt

@@ -53,6 +53,15 @@ public object ScreenModelStore {
         return screenModels.getOrPut(key, factory) as T
     }
 
+    @PublishedApi
+    internal inline fun <reified T : ScreenModel> getOrNull(
+        screen: Screen,
+        tag: String?
+    ): T? {
+        val key = getKey<T>(screen, tag)
+        return screenModels[key] as? T
+    }
+
     public inline fun <reified T : Any> getOrPutDependency(
         screenModel: ScreenModel,
         name: String,

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

@@ -6,6 +6,7 @@ import cafe.adriel.voyager.core.lifecycle.DisposableEffectIgnoringConfiguration
 import cafe.adriel.voyager.core.stack.StackEvent
 import cafe.adriel.voyager.navigator.Navigator
 import cafe.adriel.voyager.navigator.lifecycle.NavigatorLifecycleStore
+import cafe.adriel.voyager.navigator.screen.NavigatorScreen
 
 private val disposableEvents: Set<StackEvent> =
     setOf(StackEvent.Pop, StackEvent.Replace)
@@ -77,6 +78,7 @@ internal fun disposeNavigator(navigator: Navigator) {
     for (screen in navigator.items) {
         navigator.dispose(screen)
     }
+    navigator.dispose(NavigatorScreen(navigator))
     NavigatorLifecycleStore.remove(navigator)
     navigator.clearEvent()
 }

voyager-navigator/src/commonMain/kotlin/cafe/adriel/voyager/navigator/lifecycle/NavigatorScreenModel.kt

@@ -0,0 +1,64 @@
+package cafe.adriel.voyager.navigator.lifecycle
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisallowComposableCalls
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import cafe.adriel.voyager.core.model.ScreenModel
+import cafe.adriel.voyager.core.model.getScreenModel
+import cafe.adriel.voyager.core.model.rememberScreenModel
+import cafe.adriel.voyager.core.screen.Screen
+import cafe.adriel.voyager.navigator.LocalNavigator
+import cafe.adriel.voyager.navigator.Navigator
+import cafe.adriel.voyager.navigator.currentOrThrow
+import cafe.adriel.voyager.navigator.screen.NavigatorScreen
+
+/**
+ * Lookup for a [ScreenModel] that was remembered in the current [LocalNavigator] or in your parents.
+ * If an instance was not found, an [IllegalStateException] will be thrown
+ *
+ * @param tag A custom tag used to "tag" the [ScreenModel]
+ * @throws IllegalStateException if now [ScreenModel] was found in [LocalNavigator] or in your parents
+ *
+ * @return The [ScreenModel] instance found
+ */
+@Suppress("UnusedReceiverParameter")
+@Throws(IllegalStateException::class)
+@Composable
+public inline fun <reified T : ScreenModel> Screen.navigatorScreenModel(
+    tag: String? = null
+): T {
+    val navigator = LocalNavigator.currentOrThrow
+    var screenModel: T? by remember(tag) { mutableStateOf(null) }
+    if (screenModel == null) {
+        screenModel = generateSequence(seed = navigator) { it.parent }
+            .mapNotNull { nav -> emptyScreen(nav).getScreenModel(tag) as? T }
+            .firstOrNull()
+    }
+    return checkNotNull(screenModel) {
+        "${T::class} was not found in $navigator and it parents"
+    }
+}
+
+/**
+ * Remember a [ScreenModel] that will be scoped to current [LocalNavigator]
+ *
+ * @param tag A custom tag used to "tag" the [ScreenModel]
+ * @param factory A function to create a new instance if one is not remembered yet
+ *
+ * @return The [ScreenModel] instance
+ */
+@Suppress("UnusedReceiverParameter")
+@Composable
+public inline fun <reified T : ScreenModel> Screen.rememberNavigatorScreenModel(
+    tag: String? = null,
+    crossinline factory: @DisallowComposableCalls () -> T
+): T {
+    val navigator = LocalNavigator.currentOrThrow
+    val screen = emptyScreen(navigator)
+    return screen.rememberScreenModel(tag, factory)
+}
+
+public fun emptyScreen(navigator: Navigator): Screen = NavigatorScreen(navigator)

voyager-navigator/src/commonMain/kotlin/cafe/adriel/voyager/navigator/screen/NavigatorScreen.kt

@@ -0,0 +1,23 @@
+package cafe.adriel.voyager.navigator.screen
+
+import androidx.compose.runtime.Composable
+import cafe.adriel.voyager.core.screen.Screen
+import cafe.adriel.voyager.core.screen.ScreenKey
+import cafe.adriel.voyager.navigator.Navigator
+
+/**
+ * An internal screen to be used as "key" to persist a [cafe.adriel.voyager.core.model.ScreenModel]
+ *
+ * @param navigator The current [Navigator] to be scoped
+ */
+internal data class NavigatorScreen(
+    private val navigator: Navigator
+) : Screen {
+
+    override val key: ScreenKey = "$navigator"
+
+    @Composable
+    override fun Content() {
+        error("Calling NavigatorScreen Content() fun is an error")
+    }
+}