[fenix] Change FxNimbus/Nimbus startup sequence (https://github.com/mozilla-mobile/fenix/pull/25266)

* Change FxNimbus initialization sequence

Add cache invalidation

* Change ordering of message restoration and Nimbus initialization

* Address reviewer comments

app/src/main/java/org/mozilla/fenix/FenixApplication.kt

@@ -45,6 +45,7 @@ import mozilla.components.service.glean.net.ConceptFetchHttpUploader
 import mozilla.components.support.base.facts.register
 import mozilla.components.support.base.log.Log
 import mozilla.components.support.base.log.logger.Logger
+import mozilla.components.support.base.observer.Observable
 import mozilla.components.support.ktx.android.content.isMainProcess
 import mozilla.components.support.ktx.android.content.runOnlyInMainProcess
 import mozilla.components.support.locale.LocaleAwareApplication
@@ -72,6 +73,7 @@ import org.mozilla.fenix.components.toolbar.ToolbarPosition
 import org.mozilla.fenix.ext.isCustomEngine
 import org.mozilla.fenix.ext.isKnownSearchDomain
 import org.mozilla.fenix.ext.settings
+import org.mozilla.fenix.nimbus.FxNimbus
 import org.mozilla.fenix.perf.MarkersActivityLifecycleCallbacks
 import org.mozilla.fenix.perf.ProfilerMarkerFactProcessor
 import org.mozilla.fenix.perf.StartupTimeline
@@ -393,7 +395,8 @@ open class FenixApplication : LocaleAwareApplication(), Provider {
     private fun setupMegazord(): Deferred<Unit> {
         // Note: Megazord.init() must be called as soon as possible ...
         Megazord.init()
-
+        // Give the generated FxNimbus a closure to lazily get the Nimbus object
+        FxNimbus.initialize { components.analytics.experiments }
         return GlobalScope.async(Dispatchers.IO) {
             // ... but RustHttpConfig.setClient() and RustLog.enable() can be called later.
             RustHttpConfig.setClient(lazy { components.core.client })
@@ -401,10 +404,31 @@ open class FenixApplication : LocaleAwareApplication(), Provider {
             // We want to ensure Nimbus is initialized as early as possible so we can
             // experiment on features close to startup.
             // But we need viaduct (the RustHttp client) to be ready before we do.
-            components.analytics.experiments.initialize()
+            components.analytics.experiments.apply {
+                initialize()
+                setupNimbusObserver(this)
+            }
         }
     }
 
+    private fun setupNimbusObserver(nimbus: Observable<NimbusInterface.Observer>) {
+        nimbus.register(object : NimbusInterface.Observer {
+            override fun onUpdatesApplied(updated: List<EnrolledExperiment>) {
+                onNimbusStartupAndUpdate()
+            }
+        })
+
+        onNimbusStartupAndUpdate()
+    }
+
+    private fun onNimbusStartupAndUpdate() {
+        val settings = settings()
+        if (FeatureFlags.messagingFeature && settings.isExperimentationEnabled) {
+            components.appStore.dispatch(AppAction.MessagingAction.Restore)
+        }
+        reportHomeScreenSectionMetrics(settings)
+    }
+
     override fun onTrimMemory(level: Int) {
         super.onTrimMemory(level)
 
@@ -738,6 +762,11 @@ open class FenixApplication : LocaleAwareApplication(), Provider {
 
     @VisibleForTesting
     internal fun reportHomeScreenMetrics(settings: Settings) {
+        reportOpeningScreenMetrics(settings)
+        reportHomeScreenSectionMetrics(settings)
+    }
+
+    private fun reportOpeningScreenMetrics(settings: Settings) {
         CustomizeHome.openingScreen.set(
             when {
                 settings.alwaysOpenTheHomepageWhenOpeningTheApp -> "homepage"
@@ -746,21 +775,18 @@ open class FenixApplication : LocaleAwareApplication(), Provider {
                 else -> ""
             }
         )
-        components.analytics.experiments.register(object : NimbusInterface.Observer {
-            override fun onExperimentsFetched() {
-                if (FeatureFlags.messagingFeature && settings().isExperimentationEnabled) {
-                    components.appStore.dispatch(AppAction.MessagingAction.Restore)
-                }
-            }
-            override fun onUpdatesApplied(updated: List<EnrolledExperiment>) {
-                CustomizeHome.jumpBackIn.set(settings.showRecentTabsFeature)
-                CustomizeHome.recentlySaved.set(settings.showRecentBookmarksFeature)
-                CustomizeHome.mostVisitedSites.set(settings.showTopSitesFeature)
-                CustomizeHome.recentlyVisited.set(settings.historyMetadataUIFeature)
-                CustomizeHome.pocket.set(settings.showPocketRecommendationsFeature)
-                CustomizeHome.contile.set(settings.showContileFeature)
-            }
-        })
+    }
+
+    private fun reportHomeScreenSectionMetrics(settings: Settings) {
+        // These settings are backed by Nimbus features.
+        // We break them out here so they can be recorded when
+        // `nimbus.applyPendingExperiments()` is called.
+        CustomizeHome.jumpBackIn.set(settings.showRecentTabsFeature)
+        CustomizeHome.recentlySaved.set(settings.showRecentBookmarksFeature)
+        CustomizeHome.mostVisitedSites.set(settings.showTopSitesFeature)
+        CustomizeHome.recentlyVisited.set(settings.historyMetadataUIFeature)
+        CustomizeHome.pocket.set(settings.showPocketRecommendationsFeature)
+        CustomizeHome.contile.set(settings.showContileFeature)
     }
 
     protected fun recordOnInit() {

app/src/main/java/org/mozilla/fenix/components/Analytics.kt

@@ -124,9 +124,7 @@ class Analytics(
     }
 
     val experiments: NimbusApi by lazyMonitored {
-        createNimbus(context, BuildConfig.NIMBUS_ENDPOINT).also { api ->
-            FxNimbus.api = api
-        }
+        createNimbus(context, BuildConfig.NIMBUS_ENDPOINT)
     }
 
     val messagingStorage by lazyMonitored {

app/src/main/java/org/mozilla/fenix/experiments/NimbusSetup.kt

@@ -13,11 +13,26 @@ import mozilla.components.service.nimbus.NimbusAppInfo
 import mozilla.components.service.nimbus.NimbusDisabled
 import mozilla.components.service.nimbus.NimbusServerSettings
 import mozilla.components.support.base.log.logger.Logger
+import org.mozilla.experiments.nimbus.NimbusInterface
+import org.mozilla.experiments.nimbus.internal.EnrolledExperiment
 import org.mozilla.experiments.nimbus.internal.NimbusException
 import org.mozilla.fenix.BuildConfig
 import org.mozilla.fenix.R
 import org.mozilla.fenix.ext.components
 import org.mozilla.fenix.ext.settings
+import org.mozilla.fenix.nimbus.FxNimbus
+
+/**
+ * Fenix specific observer of Nimbus events.
+ *
+ * The generated code `FxNimbus` provides a cache which should be invalidated
+ * when the experiments recipes are updated.
+ */
+private val observer = object : NimbusInterface.Observer {
+    override fun onUpdatesApplied(updated: List<EnrolledExperiment>) {
+        FxNimbus.invalidateCachedValues()
+    }
+}
 
 @Suppress("TooGenericExceptionCaught")
 fun createNimbus(context: Context, url: String?): NimbusApi {
@@ -69,6 +84,10 @@ fun createNimbus(context: Context, url: String?): NimbusApi {
             )
         )
         Nimbus(context, appInfo, serverSettings, errorReporter).apply {
+            // We register our own internal observer for housekeeping the Nimbus SDK and
+            // generated code.
+            register(observer)
+
             // This performs the minimal amount of work required to load branch and enrolment data
             // into memory. If `getExperimentBranch` is called from another thread between here
             // and the next nimbus disk write (setting `globalUserParticipation` or

app/src/test/java/org/mozilla/fenix/settings/SettingsFragmentTest.kt

@@ -11,7 +11,6 @@ import io.mockk.mockk
 import io.mockk.mockkObject
 import kotlinx.coroutines.test.advanceUntilIdle
 import mozilla.components.concept.fetch.Client
-import mozilla.components.service.nimbus.NimbusDisabled
 import mozilla.components.support.test.robolectric.testContext
 import mozilla.components.support.test.rule.MainCoroutineRule
 import mozilla.components.support.test.rule.runTestOnMain
@@ -30,7 +29,6 @@ import org.mozilla.fenix.ext.components
 import org.mozilla.fenix.ext.getPreferenceKey
 import org.mozilla.fenix.ext.settings
 import org.mozilla.fenix.helpers.FenixRobolectricTestRunner
-import org.mozilla.fenix.nimbus.FxNimbus
 import org.mozilla.fenix.utils.Settings
 import org.robolectric.Robolectric
 import java.io.IOException
@@ -56,8 +54,6 @@ class SettingsFragmentTest {
         mockkObject(Config)
         every { Config.channel } returns ReleaseChannel.Nightly
 
-        FxNimbus.api = NimbusDisabled(testContext)
-
         val activity = Robolectric.buildActivity(FragmentActivity::class.java).create().get()
         activity.supportFragmentManager.beginTransaction()
             .add(settingsFragment, "test")