[fenix] Change FxNimbus initialization sequence (https://github.com/mozilla-mobile/fenix/pull/25089)

* Change FxNimbus initialization sequence

* Add cache invalidation

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

@@ -72,6 +72,7 @@ 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 +394,8 @@ 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 })

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")