Fix crash caused by modifying the UI from a background thread (#20275)

Author: mokagio

RELEASE-NOTES.txt

@@ -1,6 +1,16 @@
 21.9
 -----
 
+* [*] [internal] Refactored fetching posts in the Reader tab, including post related operations (i.e. like/unlike, save for latter, etc.) [#20197]
+* [**] Reader: Add a button in the post menu to block an author and stop seeing their posts. [#20193]
+* [**] [Jetpack-only] Jetpack individual plugin support: Warns user about sites with only individual plugins not supporting all features of the app yet and gives the ability to install the full Jetpack plugin. [#20223]
+* [**] [Jetpack-only] Help: Display the Jetpack app FAQ card on Help screen when switching from the WordPress app to the Jetpack app is complete. [#20232]
+* [***] [Jetpack-only] Blaze: We added support for Blaze in the app. The user can now promote a post or page from the app to reach new audiences. [#20253]
+
+21.8.1
+-----
+
+* [**] [internal] Fixes a crash that happens in the background when the weekly roundup notification is being processed. [#20275]
 
 21.8
 -----

WordPress/Classes/ViewRelated/Jetpack/Branding/Coordinator/JetpackFeaturesRemovalCoordinator.swift

@@ -115,20 +115,43 @@ class JetpackFeaturesRemovalCoordinator: NSObject {
     }
 
     /// Used to determine if the Jetpack features are enabled based on the current app UI type.
+    /// This way we ensure features are not removed before reloading the UI.
+    /// But if this function is called from a background thread, we determine if the Jetpack Features
+    /// are enabled based on the removal phase regardless of the app UI state.
     /// Default root view coordinator is used.
     @objc
     static func jetpackFeaturesEnabled() -> Bool {
+        guard Thread.isMainThread else {
+            return shouldEnableJetpackFeatures()
+        }
         return jetpackFeaturesEnabled(rootViewCoordinator: .shared)
     }
 
     /// Used to determine if the Jetpack features are enabled based on the current app UI type.
     /// This way we ensure features are not removed before reloading the UI.
+    /// But if this function is called from a background thread, we determine if the Jetpack Features
+    /// are enabled based on the removal phase regardless of the app UI state.
     /// Using two separate methods (rather than one method with a default argument) because Obj-C.
     /// - Returns: `true` if UI type is normal, and `false` if UI type is simplified.
     static func jetpackFeaturesEnabled(rootViewCoordinator: RootViewCoordinator) -> Bool {
+        guard Thread.isMainThread else {
+            return shouldEnableJetpackFeatures()
+        }
         return rootViewCoordinator.currentAppUIType == .normal
     }
 
+
+    /// Used to determine if the Jetpack features are enabled based on the removal phase regardless of the app UI state.
+    private static func shouldEnableJetpackFeatures(featureFlagStore: RemoteFeatureFlagStore = RemoteFeatureFlagStore()) -> Bool {
+        let phase = generalPhase()
+        switch phase {
+        case .four, .newUsers, .selfHosted:
+            return false
+        default:
+            return true
+        }
+    }
+
     /// Used to display feature-specific or feature-collection overlays.
     /// - Parameters:
     ///   - viewController: The view controller where the overlay should be presented in.