Enable v2 message attachments via toggle in internal settings

Signal/src/ViewControllers/AppSettings/Internal/InternalSettingsViewController.swift

@@ -91,6 +91,13 @@ class InternalSettingsViewController: OWSTableViewController2 {
             }
         ))
 
+        if FeatureFlags.v2MessageAttachmentsToggle && !AttachmentFeatureFlags.readMessages {
+            debugSection.add(.actionItem(withText: "DANGER!!! Enable encrypted message attachments (and exit)") {
+                AttachmentFeatureFlags.enableV2ForMessages()
+                fatalError("Intentionally crashing to restart app")
+            })
+        }
+
         if FeatureFlags.messageBackupFileAlpha {
             debugSection.add(.actionItem(withText: "Export Message Backup proto") {
                 self.exportMessageBackupProto()

SignalServiceKit/Messages/Attachments/V2/AttachmentManager/TSResource/AttachmentFeatureFlags.swift

@@ -13,8 +13,24 @@ public enum AttachmentFeatureFlags {
     public static let readStories = true
     public static let writeStories = true
 
-    public static let readMessages = false
-    public static let writeMessages = false
+    public static var readMessages: Bool {
+        FeatureFlags.v2MessageAttachmentsForceEnable
+            || UserDefaults.standard.bool(forKey: enableForMessagesKey)
+    }
+    public static var writeMessages: Bool {
+        FeatureFlags.v2MessageAttachmentsForceEnable
+            || UserDefaults.standard.bool(forKey: enableForMessagesKey)
+    }
 
-    public static let incrementalMigration = false
+    public static var incrementalMigration: Bool {
+        FeatureFlags.v2MessageAttachmentsForceEnable
+            || UserDefaults.standard.bool(forKey: enableForMessagesKey)
+    }
+
+    private static let enableForMessagesKey = "AttachmentFeatureFlags_enableForMessages"
+
+    public static func enableV2ForMessages() {
+        guard FeatureFlags.v2MessageAttachmentsToggle else { return }
+        UserDefaults.standard.set(true, forKey: enableForMessagesKey)
+    }
 }

SignalServiceKit/Util/FeatureFlags.swift

@@ -73,6 +73,9 @@ public class FeatureFlags: NSObject {
     public static let messageBackupFileAlpha = build.includes(.internal)
     public static let messageBackupFileAlphaRegistrationFlow = build.includes(.dev)
 
+    public static let v2MessageAttachmentsToggle = build.includes(.internal)
+    public static let v2MessageAttachmentsForceEnable = build.includes(.dev)
+
     public static let callLinkCreate = build.includes(.dev)
 
     public static let callRaiseHandReceiveSupport = build.includes(.production)