SystemStats: Use 'identifierForVendor' for iOS device ID generation

BREAKING-CHANGES.txt

@@ -4,6 +4,30 @@ JUCE breaking changes
 develop
 =======
 
+Change
+------
+Unique device IDs on iOS now use the OS provided 'identifierForVendor'.
+OnlineUnlockStatus has been updated to handle the iOS edge-case where a device
+ID query might return an empty String.
+
+Possible Issues
+---------------
+The License checks using InAppPurchases, getLocalMachineIDs(), and
+getUniqueDeviceID() may return an empty String if iOS 'is not ready'. This can
+occur for example if the device has restarted but has not yet been unlocked.
+
+Workaround
+----------
+InAppPurchase has been updated to handle this and propagate the error
+accordingly. The relevant methods have been updated to return a Result object
+that can be queried for additional information on failure.
+
+Rationale
+---------
+Apple have introduced restrictions on device identification rendering our
+previous methods unsuitable.
+
+
 Change
 ------
 AudioProcessor::getAAXPluginIDForMainBusConfig() has been deprecated.

modules/juce_core/native/juce_SystemStats_mac.mm

@@ -351,6 +351,7 @@ int SystemStats::getPageSize()
 
 String SystemStats::getUniqueDeviceID()
 {
+   #if JUCE_MAC
     constexpr mach_port_t port = 0;
 
     const auto dict = IOServiceMatching ("IOPlatformExpertDevice");
@@ -363,6 +364,14 @@ String SystemStats::getUniqueDeviceID()
             if (CFGetTypeID (uuidTypeRef.get()) == CFStringGetTypeID())
                 return String::fromCFString ((CFStringRef) uuidTypeRef.get()).removeCharacters ("-");
     }
+   #elif JUCE_IOS
+    JUCE_AUTORELEASEPOOL
+    {
+        if (UIDevice* device = [UIDevice currentDevice])
+            if (NSUUID* uuid = [device identifierForVendor])
+                return nsStringToJuce ([uuid UUIDString]);
+    }
+   #endif
 
     return "";
 }

modules/juce_core/system/juce_SystemStats.h

@@ -153,7 +153,13 @@ public:
         changes.
 
         This ID will be invalidated by changes to the motherboard and CPU on non-mobile
-        platforms, or resetting an Android device.
+        platforms, or performing a system restore on an Android device.
+
+        There are some extra caveats on iOS: The returned ID is unique to the vendor part of
+        your  'Bundle Identifier' and is stable for all associated apps. The key is invalidated
+        once all associated apps are uninstalled. This function can return an empty string
+        under certain conditions, for example, If the device has not been unlocked since a
+        restart.
     */
     static String getUniqueDeviceID();