TM iOS: Support @synthesize methodQueue auto queue creation

Summary: Some native modules defined `synthesize methodQueue` which will ask the bridge to create a new serial queue for them. TM system needs to preserve this behavior for backward compatibility. In the future though, this magic shall be removed.

Reviewed By: mdvacca

Differential Revision: D15748198

fbshipit-source-id: 66a4b60a2769ac967a8d3bb00c4c635a68daebbc

ReactCommon/turbomodule/core/platform/ios/RCTTurboModuleManager.mm

@@ -289,6 +289,30 @@ static Class getFallbackClassFromName(const char *name)
     }
   }
 
+  /**
+   * Some modules need their own queues, but don't provide any, so we need to create it for them.
+   * These modules typically have the following:
+   *   `@synthesize methodQueue = _methodQueue`
+   */
+  if ([module respondsToSelector:@selector(methodQueue)]) {
+    dispatch_queue_t methodQueue = [module performSelector:@selector(methodQueue)];
+    if (!methodQueue) {
+      NSString *moduleClassName = NSStringFromClass(module.class);
+      NSString *queueName = [NSString stringWithFormat:@"com.facebook.react.%@Queue", moduleClassName];
+      methodQueue = dispatch_queue_create(queueName.UTF8String, DISPATCH_QUEUE_SERIAL);
+      @try {
+        [(id)module setValue:methodQueue forKey:@"methodQueue"];
+      } @catch (NSException *exception) {
+        RCTLogError(
+            @"TM: %@ is returning nil for its methodQueue, which is not "
+             "permitted. You must either return a pre-initialized "
+             "queue, or @synthesize the methodQueue to let the bridge "
+             "create a queue for you.",
+            moduleClassName);
+      }
+    }
+  }
+
   /**
    * Broadcast that this TurboModule was created.
    *