Warn user if we raise with empty while not online

To avoid surprise by adding a warning. Right now, when offline, empty result is returned with no log nor error, see https://groups.google.com/forum/#!topic/google-cloud-firestore-discuss/puFl9HVU57I/discussion

1 files changed, 6 insertions, 0 deletions

diff --git a/Firestore/Source/Core/FSTEventManager.m b/Firestore/Source/Core/FSTEventManager.m
index 3e1b99b..ec03eb7 100644
--- a/Firestore/Source/Core/FSTEventManager.m
+++ b/Firestore/Source/Core/FSTEventManager.m
@@ -20,6 +20,7 @@
 #import "Firestore/Source/Core/FSTSyncEngine.h"
 #import "Firestore/Source/Model/FSTDocumentSet.h"
 #import "Firestore/Source/Util/FSTAssert.h"
+#import "Firestore/Source/Util/FSTLogger.h"
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -179,6 +180,11 @@ NS_ASSUME_NONNULL_BEGIN
     return NO;
   }
 
+  // Warn user if we raise initial event with empty documents while we are not actually online.
+  if (snapshot.documents.isEmpty && onlineState != FSTOnlineStateHealthy) {
+    FSTWarn(@"Could not reach Firestore backend.");
+  }
+
   // Raise data from cache if we have any documents or we are offline
   return !snapshot.documents.isEmpty || onlineState == FSTOnlineStateFailed;
 }