prevent new users from downloading accidentally

anki/sync.py

@@ -634,6 +634,7 @@ class FullSyncer(HttpSyncer):
 
     def download(self):
         runHook("sync", "download")
+        localNotEmpty = self.col.db.scalar("select 1 from cards")
         self.col.close()
         cont = self.req("download")
         tpath = self.col.path + ".tmp"
@@ -644,7 +645,12 @@ class FullSyncer(HttpSyncer):
         # check the received file is ok
         d = DB(tpath)
         assert d.scalar("pragma integrity_check") == "ok"
+        remoteEmpty = not d.scalar("select 1 from cards")
         d.close()
+        # accidental clobber?
+        if localNotEmpty and remoteEmpty:
+            os.unlink(tpath)
+            return "downloadClobber"
         # overwrite existing collection
         os.unlink(self.col.path)
         os.rename(tpath, self.col.path)

aqt/sync.py

@@ -142,6 +142,8 @@ sync again to correct the issue."""))
             pass
         elif evt == "fullSync":
             self._confirmFullSync()
+        elif evt == "downloadClobber":
+            showInfo(_("Your AnkiWeb collection does not contain any cards. Please sync again and choose 'Upload' instead."))
         elif evt == "send":
             # posted events not guaranteed to arrive in order
             self.sentBytes = max(self.sentBytes, int(args[0]))
@@ -431,7 +433,10 @@ class SyncThread(QThread):
                 if not self.client.upload():
                     self.fireEvent("upbad")
             else:
-                self.client.download()
+                ret = self.client.download()
+                if ret == "downloadClobber":
+                    self.fireEvent(ret)
+                    return
         except Exception as e:
             if "sync cancelled" in str(e):
                 return