Make sure to only add one of INBOX, SPAM, TRASH labels

The gmail API fails with an error otherwise.

fixes gauteh#26

README.md

@@ -111,3 +111,5 @@ You can get an [api key](https://console.developers.google.com/flows/enableapi?a
 The GMail API does not let you sync `muted` messages. Until the [Google
 bug](https://issuetracker.google.com/issues/36759067) is fixed, the `mute` and `muted` tags are not synchronized with the remote.
 
+Only one of the tags `inbox`, `spam`, and `trash` may be added to an email. For
+the time being, `trash` will be prefered over `spam`, and `spam` over inbox.

lieer/remote.py

@@ -435,6 +435,18 @@ def update (self, gmsg, nmsg, last_hist, force):
           self.all_updated = False
           return None
 
+      if 'TRASH' in add:
+        if 'SPAM' in add:
+          print ("update: %s: Trying to add both TRASH and SPAM, dropping SPAM (add: %s, rem: %s)" % (mid, add, rem))
+          add.remove('SPAM')
+        if 'INBOX' in add:
+          print ("update: %s: Trying to add both TRASH and INBOX, dropping INBOX (add: %s, rem: %s)" % (mid, add, rem))
+          add.remove('INBOX')
+      elif 'SPAM' in add:
+        if 'INBOX' in add:
+          print ("update: %s: Trying to add both SPAM and INBOX, dropping INBOX (add: %s, rem: %s)" % (mid, add, rem))
+          add.remove('INBOX')
+
       if self.dry_run:
         print ("(dry-run) mid: %s: add: %s, remove: %s" % (mid, str(add), str(rem)))
         return None