1 files changed, 7 insertions, 5 deletions
diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index 0dba997a23..d2fd29acb4 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -20,7 +20,7 @@ import os
 import platform
 import threading
 import time
-from typing import Dict, Union
+from typing import Callable, Dict, Iterable, Optional, Tuple, Union
 
 import six
 
@@ -59,10 +59,12 @@ class RegistryProxy(object):
 @attr.s(hash=True)
 class LaterGauge(object):
 
-    name = attr.ib()
-    desc = attr.ib()
-    labels = attr.ib(hash=False)
-    caller = attr.ib()
+    name = attr.ib(type=str)
+    desc = attr.ib(type=str)
+    labels = attr.ib(hash=False, type=Optional[Iterable[str]])
+    # callback: should either return a value (if there are no labels for this metric),
+    # or dict mapping from a label tuple to a value
+    caller = attr.ib(type=Callable[[], Union[Dict[Tuple[str, ...], float], float]])
 
     def collect(self):