Fix type errors introduced by new annotations in the Prometheus Client library. (#11832)

Co-authored-by: David Robertson <davidr@element.io>

1 files changed, 9 insertions, 1 deletions

diff --git a/synapse/metrics/__init__.py b/synapse/metrics/__init__.py
index 9e6c1b2f3b..cca084c18c 100644
--- a/synapse/metrics/__init__.py
+++ b/synapse/metrics/__init__.py
@@ -30,6 +30,7 @@ from typing import (
     Type,
     TypeVar,
     Union,
+    cast,
 )
 
 import attr
@@ -60,7 +61,7 @@ all_gauges: "Dict[str, Union[LaterGauge, InFlightGauge]]" = {}
 HAVE_PROC_SELF_STAT = os.path.exists("/proc/self/stat")
 
 
-class RegistryProxy:
+class _RegistryProxy:
     @staticmethod
     def collect() -> Iterable[Metric]:
         for metric in REGISTRY.collect():
@@ -68,6 +69,13 @@ class RegistryProxy:
                 yield metric
 
 
+# A little bit nasty, but collect() above is static so a Protocol doesn't work.
+# _RegistryProxy matches the signature of a CollectorRegistry instance enough
+# for it to be usable in the contexts in which we use it.
+# TODO Do something nicer about this.
+RegistryProxy = cast(CollectorRegistry, _RegistryProxy)
+
+
 @attr.s(slots=True, hash=True, auto_attribs=True)
 class LaterGauge: