mypy plugin: accept Literals in caches

scripts-dev/mypy_synapse_plugin.py

@@ -45,6 +45,7 @@ from mypy.types import (
     AnyType,
     CallableType,
     Instance,
+    LiteralType,
     NoneType,
     Options,
     TupleType,
@@ -813,6 +814,10 @@ def is_cacheable(
     if isinstance(rt, AnyType):
         return True, ("may be mutable" if verbose else None)
 
+    elif isinstance(rt, LiteralType):
+        # Literal[True] etc
+        return True, None
+
     elif isinstance(rt, Instance):
         if (
             rt.type.fullname in IMMUTABLE_VALUE_TYPES