Move config check to read_config

synapse/config/appservice.py

@@ -33,20 +33,21 @@ class AppServiceConfig(Config):
 
     def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         self.app_service_config_files = config.get("app_service_config_files", [])
+        if not isinstance(self.app_service_config_files, list):
+            # type-ignore: this function gets arbitrary json value; we do use this path.
+            raise ConfigError(
+                "Expected '%s' to be a list of AS config files:"
+                % (self.app_service_config_files),
+                "app_service_config_files"
+            )
+
         self.track_appservice_user_ips = config.get("track_appservice_user_ips", False)
 
 
 def load_appservices(
     hostname: str, config_files: List[str]
 ) -> List[ApplicationService]:
     """Returns a list of Application Services from the config files."""
-    if not isinstance(config_files, list):
-        # type-ignore: this function gets arbitrary json value; we do use this path.
-        raise ConfigError(
-            "Expected '%s' to be a list of AS config files:"
-            % (config_files)
-            "app_service_config_files"
-        )
 
     # Dicts of value -> filename
     seen_as_tokens: Dict[str, str] = {}