5 files changed, 78 insertions, 7 deletions
diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 965478d8d5..8c3acff03e 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -137,12 +137,42 @@ class Config(object):
             return file_stream.read()
 
     def invoke_all(self, name, *args, **kargs):
+        """Invoke all instance methods with the given name and arguments in the
+        class's MRO.
+
+        Args:
+            name (str): Name of function to invoke
+            *args
+            **kwargs
+
+        Returns:
+            list: The list of the return values from each method called
+        """
         results = []
         for cls in type(self).mro():
             if name in cls.__dict__:
                 results.append(getattr(cls, name)(self, *args, **kargs))
         return results
 
+    @classmethod
+    def invoke_all_static(cls, name, *args, **kargs):
+        """Invoke all static methods with the given name and arguments in the
+        class's MRO.
+
+        Args:
+            name (str): Name of function to invoke
+            *args
+            **kwargs
+
+        Returns:
+            list: The list of the return values from each method called
+        """
+        results = []
+        for c in cls.mro():
+            if name in c.__dict__:
+                results.append(getattr(c, name)(*args, **kargs))
+        return results
+
     def generate_config(
         self,
         config_dir_path,
@@ -202,6 +232,23 @@ class Config(object):
         Returns: Config object.
         """
         config_parser = argparse.ArgumentParser(description=description)
+        cls.add_arguments_to_parser(config_parser)
+        obj, _ = cls.load_config_with_parser(config_parser, argv)
+
+        return obj
+
+    @classmethod
+    def add_arguments_to_parser(cls, config_parser):
+        """Adds all the config flags to an ArgumentParser.
+
+        Doesn't support config-file-generation: used by the worker apps.
+
+        Used for workers where we want to add extra flags/subcommands.
+
+        Args:
+            config_parser (ArgumentParser): App description
+        """
+
         config_parser.add_argument(
             "-c",
             "--config-path",
@@ -219,9 +266,29 @@ class Config(object):
             " Defaults to the directory containing the last config file",
         )
 
-        obj = cls()
+        # We can only invoke `add_arguments` on an actual object, but
+        # `add_arguments` should be side effect free so this is probably fine.
+        cls.invoke_all_static("add_arguments", config_parser)
 
-        obj.invoke_all("add_arguments", config_parser)
+    @classmethod
+    def load_config_with_parser(cls, config_parser, argv):
+        """Parse the commandline and config files with the given parser
+
+        Doesn't support config-file-generation: used by the worker apps.
+
+        Used for workers where we want to add extra flags/subcommands.
+
+        Args:
+            config_parser (ArgumentParser)
+            argv (list[str])
+
+        Returns:
+            tuple[HomeServerConfig, argparse.Namespace]: Returns the parsed
+            config object and the parsed argparse.Namespace object from
+            `config_parser.parse_args(..)`
+        """
+
+        obj = cls()
 
         config_args = config_parser.parse_args(argv)
 
@@ -244,7 +311,7 @@ class Config(object):
 
         obj.invoke_all("read_arguments", config_args)
 
-        return obj
+        return obj, config_args
 
     @classmethod
     def load_or_generate_config(cls, description, argv):
diff --git a/synapse/config/database.py b/synapse/config/database.py
index bcb2089dd7..746a6cd1f4 100644
--- a/synapse/config/database.py
+++ b/synapse/config/database.py
@@ -69,7 +69,8 @@ class DatabaseConfig(Config):
             if database_path is not None:
                 self.database_config["args"]["database"] = database_path
 
-    def add_arguments(self, parser):
+    @staticmethod
+    def add_arguments(parser):
         db_group = parser.add_argument_group("database")
         db_group.add_argument(
             "-d",
diff --git a/synapse/config/logger.py b/synapse/config/logger.py
index 0f5554211c..40502a5798 100644
--- a/synapse/config/logger.py
+++ b/synapse/config/logger.py
@@ -103,7 +103,8 @@ class LoggingConfig(Config):
         if args.log_file is not None:
             self.log_file = args.log_file
 
-    def add_arguments(cls, parser):
+    @staticmethod
+    def add_arguments(parser):
         logging_group = parser.add_argument_group("logging")
         logging_group.add_argument(
             "-v",
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 34cb11468c..c3de7a4e32 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -237,7 +237,8 @@ class RegistrationConfig(Config):
             % locals()
         )
 
-    def add_arguments(self, parser):
+    @staticmethod
+    def add_arguments(parser):
         reg_group = parser.add_argument_group("registration")
         reg_group.add_argument(
             "--enable-registration",
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 2a74dea2ea..080d0630bd 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -639,7 +639,8 @@ class ServerConfig(Config):
         if args.print_pidfile is not None:
             self.print_pidfile = args.print_pidfile
 
-    def add_arguments(self, parser):
+    @staticmethod
+    def add_arguments(parser):
         server_group = parser.add_argument_group("server")
         server_group.add_argument(
             "-D",