3 files changed, 84 insertions, 6 deletions
diff --git a/changelog.d/10238.removal b/changelog.d/10238.removal
new file mode 100644
index 0000000000..5fb7bfb47e
--- /dev/null
+++ b/changelog.d/10238.removal
@@ -0,0 +1 @@
+The current spam checker interface is deprecated in favour of a new generic modules system. See the [upgrade notes](https://github.com/matrix-org/synapse/blob/master/UPGRADE.rst#deprecation-of-the-current-spam-checker-interface) for more information on how to update to the new system.
diff --git a/synapse/events/spamcheck.py b/synapse/events/spamcheck.py
index 45ec96dfc1..efec16c226 100644
--- a/synapse/events/spamcheck.py
+++ b/synapse/events/spamcheck.py
@@ -109,6 +109,8 @@ def load_legacy_spam_checkers(hs: "synapse.server.HomeServer"):
             if f is None:
                 return None
 
+            wrapped_func = f
+
             if f.__name__ == "check_registration_for_spam":
                 checker_args = inspect.signature(f)
                 if len(checker_args.parameters) == 3:
@@ -133,19 +135,18 @@ def load_legacy_spam_checkers(hs: "synapse.server.HomeServer"):
                             request_info,
                         )
 
-                    f = wrapper
+                    wrapped_func = wrapper
                 elif len(checker_args.parameters) != 4:
                     raise RuntimeError(
                         "Bad signature for callback check_registration_for_spam",
                     )
 
             def run(*args, **kwargs):
-                # We've already made sure f is not None above, but mypy doesn't do well
-                # across function boundaries so we need to tell it f is definitely not
-                # None.
-                assert f is not None
+                # mypy doesn't do well across function boundaries so we need to tell it
+                # wrapped_func is definitely not None.
+                assert wrapped_func is not None
 
-                return maybe_awaitable(f(*args, **kwargs))
+                return maybe_awaitable(wrapped_func(*args, **kwargs))
 
             return run
 
diff --git a/tests/handlers/test_register.py b/tests/handlers/test_register.py
index a9fd3036dc..c5f6bc3c75 100644
--- a/tests/handlers/test_register.py
+++ b/tests/handlers/test_register.py
@@ -17,6 +17,7 @@ from unittest.mock import Mock
 from synapse.api.auth import Auth
 from synapse.api.constants import UserTypes
 from synapse.api.errors import Codes, ResourceLimitError, SynapseError
+from synapse.events.spamcheck import load_legacy_spam_checkers
 from synapse.spam_checker_api import RegistrationBehaviour
 from synapse.types import RoomAlias, UserID, create_requester
 
@@ -79,6 +80,39 @@ class BanBadIdPUser(TestSpamChecker):
         return RegistrationBehaviour.ALLOW
 
 
+class TestLegacyRegistrationSpamChecker:
+    def __init__(self, config, api):
+        pass
+
+    async def check_registration_for_spam(
+        self,
+        email_threepid,
+        username,
+        request_info,
+    ):
+        pass
+
+
+class LegacyAllowAll(TestLegacyRegistrationSpamChecker):
+    async def check_registration_for_spam(
+        self,
+        email_threepid,
+        username,
+        request_info,
+    ):
+        return RegistrationBehaviour.ALLOW
+
+
+class LegacyDenyAll(TestLegacyRegistrationSpamChecker):
+    async def check_registration_for_spam(
+        self,
+        email_threepid,
+        username,
+        request_info,
+    ):
+        return RegistrationBehaviour.DENY
+
+
 class RegistrationTestCase(unittest.HomeserverTestCase):
     """Tests the RegistrationHandler."""
 
@@ -95,6 +129,8 @@ class RegistrationTestCase(unittest.HomeserverTestCase):
 
         hs = self.setup_test_homeserver(config=hs_config)
 
+        load_legacy_spam_checkers(hs)
+
         module_api = hs.get_module_api()
         for module, config in hs.config.modules.loaded_modules:
             module(config=config, api=module_api)
@@ -537,6 +573,46 @@ class RegistrationTestCase(unittest.HomeserverTestCase):
 
     @override_config(
         {
+            "spam_checker": [
+                {
+                    "module": TestSpamChecker.__module__ + ".LegacyAllowAll",
+                }
+            ]
+        }
+    )
+    def test_spam_checker_legacy_allow(self):
+        """Tests that a legacy spam checker implementing the legacy 3-arg version of the
+        check_registration_for_spam callback is correctly called.
+
+        In this test and the following one we test both success and failure to make sure
+        any failure comes from the spam checker (and not something else failing in the
+        call stack) and any success comes from the spam checker (and not because a
+        misconfiguration prevented it from being loaded).
+        """
+        self.get_success(self.handler.register_user(localpart="user"))
+
+    @override_config(
+        {
+            "spam_checker": [
+                {
+                    "module": TestSpamChecker.__module__ + ".LegacyDenyAll",
+                }
+            ]
+        }
+    )
+    def test_spam_checker_legacy_deny(self):
+        """Tests that a legacy spam checker implementing the legacy 3-arg version of the
+        check_registration_for_spam callback is correctly called.
+
+        In this test and the previous one we test both success and failure to make sure
+        any failure comes from the spam checker (and not something else failing in the
+        call stack) and any success comes from the spam checker (and not because a
+        misconfiguration prevented it from being loaded).
+        """
+        self.get_failure(self.handler.register_user(localpart="user"), SynapseError)
+
+    @override_config(
+        {
             "modules": [
                 {
                     "module": TestSpamChecker.__module__ + ".BanAll",