Allow selecting "prejoin" events by state keys (#14642)

* Declare new config

* Parse new config

* Read new config

* Don't use trial/our TestCase where it's not needed

Before:

```
$ time trial tests/events/test_utils.py > /dev/null

real	0m2.277s
user	0m2.186s
sys	0m0.083s
```

After:
```
$ time trial tests/events/test_utils.py > /dev/null

real	0m0.566s
user	0m0.508s
sys	0m0.056s
```

* Helper to upsert to event fields

without exceeding size limits.

* Use helper when adding invite/knock state

Now that we allow admins to include events in prejoin room state with
arbitrary state keys, be a good Matrix citizen and ensure they don't
accidentally create an oversized event.

* Changelog

* Move StateFilter tests

should have done this in #14668

* Add extra methods to StateFilter

* Use StateFilter

* Ensure test file enforces typed defs; alphabetise

* Workaround surprising get_current_state_ids

* Whoops, fix mypy

1 files changed, 145 insertions, 0 deletions

diff --git a/tests/config/test_api.py b/tests/config/test_api.py
new file mode 100644
index 0000000000..6773c9a277
--- /dev/null
+++ b/tests/config/test_api.py
@@ -0,0 +1,145 @@
+from unittest import TestCase as StdlibTestCase
+
+import yaml
+
+from synapse.config import ConfigError
+from synapse.config.api import ApiConfig
+from synapse.types.state import StateFilter
+
+DEFAULT_PREJOIN_STATE_PAIRS = {
+    ("m.room.join_rules", ""),
+    ("m.room.canonical_alias", ""),
+    ("m.room.avatar", ""),
+    ("m.room.encryption", ""),
+    ("m.room.name", ""),
+    ("m.room.create", ""),
+    ("m.room.topic", ""),
+}
+
+
+class TestRoomPrejoinState(StdlibTestCase):
+    def read_config(self, source: str) -> ApiConfig:
+        config = ApiConfig()
+        config.read_config(yaml.safe_load(source))
+        return config
+
+    def test_no_prejoin_state(self) -> None:
+        config = self.read_config("foo: bar")
+        self.assertFalse(config.room_prejoin_state.has_wildcards())
+        self.assertEqual(
+            set(config.room_prejoin_state.concrete_types()), DEFAULT_PREJOIN_STATE_PAIRS
+        )
+
+    def test_disable_default_event_types(self) -> None:
+        config = self.read_config(
+            """
+room_prejoin_state:
+    disable_default_event_types: true
+        """
+        )
+        self.assertEqual(config.room_prejoin_state, StateFilter.none())
+
+    def test_event_without_state_key(self) -> None:
+        config = self.read_config(
+            """
+room_prejoin_state:
+    disable_default_event_types: true
+    additional_event_types:
+        - foo
+        """
+        )
+        self.assertEqual(config.room_prejoin_state.wildcard_types(), ["foo"])
+        self.assertEqual(config.room_prejoin_state.concrete_types(), [])
+
+    def test_event_with_specific_state_key(self) -> None:
+        config = self.read_config(
+            """
+room_prejoin_state:
+    disable_default_event_types: true
+    additional_event_types:
+        - [foo, bar]
+        """
+        )
+        self.assertFalse(config.room_prejoin_state.has_wildcards())
+        self.assertEqual(
+            set(config.room_prejoin_state.concrete_types()),
+            {("foo", "bar")},
+        )
+
+    def test_repeated_event_with_specific_state_key(self) -> None:
+        config = self.read_config(
+            """
+room_prejoin_state:
+    disable_default_event_types: true
+    additional_event_types:
+        - [foo, bar]
+        - [foo, baz]
+        """
+        )
+        self.assertFalse(config.room_prejoin_state.has_wildcards())
+        self.assertEqual(
+            set(config.room_prejoin_state.concrete_types()),
+            {("foo", "bar"), ("foo", "baz")},
+        )
+
+    def test_no_specific_state_key_overrides_specific_state_key(self) -> None:
+        config = self.read_config(
+            """
+room_prejoin_state:
+    disable_default_event_types: true
+    additional_event_types:
+        - [foo, bar]
+        - foo
+        """
+        )
+        self.assertEqual(config.room_prejoin_state.wildcard_types(), ["foo"])
+        self.assertEqual(config.room_prejoin_state.concrete_types(), [])
+
+        config = self.read_config(
+            """
+room_prejoin_state:
+    disable_default_event_types: true
+    additional_event_types:
+        - foo
+        - [foo, bar]
+        """
+        )
+        self.assertEqual(config.room_prejoin_state.wildcard_types(), ["foo"])
+        self.assertEqual(config.room_prejoin_state.concrete_types(), [])
+
+    def test_bad_event_type_entry_raises(self) -> None:
+        with self.assertRaises(ConfigError):
+            self.read_config(
+                """
+room_prejoin_state:
+    additional_event_types:
+        - []
+            """
+            )
+
+        with self.assertRaises(ConfigError):
+            self.read_config(
+                """
+room_prejoin_state:
+    additional_event_types:
+        - [a]
+            """
+            )
+
+        with self.assertRaises(ConfigError):
+            self.read_config(
+                """
+room_prejoin_state:
+    additional_event_types:
+        - [a, b, c]
+            """
+            )
+
+        with self.assertRaises(ConfigError):
+            self.read_config(
+                """
+room_prejoin_state:
+    additional_event_types:
+        - [true, 1.23]
+            """
+            )