Implementation for MSC3664: Pushrules for relations (#11804)

10 files changed, 454 insertions, 17 deletions

diff --git a/changelog.d/11804.feature b/changelog.d/11804.feature
new file mode 100644
index 0000000000..6420393541
--- /dev/null
+++ b/changelog.d/11804.feature
@@ -0,0 +1 @@
+Implement [MSC3664](https://github.com/matrix-org/matrix-doc/pull/3664). Contributed by Nico.
diff --git a/rust/src/push/base_rules.rs b/rust/src/push/base_rules.rs
index 63240cacfc..49802fa4eb 100644
--- a/rust/src/push/base_rules.rs
+++ b/rust/src/push/base_rules.rs
@@ -25,6 +25,7 @@ use crate::push::Action;
 use crate::push::Condition;
 use crate::push::EventMatchCondition;
 use crate::push::PushRule;
+use crate::push::RelatedEventMatchCondition;
 use crate::push::SetTweak;
 use crate::push::TweakValue;
 
@@ -115,6 +116,22 @@ pub const BASE_APPEND_OVERRIDE_RULES: &[PushRule] = &[
         default_enabled: true,
     },
     PushRule {
+        rule_id: Cow::Borrowed("global/override/.im.nheko.msc3664.reply"),
+        priority_class: 5,
+        conditions: Cow::Borrowed(&[Condition::Known(KnownCondition::RelatedEventMatch(
+            RelatedEventMatchCondition {
+                key: Some(Cow::Borrowed("sender")),
+                pattern: None,
+                pattern_type: Some(Cow::Borrowed("user_id")),
+                rel_type: Cow::Borrowed("m.in_reply_to"),
+                include_fallbacks: None,
+            },
+        ))]),
+        actions: Cow::Borrowed(&[Action::Notify, HIGHLIGHT_ACTION, SOUND_ACTION]),
+        default: true,
+        default_enabled: true,
+    },
+    PushRule {
         rule_id: Cow::Borrowed("global/override/.m.rule.contains_display_name"),
         priority_class: 5,
         conditions: Cow::Borrowed(&[Condition::Known(KnownCondition::ContainsDisplayName)]),
diff --git a/rust/src/push/evaluator.rs b/rust/src/push/evaluator.rs
index 0365dd01dc..cedd42c54d 100644
--- a/rust/src/push/evaluator.rs
+++ b/rust/src/push/evaluator.rs
@@ -23,6 +23,7 @@ use regex::Regex;
 use super::{
     utils::{get_glob_matcher, get_localpart_from_id, GlobMatchType},
     Action, Condition, EventMatchCondition, FilteredPushRules, KnownCondition,
+    RelatedEventMatchCondition,
 };
 
 lazy_static! {
@@ -49,6 +50,13 @@ pub struct PushRuleEvaluator {
     /// The power level of the sender of the event, or None if event is an
     /// outlier.
     sender_power_level: Option<i64>,
+
+    /// The related events, indexed by relation type. Flattened in the same manner as
+    /// `flattened_keys`.
+    related_events_flattened: BTreeMap<String, BTreeMap<String, String>>,
+
+    /// If msc3664, push rules for related events, is enabled.
+    related_event_match_enabled: bool,
 }
 
 #[pymethods]
@@ -60,6 +68,8 @@ impl PushRuleEvaluator {
         room_member_count: u64,
         sender_power_level: Option<i64>,
         notification_power_levels: BTreeMap<String, i64>,
+        related_events_flattened: BTreeMap<String, BTreeMap<String, String>>,
+        related_event_match_enabled: bool,
     ) -> Result<Self, Error> {
         let body = flattened_keys
             .get("content.body")
@@ -72,6 +82,8 @@ impl PushRuleEvaluator {
             room_member_count,
             notification_power_levels,
             sender_power_level,
+            related_events_flattened,
+            related_event_match_enabled,
         })
     }
 
@@ -156,6 +168,9 @@ impl PushRuleEvaluator {
             KnownCondition::EventMatch(event_match) => {
                 self.match_event_match(event_match, user_id)?
             }
+            KnownCondition::RelatedEventMatch(event_match) => {
+                self.match_related_event_match(event_match, user_id)?
+            }
             KnownCondition::ContainsDisplayName => {
                 if let Some(dn) = display_name {
                     if !dn.is_empty() {
@@ -239,6 +254,79 @@ impl PushRuleEvaluator {
         compiled_pattern.is_match(haystack)
     }
 
+    /// Evaluates a `related_event_match` condition. (MSC3664)
+    fn match_related_event_match(
+        &self,
+        event_match: &RelatedEventMatchCondition,
+        user_id: Option<&str>,
+    ) -> Result<bool, Error> {
+        // First check if related event matching is enabled...
+        if !self.related_event_match_enabled {
+            return Ok(false);
+        }
+
+        // get the related event, fail if there is none.
+        let event = if let Some(event) = self.related_events_flattened.get(&*event_match.rel_type) {
+            event
+        } else {
+            return Ok(false);
+        };
+
+        // If we are not matching fallbacks, don't match if our special key indicating this is a
+        // fallback relation is not present.
+        if !event_match.include_fallbacks.unwrap_or(false)
+            && event.contains_key("im.vector.is_falling_back")
+        {
+            return Ok(false);
+        }
+
+        // if we have no key, accept the event as matching, if it existed without matching any
+        // fields.
+        let key = if let Some(key) = &event_match.key {
+            key
+        } else {
+            return Ok(true);
+        };
+
+        let pattern = if let Some(pattern) = &event_match.pattern {
+            pattern
+        } else if let Some(pattern_type) = &event_match.pattern_type {
+            // The `pattern_type` can either be "user_id" or "user_localpart",
+            // either way if we don't have a `user_id` then the condition can't
+            // match.
+            let user_id = if let Some(user_id) = user_id {
+                user_id
+            } else {
+                return Ok(false);
+            };
+
+            match &**pattern_type {
+                "user_id" => user_id,
+                "user_localpart" => get_localpart_from_id(user_id)?,
+                _ => return Ok(false),
+            }
+        } else {
+            return Ok(false);
+        };
+
+        let haystack = if let Some(haystack) = event.get(&**key) {
+            haystack
+        } else {
+            return Ok(false);
+        };
+
+        // For the content.body we match against "words", but for everything
+        // else we match against the entire value.
+        let match_type = if key == "content.body" {
+            GlobMatchType::Word
+        } else {
+            GlobMatchType::Whole
+        };
+
+        let mut compiled_pattern = get_glob_matcher(pattern, match_type)?;
+        compiled_pattern.is_match(haystack)
+    }
+
     /// Match the member count against an 'is' condition
     /// The `is` condition can be things like '>2', '==3' or even just '4'.
     fn match_member_count(&self, is: &str) -> Result<bool, Error> {
@@ -267,8 +355,15 @@ impl PushRuleEvaluator {
 fn push_rule_evaluator() {
     let mut flattened_keys = BTreeMap::new();
     flattened_keys.insert("content.body".to_string(), "foo bar bob hello".to_string());
-    let evaluator =
-        PushRuleEvaluator::py_new(flattened_keys, 10, Some(0), BTreeMap::new()).unwrap();
+    let evaluator = PushRuleEvaluator::py_new(
+        flattened_keys,
+        10,
+        Some(0),
+        BTreeMap::new(),
+        BTreeMap::new(),
+        true,
+    )
+    .unwrap();
 
     let result = evaluator.run(&FilteredPushRules::default(), None, Some("bob"));
     assert_eq!(result.len(), 3);
diff --git a/rust/src/push/mod.rs b/rust/src/push/mod.rs
index 0dabfab8b8..d57800aa4a 100644
--- a/rust/src/push/mod.rs
+++ b/rust/src/push/mod.rs
@@ -267,6 +267,8 @@ pub enum Condition {
 #[serde(tag = "kind")]
 pub enum KnownCondition {
     EventMatch(EventMatchCondition),
+    #[serde(rename = "im.nheko.msc3664.related_event_match")]
+    RelatedEventMatch(RelatedEventMatchCondition),
     ContainsDisplayName,
     RoomMemberCount {
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -299,6 +301,20 @@ pub struct EventMatchCondition {
     pub pattern_type: Option<Cow<'static, str>>,
 }
 
+/// The body of a [`Condition::RelatedEventMatch`]
+#[derive(Serialize, Deserialize, Debug, Clone)]
+pub struct RelatedEventMatchCondition {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub key: Option<Cow<'static, str>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub pattern: Option<Cow<'static, str>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub pattern_type: Option<Cow<'static, str>>,
+    pub rel_type: Cow<'static, str>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub include_fallbacks: Option<bool>,
+}
+
 /// The collection of push rules for a user.
 #[derive(Debug, Clone, Default)]
 #[pyclass(frozen)]
@@ -391,15 +407,21 @@ impl PushRules {
 pub struct FilteredPushRules {
     push_rules: PushRules,
     enabled_map: BTreeMap<String, bool>,
+    msc3664_enabled: bool,
 }
 
 #[pymethods]
 impl FilteredPushRules {
     #[new]
-    pub fn py_new(push_rules: PushRules, enabled_map: BTreeMap<String, bool>) -> Self {
+    pub fn py_new(
+        push_rules: PushRules,
+        enabled_map: BTreeMap<String, bool>,
+        msc3664_enabled: bool,
+    ) -> Self {
         Self {
             push_rules,
             enabled_map,
+            msc3664_enabled,
         }
     }
 
@@ -414,13 +436,25 @@ impl FilteredPushRules {
     /// Iterates over all the rules and their enabled state, including base
     /// rules, in the order they should be executed in.
     fn iter(&self) -> impl Iterator<Item = (&PushRule, bool)> {
-        self.push_rules.iter().map(|r| {
-            let enabled = *self
-                .enabled_map
-                .get(&*r.rule_id)
-                .unwrap_or(&r.default_enabled);
-            (r, enabled)
-        })
+        self.push_rules
+            .iter()
+            .filter(|rule| {
+                // Ignore disabled experimental push rules
+                if !self.msc3664_enabled
+                    && rule.rule_id == "global/override/.im.nheko.msc3664.reply"
+                {
+                    return false;
+                }
+
+                true
+            })
+            .map(|r| {
+                let enabled = *self
+                    .enabled_map
+                    .get(&*r.rule_id)
+                    .unwrap_or(&r.default_enabled);
+                (r, enabled)
+            })
     }
 }
 
@@ -447,6 +481,17 @@ fn test_deserialize_condition() {
 }
 
 #[test]
+fn test_deserialize_unstable_msc3664_condition() {
+    let json = r#"{"kind":"im.nheko.msc3664.related_event_match","key":"content.body","pattern":"coffee","rel_type":"m.in_reply_to"}"#;
+
+    let condition: Condition = serde_json::from_str(json).unwrap();
+    assert!(matches!(
+        condition,
+        Condition::Known(KnownCondition::RelatedEventMatch(_))
+    ));
+}
+
+#[test]
 fn test_deserialize_custom_condition() {
     let json = r#"{"kind":"custom_tag"}"#;
 
diff --git a/stubs/synapse/synapse_rust/push.pyi b/stubs/synapse/synapse_rust/push.pyi
index f2a61df660..f3b6d6c933 100644
--- a/stubs/synapse/synapse_rust/push.pyi
+++ b/stubs/synapse/synapse_rust/push.pyi
@@ -25,7 +25,9 @@ class PushRules:
     def rules(self) -> Collection[PushRule]: ...
 
 class FilteredPushRules:
-    def __init__(self, push_rules: PushRules, enabled_map: Dict[str, bool]): ...
+    def __init__(
+        self, push_rules: PushRules, enabled_map: Dict[str, bool], msc3664_enabled: bool
+    ): ...
     def rules(self) -> Collection[Tuple[PushRule, bool]]: ...
 
 def get_base_rule_ids() -> Collection[str]: ...
@@ -37,6 +39,8 @@ class PushRuleEvaluator:
         room_member_count: int,
         sender_power_level: Optional[int],
         notification_power_levels: Mapping[str, int],
+        related_events_flattened: Mapping[str, Mapping[str, str]],
+        related_event_match_enabled: bool,
     ): ...
     def run(
         self,
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 4009add01d..d9bdd66d55 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -98,6 +98,9 @@ class ExperimentalConfig(Config):
         # MSC3773: Thread notifications
         self.msc3773_enabled: bool = experimental.get("msc3773_enabled", False)
 
+        # MSC3664: Pushrules to match on related events
+        self.msc3664_enabled: bool = experimental.get("msc3664_enabled", False)
+
         # MSC3848: Introduce errcodes for specific event sending failures
         self.msc3848_enabled: bool = experimental.get("msc3848_enabled", False)
 
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index d7795a9080..75b7e126ca 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -45,7 +45,6 @@ if TYPE_CHECKING:
 
 logger = logging.getLogger(__name__)
 
-
 push_rules_invalidation_counter = Counter(
     "synapse_push_bulk_push_rule_evaluator_push_rules_invalidation_counter", ""
 )
@@ -107,6 +106,8 @@ class BulkPushRuleEvaluator:
         self.clock = hs.get_clock()
         self._event_auth_handler = hs.get_event_auth_handler()
 
+        self._related_event_match_enabled = self.hs.config.experimental.msc3664_enabled
+
         self.room_push_rule_cache_metrics = register_cache(
             "cache",
             "room_push_rule_cache",
@@ -218,6 +219,48 @@ class BulkPushRuleEvaluator:
 
         return pl_event.content if pl_event else {}, sender_level
 
+    async def _related_events(self, event: EventBase) -> Dict[str, Dict[str, str]]:
+        """Fetches the related events for 'event'. Sets the im.vector.is_falling_back key if the event is from a fallback relation
+
+        Returns:
+            Mapping of relation type to flattened events.
+        """
+        related_events: Dict[str, Dict[str, str]] = {}
+        if self._related_event_match_enabled:
+            related_event_id = event.content.get("m.relates_to", {}).get("event_id")
+            relation_type = event.content.get("m.relates_to", {}).get("rel_type")
+            if related_event_id is not None and relation_type is not None:
+                related_event = await self.store.get_event(
+                    related_event_id, allow_none=True
+                )
+                if related_event is not None:
+                    related_events[relation_type] = _flatten_dict(related_event)
+
+            reply_event_id = (
+                event.content.get("m.relates_to", {})
+                .get("m.in_reply_to", {})
+                .get("event_id")
+            )
+
+            # convert replies to pseudo relations
+            if reply_event_id is not None:
+                related_event = await self.store.get_event(
+                    reply_event_id, allow_none=True
+                )
+
+                if related_event is not None:
+                    related_events["m.in_reply_to"] = _flatten_dict(related_event)
+
+                    # indicate that this is from a fallback relation.
+                    if relation_type == "m.thread" and event.content.get(
+                        "m.relates_to", {}
+                    ).get("is_falling_back", False):
+                        related_events["m.in_reply_to"][
+                            "im.vector.is_falling_back"
+                        ] = ""
+
+        return related_events
+
     async def action_for_events_by_user(
         self, events_and_context: List[Tuple[EventBase, EventContext]]
     ) -> None:
@@ -286,6 +329,8 @@ class BulkPushRuleEvaluator:
                 # the parent is part of a thread.
                 thread_id = await self.store.get_thread_id(relation.parent_id)
 
+        related_events = await self._related_events(event)
+
         # It's possible that old room versions have non-integer power levels (floats or
         # strings). Workaround this by explicitly converting to int.
         notification_levels = power_levels.get("notifications", {})
@@ -298,6 +343,8 @@ class BulkPushRuleEvaluator:
             room_member_count,
             sender_power_level,
             notification_levels,
+            related_events,
+            self._related_event_match_enabled,
         )
 
         users = rules_by_user.keys()
diff --git a/synapse/rest/client/capabilities.py b/synapse/rest/client/capabilities.py
index 4237071c61..e84dde31b1 100644
--- a/synapse/rest/client/capabilities.py
+++ b/synapse/rest/client/capabilities.py
@@ -77,6 +77,11 @@ class CapabilitiesRestServlet(RestServlet):
                 "enabled": True,
             }
 
+        if self.config.experimental.msc3664_enabled:
+            response["capabilities"]["im.nheko.msc3664.related_event_match"] = {
+                "enabled": self.config.experimental.msc3664_enabled,
+            }
+
         return HTTPStatus.OK, response
 
 
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index 51416b2236..b6c15f29f8 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -29,6 +29,7 @@ from typing import (
 )
 
 from synapse.api.errors import StoreError
+from synapse.config.homeserver import ExperimentalConfig
 from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.database import (
@@ -62,7 +63,9 @@ logger = logging.getLogger(__name__)
 
 
 def _load_rules(
-    rawrules: List[JsonDict], enabled_map: Dict[str, bool]
+    rawrules: List[JsonDict],
+    enabled_map: Dict[str, bool],
+    experimental_config: ExperimentalConfig,
 ) -> FilteredPushRules:
     """Take the DB rows returned from the DB and convert them into a full
     `FilteredPushRules` object.
@@ -80,7 +83,9 @@ def _load_rules(
 
     push_rules = PushRules(ruleslist)
 
-    filtered_rules = FilteredPushRules(push_rules, enabled_map)
+    filtered_rules = FilteredPushRules(
+        push_rules, enabled_map, msc3664_enabled=experimental_config.msc3664_enabled
+    )
 
     return filtered_rules
 
@@ -160,7 +165,7 @@ class PushRulesWorkerStore(
 
         enabled_map = await self.get_push_rules_enabled_for_user(user_id)
 
-        return _load_rules(rows, enabled_map)
+        return _load_rules(rows, enabled_map, self.hs.config.experimental)
 
     async def get_push_rules_enabled_for_user(self, user_id: str) -> Dict[str, bool]:
         results = await self.db_pool.simple_select_list(
@@ -219,7 +224,9 @@ class PushRulesWorkerStore(
         results: Dict[str, FilteredPushRules] = {}
 
         for user_id, rules in raw_rules.items():
-            results[user_id] = _load_rules(rules, enabled_map_by_user.get(user_id, {}))
+            results[user_id] = _load_rules(
+                rules, enabled_map_by_user.get(user_id, {}), self.hs.config.experimental
+            )
 
         return results
 
diff --git a/tests/push/test_push_rule_evaluator.py b/tests/push/test_push_rule_evaluator.py
index decf619466..fe7c145840 100644
--- a/tests/push/test_push_rule_evaluator.py
+++ b/tests/push/test_push_rule_evaluator.py
@@ -38,7 +38,9 @@ from tests.test_utils.event_injection import create_event, inject_member_event
 
 
 class PushRuleEvaluatorTestCase(unittest.TestCase):
-    def _get_evaluator(self, content: JsonDict) -> PushRuleEvaluator:
+    def _get_evaluator(
+        self, content: JsonDict, related_events=None
+    ) -> PushRuleEvaluator:
         event = FrozenEvent(
             {
                 "event_id": "$event_id",
@@ -58,6 +60,8 @@ class PushRuleEvaluatorTestCase(unittest.TestCase):
             room_member_count,
             sender_power_level,
             power_levels.get("notifications", {}),
+            {} if related_events is None else related_events,
+            True,
         )
 
     def test_display_name(self) -> None:
@@ -292,6 +296,215 @@ class PushRuleEvaluatorTestCase(unittest.TestCase):
             {"sound": "default", "highlight": True},
         )
 
+    def test_related_event_match(self):
+        evaluator = self._get_evaluator(
+            {
+                "m.relates_to": {
+                    "event_id": "$parent_event_id",
+                    "key": "😀",
+                    "rel_type": "m.annotation",
+                    "m.in_reply_to": {
+                        "event_id": "$parent_event_id",
+                    },
+                }
+            },
+            {
+                "m.in_reply_to": {
+                    "event_id": "$parent_event_id",
+                    "type": "m.room.message",
+                    "sender": "@other_user:test",
+                    "room_id": "!room:test",
+                    "content.msgtype": "m.text",
+                    "content.body": "Original message",
+                },
+                "m.annotation": {
+                    "event_id": "$parent_event_id",
+                    "type": "m.room.message",
+                    "sender": "@other_user:test",
+                    "room_id": "!room:test",
+                    "content.msgtype": "m.text",
+                    "content.body": "Original message",
+                },
+            },
+        )
+        self.assertTrue(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                    "pattern": "@other_user:test",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                    "pattern": "@user:test",
+                },
+                "@other_user:test",
+                "display_name",
+            )
+        )
+        self.assertTrue(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.annotation",
+                    "pattern": "@other_user:test",
+                },
+                "@other_user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertTrue(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "rel_type": "m.in_reply_to",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "rel_type": "m.replace",
+                },
+                "@other_user:test",
+                "display_name",
+            )
+        )
+
+    def test_related_event_match_with_fallback(self):
+        evaluator = self._get_evaluator(
+            {
+                "m.relates_to": {
+                    "event_id": "$parent_event_id",
+                    "key": "😀",
+                    "rel_type": "m.thread",
+                    "is_falling_back": True,
+                    "m.in_reply_to": {
+                        "event_id": "$parent_event_id",
+                    },
+                }
+            },
+            {
+                "m.in_reply_to": {
+                    "event_id": "$parent_event_id",
+                    "type": "m.room.message",
+                    "sender": "@other_user:test",
+                    "room_id": "!room:test",
+                    "content.msgtype": "m.text",
+                    "content.body": "Original message",
+                    "im.vector.is_falling_back": "",
+                },
+                "m.thread": {
+                    "event_id": "$parent_event_id",
+                    "type": "m.room.message",
+                    "sender": "@other_user:test",
+                    "room_id": "!room:test",
+                    "content.msgtype": "m.text",
+                    "content.body": "Original message",
+                },
+            },
+        )
+        self.assertTrue(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                    "pattern": "@other_user:test",
+                    "include_fallbacks": True,
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                    "pattern": "@other_user:test",
+                    "include_fallbacks": False,
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                    "pattern": "@other_user:test",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+
+    def test_related_event_match_no_related_event(self):
+        evaluator = self._get_evaluator(
+            {"msgtype": "m.text", "body": "Message without related event"}
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                    "pattern": "@other_user:test",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "key": "sender",
+                    "rel_type": "m.in_reply_to",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+        self.assertFalse(
+            evaluator.matches(
+                {
+                    "kind": "im.nheko.msc3664.related_event_match",
+                    "rel_type": "m.in_reply_to",
+                },
+                "@user:test",
+                "display_name",
+            )
+        )
+
 
 class TestBulkPushRuleEvaluator(unittest.HomeserverTestCase):
     """Tests for the bulk push rule evaluator"""