Create MSC1767 (extensible events) room version; Implement MSC3932 (#14521)

* Add MSC1767's dedicated room version, based on v10

* Only enable MSC1767 room version if the config flag is on

Using a similar technique to knocking:
https://github.com/matrix-org/synapse/pull/6739/files#diff-3af529eedb0e00279bafb7369370c9654b37792af8eafa0925400e9281d57f0a

* Support MSC3932: Extensible events room version feature flag

* Changelog entry

4 files changed, 130 insertions, 2 deletions

diff --git a/changelog.d/14521.feature b/changelog.d/14521.feature
new file mode 100644
index 0000000000..210acaa8ee
--- /dev/null
+++ b/changelog.d/14521.feature
@@ -0,0 +1 @@
+Add unstable support for an Extensible Events room version (`org.matrix.msc1767.10`) via [MSC1767](https://github.com/matrix-org/matrix-spec-proposals/pull/1767), [MSC3931](https://github.com/matrix-org/matrix-spec-proposals/pull/3931), [MSC3932](https://github.com/matrix-org/matrix-spec-proposals/pull/3932), and [MSC3933](https://github.com/matrix-org/matrix-spec-proposals/pull/3933).
\ No newline at end of file
diff --git a/rust/src/push/evaluator.rs b/rust/src/push/evaluator.rs
index e8e3d604ee..b4c3039aba 100644
--- a/rust/src/push/evaluator.rs
+++ b/rust/src/push/evaluator.rs
@@ -12,8 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::borrow::Cow;
 use std::collections::BTreeMap;
 
+use crate::push::{PushRule, PushRules};
 use anyhow::{Context, Error};
 use lazy_static::lazy_static;
 use log::warn;
@@ -32,7 +34,30 @@ lazy_static! {
 
     /// Used to determine which MSC3931 room version feature flags are actually known to
     /// the push evaluator.
-    static ref KNOWN_RVER_FLAGS: Vec<String> = vec![];
+    static ref KNOWN_RVER_FLAGS: Vec<String> = vec![
+        RoomVersionFeatures::ExtensibleEvents.as_str().to_string(),
+    ];
+
+    /// The "safe" rule IDs which are not affected by MSC3932's behaviour (room versions which
+    /// declare Extensible Events support ultimately *disable* push rules which do not declare
+    /// *any* MSC3931 room_version_supports condition).
+    static ref SAFE_EXTENSIBLE_EVENTS_RULE_IDS: Vec<String> = vec![
+        "global/override/.m.rule.master".to_string(),
+        "global/override/.m.rule.roomnotif".to_string(),
+        "global/content/.m.rule.contains_user_name".to_string(),
+    ];
+}
+
+enum RoomVersionFeatures {
+    ExtensibleEvents,
+}
+
+impl RoomVersionFeatures {
+    fn as_str(&self) -> &'static str {
+        match self {
+            RoomVersionFeatures::ExtensibleEvents => "org.matrix.msc3932.extensible_events",
+        }
+    }
 }
 
 /// Allows running a set of push rules against a particular event.
@@ -121,7 +146,22 @@ impl PushRuleEvaluator {
                 continue;
             }
 
+            let rule_id = &push_rule.rule_id().to_string();
+            let extev_flag = &RoomVersionFeatures::ExtensibleEvents.as_str().to_string();
+            let supports_extensible_events = self.room_version_feature_flags.contains(extev_flag);
+            let safe_from_rver_condition = SAFE_EXTENSIBLE_EVENTS_RULE_IDS.contains(rule_id);
+            let mut has_rver_condition = false;
+
             for condition in push_rule.conditions.iter() {
+                has_rver_condition = has_rver_condition
+                    || match condition {
+                        Condition::Known(known) => match known {
+                            // per MSC3932, we just need *any* room version condition to match
+                            KnownCondition::RoomVersionSupports { feature: _ } => true,
+                            _ => false,
+                        },
+                        _ => false,
+                    };
                 match self.match_condition(condition, user_id, display_name) {
                     Ok(true) => {}
                     Ok(false) => continue 'outer,
@@ -132,6 +172,13 @@ impl PushRuleEvaluator {
                 }
             }
 
+            // MSC3932: Disable push rules in extensible event-supporting room versions if they
+            // don't describe *any* MSC3931 room version condition, unless the rule is on the
+            // safe list.
+            if !has_rver_condition && !safe_from_rver_condition && supports_extensible_events {
+                continue;
+            }
+
             let actions = push_rule
                 .actions
                 .iter()
@@ -394,3 +441,51 @@ fn push_rule_evaluator() {
     let result = evaluator.run(&FilteredPushRules::default(), None, Some("bob"));
     assert_eq!(result.len(), 3);
 }
+
+#[test]
+fn test_requires_room_version_supports_condition() {
+    let mut flattened_keys = BTreeMap::new();
+    flattened_keys.insert("content.body".to_string(), "foo bar bob hello".to_string());
+    let flags = vec![RoomVersionFeatures::ExtensibleEvents.as_str().to_string()];
+    let evaluator = PushRuleEvaluator::py_new(
+        flattened_keys,
+        10,
+        Some(0),
+        BTreeMap::new(),
+        BTreeMap::new(),
+        false,
+        flags,
+        true,
+    )
+    .unwrap();
+
+    // first test: are the master and contains_user_name rules excluded from the "requires room
+    // version condition" check?
+    let mut result = evaluator.run(
+        &FilteredPushRules::default(),
+        Some("@bob:example.org"),
+        None,
+    );
+    assert_eq!(result.len(), 3);
+
+    // second test: if an appropriate push rule is in play, does it get handled?
+    let custom_rule = PushRule {
+        rule_id: Cow::from("global/underride/.org.example.extensible"),
+        priority_class: 1, // underride
+        conditions: Cow::from(vec![Condition::Known(
+            KnownCondition::RoomVersionSupports {
+                feature: Cow::from(RoomVersionFeatures::ExtensibleEvents.as_str().to_string()),
+            },
+        )]),
+        actions: Cow::from(vec![Action::Notify]),
+        default: false,
+        default_enabled: true,
+    };
+    let rules = PushRules::new(vec![custom_rule]);
+    result = evaluator.run(
+        &FilteredPushRules::py_new(rules, BTreeMap::new(), true),
+        None,
+        None,
+    );
+    assert_eq!(result.len(), 1);
+}
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index 1bd1ef3e2b..ac62011c9f 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -51,6 +51,13 @@ class RoomDisposition:
     UNSTABLE = "unstable"
 
 
+class PushRuleRoomFlag:
+    """Enum for listing possible MSC3931 room version feature flags, for push rules"""
+
+    # MSC3932: Room version supports MSC1767 Extensible Events.
+    EXTENSIBLE_EVENTS = "org.matrix.msc3932.extensible_events"
+
+
 @attr.s(slots=True, frozen=True, auto_attribs=True)
 class RoomVersion:
     """An object which describes the unique attributes of a room version."""
@@ -96,7 +103,7 @@ class RoomVersion:
     # is not enough to mark it "supported": the push rule evaluator also needs to
     # support the flag. Unknown flags are ignored by the evaluator, making conditions
     # fail if used.
-    msc3931_push_features: List[str]
+    msc3931_push_features: List[str]  # values from PushRuleRoomFlag
 
 
 class RoomVersions:
@@ -347,6 +354,26 @@ class RoomVersions:
         msc3667_int_only_power_levels=False,
         msc3931_push_features=[],
     )
+    MSC1767v10 = RoomVersion(
+        # MSC1767 (Extensible Events) based on room version "10"
+        "org.matrix.msc1767.10",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.ROOM_V4_PLUS,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        msc2176_redaction_rules=False,
+        msc3083_join_rules=True,
+        msc3375_redaction_rules=True,
+        msc2403_knocking=True,
+        msc2716_historical=False,
+        msc2716_redactions=False,
+        msc3787_knock_restricted_join_rule=True,
+        msc3667_int_only_power_levels=True,
+        msc3931_push_features=[PushRuleRoomFlag.EXTENSIBLE_EVENTS],
+    )
 
 
 KNOWN_ROOM_VERSIONS: Dict[str, RoomVersion] = {
diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index b3f51fc57d..573fa0386f 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -16,6 +16,7 @@ from typing import Any, Optional
 
 import attr
 
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersions
 from synapse.config._base import Config
 from synapse.types import JsonDict
 
@@ -131,3 +132,7 @@ class ExperimentalConfig(Config):
 
         # MSC1767 and friends: Extensible Events
         self.msc1767_enabled: bool = experimental.get("msc1767_enabled", False)
+        if self.msc1767_enabled:
+            # Enable room version (and thus applicable push rules from MSC3931/3932)
+            version_id = RoomVersions.MSC1767v10.identifier
+            KNOWN_ROOM_VERSIONS[version_id] = RoomVersions.MSC1767v10