api: Add user_settings/update events, with a test for exhaustiveness

It's been tricky to find a way to verify that the event-handling
code keeps up with the settings we add in [UserSettings], the data
class we use in the initial snapshot. See #261 for some alternatives
we considered.

But at least this solution works, with type-checking of the event at
the edge, and a mechanism to ensure that all user settings we store
in our initial snapshot get updated by the user_settings/update
event.

lib/api/model/events.dart

@@ -1,5 +1,6 @@
 import 'package:json_annotation/json_annotation.dart';
 
+import 'initial_snapshot.dart';
 import 'model.dart';
 
 part 'events.g.dart';
@@ -16,6 +17,11 @@ sealed class Event {
   factory Event.fromJson(Map<String, dynamic> json) {
     switch (json['type'] as String) {
       case 'alert_words': return AlertWordsEvent.fromJson(json);
+      case 'user_settings':
+        switch (json['op'] as String) {
+          case 'update': return UserSettingsUpdateEvent.fromJson(json);
+          default: return UnexpectedEvent.fromJson(json);
+        }
       case 'realm_user':
         switch (json['op'] as String) {
           case 'add': return RealmUserAddEvent.fromJson(json);
@@ -74,6 +80,53 @@ class AlertWordsEvent extends Event {
   Map<String, dynamic> toJson() => _$AlertWordsEventToJson(this);
 }
 
+/// A Zulip event of type `user_settings` with op `update`.
+@JsonSerializable(fieldRename: FieldRename.snake)
+class UserSettingsUpdateEvent extends Event {
+  @override
+  @JsonKey(includeToJson: true)
+  String get type => 'user_settings';
+
+  @JsonKey(includeToJson: true)
+  String get op => 'update';
+
+  /// The name of the setting, or null if we don't recognize it.
+  @JsonKey(unknownEnumValue: JsonKey.nullForUndefinedEnumValue)
+  final UserSettingName? property;
+
+  /// The new value, or null if we don't recognize the setting.
+  ///
+  /// This will have the type appropriate for [property]; for example,
+  /// if the setting is boolean, then `value is bool` will always be true.
+  /// This invariant is enforced by [UserSettingsUpdateEvent.fromJson].
+  @JsonKey(readValue: _readValue)
+  final Object? value;
+
+  /// [value], with a check that its type corresponds to [property]
+  /// (e.g., `value as bool`).
+  static Object? _readValue(Map json, String key) {
+    final value = json['value'];
+    switch (UserSettingName.fromRawString(json['property'] as String)) {
+      case UserSettingName.displayEmojiReactionUsers:
+        return value as bool;
+      case null:
+        return null;
+    }
+  }
+
+  UserSettingsUpdateEvent({
+    required super.id,
+    required this.property,
+    required this.value,
+  });
+
+  factory UserSettingsUpdateEvent.fromJson(Map<String, dynamic> json) =>
+    _$UserSettingsUpdateEventFromJson(json);
+
+  @override
+  Map<String, dynamic> toJson() => _$UserSettingsUpdateEventToJson(this);
+}
+
 /// A Zulip event of type `realm_user`.
 ///
 /// The corresponding API docs are in several places for

lib/api/model/initial_snapshot.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/foundation.dart';
 import 'package:json_annotation/json_annotation.dart';
 
 import 'model.dart';
@@ -116,11 +117,14 @@ class RecentDmConversation {
 ///
 /// For docs, search for "user_settings:"
 /// in <https://zulip.com/api/register-queue>.
-@JsonSerializable(fieldRename: FieldRename.snake)
+@JsonSerializable(fieldRename: FieldRename.snake, createFieldMap: true)
 class UserSettings {
-  final bool? displayEmojiReactionUsers; // TODO(server-6)
+  bool? displayEmojiReactionUsers; // TODO(server-6)
 
-  // TODO more, as needed
+  // TODO more, as needed. When adding a setting here, please also:
+  // (1) add it to the [UserSettingName] enum below
+  // (2) then re-run the command to refresh the .g.dart files
+  // (3) handle the event that signals an update to the setting
 
   UserSettings({
     required this.displayEmojiReactionUsers,
@@ -130,4 +134,29 @@ class UserSettings {
     _$UserSettingsFromJson(json);
 
   Map<String, dynamic> toJson() => _$UserSettingsToJson(this);
+
+  /// A list of [UserSettings]'s properties, as strings.
+  // _$…FieldMap is thanks to `createFieldMap: true`
+  @visibleForTesting
+  static final Iterable<String> debugKnownNames = _$UserSettingsFieldMap.keys;
+}
+
+/// The name of a user setting that has a property in [UserSettings].
+///
+/// In Zulip event-handling code (for [UserSettingsUpdateEvent]),
+/// we switch exhaustively on a value of this type
+/// to ensure that every setting in [UserSettings] responds to the event.
+@JsonEnum(fieldRename: FieldRename.snake, alwaysCreate: true)
+enum UserSettingName {
+  displayEmojiReactionUsers;
+
+  /// Get a [UserSettingName] from a raw, snake-case string we recognize, else null.
+  ///
+  /// Example:
+  ///   'display_emoji_reaction_users' -> UserSettingName.displayEmojiReactionUsers
+  static UserSettingName? fromRawString(String raw) => _byRawString[raw];
+
+  // _$…EnumMap is thanks to `alwaysCreate: true` and `fieldRename: FieldRename.snake`
+  static final _byRawString = _$UserSettingNameEnumMap
+    .map((key, value) => MapEntry(value, key));
 }

lib/model/store.dart

@@ -174,7 +174,7 @@ class PerAccountStore extends ChangeNotifier {
   final int maxFileUploadSizeMib; // No event for this.
 
   // Data attached to the self-account on the realm.
-  final UserSettings? userSettings; // TODO(#135) update with user_settings/update event
+  final UserSettings? userSettings; // TODO(server-5)
 
   // Users and data about them.
   final Map<int, User> users;
@@ -219,6 +219,17 @@ class PerAccountStore extends ChangeNotifier {
     } else if (event is AlertWordsEvent) {
       assert(debugLog("server event: alert_words"));
       // We don't yet store this data, so there's nothing to update.
+    } else if (event is UserSettingsUpdateEvent) {
+      assert(debugLog("server event: user_settings/update ${event.property?.name ?? '[unrecognized]'}"));
+      if (event.property == null) {
+        // unrecognized setting; do nothing
+        return;
+      }
+      switch (event.property!) {
+        case UserSettingName.displayEmojiReactionUsers:
+          userSettings?.displayEmojiReactionUsers = event.value as bool;
+      }
+      notifyListeners();
     } else if (event is RealmUserAddEvent) {
       assert(debugLog("server event: realm_user/add"));
       users[event.person.userId] = event.person;

test/api/model/events_test.dart

@@ -1,6 +1,7 @@
 import 'package:checks/checks.dart';
 import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/events.dart';
+import 'package:zulip/api/model/initial_snapshot.dart';
 
 import '../../example_data.dart' as eg;
 import '../../stdlib_checks.dart';
@@ -20,4 +21,24 @@ void main() {
     check(mkEvent([])).message.flags.deepEquals([]);
     check(mkEvent(['read'])).message.flags.deepEquals(['read']);
   });
+
+  test('user_settings: all known settings have event handling', () {
+    final dataClassFieldNames = UserSettings.debugKnownNames;
+    final enumNames = UserSettingName.values.map((n) => n.name);
+    final missingEnumNames = dataClassFieldNames.where((key) => !enumNames.contains(key)).toList();
+    check(
+      missingEnumNames,
+      because:
+        'You have added these fields to [UserSettings]\n'
+        'without handling the corresponding forms of the\n'
+        'user_settings/update event in [PerAccountStore]:\n'
+        '  $missingEnumNames\n'
+        'To do that, please follow these steps:\n'
+        '  (1) Add corresponding members to the [UserSettingName] enum.\n'
+        '  (2) Then, re-run the command to refresh the .g.dart files.\n'
+        '  (3) Resolve the Dart analysis errors about not exhaustively\n'
+        '      matching on that enum, by adding new `switch` cases\n'
+        '      on the pattern of the existing cases.'
+    ).isEmpty();
+  });
 }