api: Add ZulipStream.topicsPolicy

Enum TopicsPolicy is created for these four values: inherit,
allow_empty_topic, disable_empty_topic, and empty_topic_only.

Author: chungwwei

lib/api/model/events.dart

@@ -681,6 +681,8 @@ class ChannelUpdateEvent extends ChannelEvent {
         return value as bool;
       case ChannelPropertyName.messageRetentionDays:
         return value as int?;
+      case ChannelPropertyName.topicsPolicy:
+        return TopicsPolicy.fromRawString(value as String);
       case ChannelPropertyName.channelPostPolicy:
         return ChannelPostPolicy.fromApiValue(value as int);
       case ChannelPropertyName.folderId:

lib/api/model/events.g.dart

@@ -659,6 +659,8 @@ class ZulipStream {
   bool isWebPublic; // present since 2.1, according to /api/changelog
   bool historyPublicToSubscribers;
   int? messageRetentionDays;
+  @JsonKey(defaultValue: TopicsPolicy.inherit)
+  TopicsPolicy topicsPolicy;
   @JsonKey(name: 'stream_post_policy')
   ChannelPostPolicy? channelPostPolicy; // TODO(server-10) remove
   // final bool isAnnouncementOnly; // deprecated for `channelPostPolicy`; ignore
@@ -684,6 +686,7 @@ class ZulipStream {
     required this.isWebPublic,
     required this.historyPublicToSubscribers,
     required this.messageRetentionDays,
+    required this.topicsPolicy,
     required this.channelPostPolicy,
     required this.folderId,
     required this.canAddSubscribersGroup,
@@ -708,6 +711,7 @@ class ZulipStream {
       isWebPublic: subscription.isWebPublic,
       historyPublicToSubscribers: subscription.historyPublicToSubscribers,
       messageRetentionDays: subscription.messageRetentionDays,
+      topicsPolicy: subscription.topicsPolicy,
       channelPostPolicy: subscription.channelPostPolicy,
       folderId: subscription.folderId,
       canAddSubscribersGroup: subscription.canAddSubscribersGroup,
@@ -744,6 +748,8 @@ enum ChannelPropertyName {
   // isWebPublic is updated via its own [ChannelUpdateEvent] field
   // historyPublicToSubscribers is updated via its own [ChannelUpdateEvent] field
   messageRetentionDays,
+  @JsonValue('topics_policy')
+  topicsPolicy,
   @JsonValue('stream_post_policy')
   channelPostPolicy,
   folderId,
@@ -765,6 +771,24 @@ enum ChannelPropertyName {
     .map((key, value) => MapEntry(value, key));
 }
 
+/// A value of [ZulipStream.topicsPolicy].
+///
+/// For docs, search for "topics_policy"
+/// in <https://zulip.com/api/get-stream-by-id>.
+@JsonEnum(fieldRename: FieldRename.snake)
+enum TopicsPolicy {
+  inherit,
+  allowEmptyTopic,
+  disableEmptyTopic,
+  emptyTopicOnly;
+
+  static TopicsPolicy fromRawString(String raw) => _byRawString[raw] ?? inherit;
+
+  static final _byRawString = _$TopicsPolicyEnumMap.map((key, value) => MapEntry(value, key));
+
+  String toJson() => _$TopicsPolicyEnumMap[this]!;
+}
+
 /// Policy for which users can post to the stream.
 ///
 /// For docs, search for "stream_post_policy"
@@ -830,6 +854,7 @@ class Subscription extends ZulipStream {
     required super.isWebPublic,
     required super.historyPublicToSubscribers,
     required super.messageRetentionDays,
+    required super.topicsPolicy,
     required super.channelPostPolicy,
     required super.folderId,
     required super.canAddSubscribersGroup,

lib/api/model/model.dart

@@ -444,6 +444,8 @@ class ChannelStoreImpl extends HasUserStore with ChannelStore {
             stream.inviteOnly = event.value as bool;
           case ChannelPropertyName.messageRetentionDays:
             stream.messageRetentionDays = event.value as int?;
+          case ChannelPropertyName.topicsPolicy:
+            stream.topicsPolicy = event.value as TopicsPolicy;
           case ChannelPropertyName.channelPostPolicy:
             stream.channelPostPolicy = event.value as ChannelPostPolicy;
           case ChannelPropertyName.folderId:

lib/api/model/model.g.dart

@@ -464,6 +464,7 @@ ZulipStream stream({
   bool? isWebPublic,
   bool? historyPublicToSubscribers,
   int? messageRetentionDays,
+  TopicsPolicy? topicsPolicy,
   ChannelPostPolicy? channelPostPolicy,
   int? folderId,
   GroupSettingValue? canAddSubscribersGroup,
@@ -496,6 +497,7 @@ ZulipStream stream({
     isWebPublic: isWebPublic ?? false,
     historyPublicToSubscribers: historyPublicToSubscribers ?? true,
     messageRetentionDays: messageRetentionDays,
+    topicsPolicy: topicsPolicy ?? TopicsPolicy.inherit,
     channelPostPolicy: channelPostPolicy ?? ChannelPostPolicy.any,
     folderId: folderId,
     canAddSubscribersGroup: canAddSubscribersGroup ?? GroupSettingValueNamed(nobodyGroup.id),
@@ -541,6 +543,7 @@ Subscription subscription(
     isWebPublic: stream.isWebPublic,
     historyPublicToSubscribers: stream.historyPublicToSubscribers,
     messageRetentionDays: stream.messageRetentionDays,
+    topicsPolicy: stream.topicsPolicy,
     channelPostPolicy: stream.channelPostPolicy,
     folderId: stream.folderId,
     canAddSubscribersGroup: stream.canAddSubscribersGroup,
@@ -1261,6 +1264,8 @@ ChannelUpdateEvent channelUpdateEvent(
       assert(value is bool);
     case ChannelPropertyName.messageRetentionDays:
       assert(value is int?);
+    case ChannelPropertyName.topicsPolicy:
+      assert(value is TopicsPolicy);
     case ChannelPropertyName.channelPostPolicy:
       assert(value is ChannelPostPolicy);
     case ChannelPropertyName.folderId: