Bring back conversation.leaveGroup for GV1 scenarios

ts/models/conversations.ts

@@ -2793,6 +2793,43 @@ export class ConversationModel extends window.Backbone.Model<
     }
   }
 
+  async leaveGroup(): Promise<void> {
+    const now = Date.now();
+    if (this.get('type') === 'group') {
+      const groupIdentifiers = this.getRecipients();
+      this.set({ left: true });
+      window.Signal.Data.updateConversation(this.attributes);
+
+      const model = new Whisper.Message(({
+        group_update: { left: 'You' },
+        conversationId: this.id,
+        type: 'outgoing',
+        sent_at: now,
+        received_at: now,
+        // TODO: DESKTOP-722
+      } as unknown) as MessageAttributesType);
+
+      const id = await window.Signal.Data.saveMessage(model.attributes, {
+        Message: Whisper.Message,
+      });
+      model.set({ id });
+
+      const message = window.MessageController.register(model.id, model);
+      this.addSingleMessage(message);
+
+      const options = this.getSendOptions();
+      message.send(
+        this.wrapSend(
+          window.textsecure.messaging.leaveGroup(
+            this.id,
+            groupIdentifiers,
+            options
+          )
+        )
+      );
+    }
+  }
+
   async markRead(
     newestUnreadDate: number,
     providedOptions: { readAt?: number; sendReadReceipts: boolean }

ts/textsecure/SendMessage.ts

@@ -1372,9 +1372,7 @@ export default class MessageSender {
     proto: DataMessageClass,
     timestamp = Date.now(),
     options = {}
-  ): Promise<
-    CallbackResultType | Omit<CallbackResultType, 'discoveredIdentifierPairs'>
-  > {
+  ): Promise<CallbackResultType> {
     const myE164 = window.textsecure.storage.user.getNumber();
     const myUuid = window.textsecure.storage.user.getUuid();
     const identifiers = providedIdentifiers.filter(
@@ -1383,11 +1381,12 @@ export default class MessageSender {
 
     if (identifiers.length === 0) {
       return Promise.resolve({
-        successfulIdentifiers: [],
-        failoverIdentifiers: [],
-        errors: [],
-        unidentifiedDeliveries: [],
         dataMessage: proto.toArrayBuffer(),
+        discoveredIdentifierPairs: [],
+        errors: [],
+        failoverIdentifiers: [],
+        successfulIdentifiers: [],
+        unidentifiedDeliveries: [],
       });
     }
 
@@ -1686,6 +1685,18 @@ export default class MessageSender {
     return this.server.modifyGroup(changes, options);
   }
 
+  async leaveGroup(
+    groupId: string,
+    groupIdentifiers: Array<string>,
+    options?: SendOptionsType
+  ): Promise<CallbackResultType> {
+    const proto = new window.textsecure.protobuf.DataMessage();
+    proto.group = new window.textsecure.protobuf.GroupContext();
+    proto.group.id = stringToArrayBuffer(groupId);
+    proto.group.type = window.textsecure.protobuf.GroupContext.Type.QUIT;
+    return this.sendGroupProto(groupIdentifiers, proto, Date.now(), options);
+  }
+
   async sendExpirationTimerUpdateToGroup(
     groupId: string,
     groupIdentifiers: Array<string>,