PERF: sends publish_new_channel only when not followed (#21755)

plugins/chat/app/controllers/chat/chat_controller.rb

@@ -125,13 +125,14 @@ module Chat
         user_ids_allowing_communication =
           UserCommScreener.new(
             acting_user: current_user,
-            target_user_ids: @chat_channel.user_chat_channel_memberships.pluck(:user_id),
+            target_user_ids:
+              @chat_channel.user_chat_channel_memberships.where(following: false).pluck(:user_id),
           ).allowing_actor_communication
 
         if user_ids_allowing_communication.any?
           Chat::Publisher.publish_new_channel(
             @chat_channel,
-            @chat_channel.chatable.users.where(id: user_ids_allowing_communication),
+            User.where(id: user_ids_allowing_communication),
           )
 
           @chat_channel

plugins/chat/spec/requests/chat_controller_spec.rb

@@ -514,6 +514,14 @@ RSpec.describe Chat::ChatController do
         expect(Chat::UserChatChannelMembership.find_by(user_id: user2.id).following).to be true
       end
 
+      it "doesn’t call publish new channel when already following" do
+        Chat::Publisher.expects(:publish_new_channel).never
+
+        sign_in(user1)
+
+        post "/chat/#{direct_message_channel.id}.json", params: { message: message }
+      end
+
       it "errors when the user is not part of the direct message channel" do
         Chat::DirectMessageUser.find_by(user: user1, direct_message: chatable).destroy!
         sign_in(user1)

plugins/chat/spec/system/unfollow_dm_channel_spec.rb

@@ -6,7 +6,7 @@ RSpec.describe "Unfollow dm channel", type: :system, js: true do
   fab!(:dm_channel_1) { Fabricate(:direct_message_channel, users: [current_user, other_user]) }
 
   let!(:chat_page) { PageObjects::Pages::Chat.new }
-  let!(:chat_channel_page) { PageObjects::Pages::ChatChannel.new }
+  let!(:channel_page) { PageObjects::Pages::ChatChannel.new }
 
   before do
     SiteSetting.navigation_menu = "sidebar"
@@ -26,8 +26,8 @@ RSpec.describe "Unfollow dm channel", type: :system, js: true do
         text = "this is fine"
         sign_in(other_user)
         chat_page.visit_channel(dm_channel_1)
-        chat_channel_page.send_message(text)
-        expect(chat_channel_page).to have_message(text: text)
+        channel_page.send_message(text)
+        expect(channel_page).to have_message(text: text)
         session.quit
       end