FIX: Use hashtags in channel archive PMs if available (#19859)

If the enable_experimental_hashtag_autocomplete setting is
enabled, then we should autolink hashtag references to the
archived channels (e.g. #blah::channel) for a nicer UX, and
just show the channel name if not (since doing #channelName
can lead to weird inconsistent results).

plugins/chat/config/locales/server.en.yml

@@ -29,17 +29,17 @@ en:
       title: "Chat Channel Archive Complete"
       subject_template: "Chat channel archive completed successfully"
       text_body_template: |
-        Archiving the chat channel **\#%{channel_name}** has been completed successfully. The messages were copied into the topic [%{topic_title}](%{topic_url}).
+        Archiving the chat channel %{channel_hashtag_or_name} has been completed successfully. The messages were copied into the topic [%{topic_title}](%{topic_url}).
     chat_channel_archive_failed:
       title: "Chat Channel Archive Failed"
       subject_template: "Chat channel archive failed"
       text_body_template: |
-        Archiving the chat channel **\#%{channel_name}** has failed. %{messages_archived} messages have been archived. Partially archived messages were copied into the topic [%{topic_title}](%{topic_url}). Visit the channel at %{channel_url} to retry.
+        Archiving the chat channel %{channel_hashtag_or_name} has failed. %{messages_archived} messages have been archived. Partially archived messages were copied into the topic [%{topic_title}](%{topic_url}). Visit the channel at %{channel_url} to retry.
     chat_channel_archive_failed_no_topic:
       title: "Chat Channel Archive Failed"
       subject_template: "Chat channel archive failed"
       text_body_template: |
-        Archiving the chat channel **\#%{channel_name}** has failed. No messages have been archived. The topic was not created successfully for the following reasons:
+        Archiving the chat channel %{channel_hashtag_or_name} has failed. No messages have been archived. The topic was not created successfully for the following reasons:
 
           %{topic_validation_errors}
 

plugins/chat/lib/chat_channel_archive_service.rb

@@ -248,7 +248,7 @@ class Chat::ChatChannelArchiveService
 
   def notify_archiver(result, error_message: nil)
     base_translation_params = {
-      channel_name: chat_channel_title,
+      channel_hashtag_or_name: channel_hashtag_or_name,
       topic_title: chat_channel_archive.destination_topic&.title,
       topic_url: chat_channel_archive.destination_topic&.url,
       topic_validation_errors: result == :failed_no_topic ? error_message : nil,
@@ -301,4 +301,11 @@ class Chat::ChatChannelArchiveService
   def kick_all_users
     Chat::ChatChannelMembershipManager.new(chat_channel).unfollow_all_users
   end
+
+  def channel_hashtag_or_name
+    if chat_channel.slug.present? && SiteSetting.enable_experimental_hashtag_autocomplete
+      return "##{chat_channel.slug}::channel"
+    end
+    chat_channel_title
+  end
 end

plugins/chat/spec/lib/chat_channel_archive_service_spec.rb

@@ -12,6 +12,8 @@ describe Chat::ChatChannelArchiveService do
   let(:topic_params) { { topic_title: "This will be a new topic", category_id: category.id } }
   subject { Chat::ChatChannelArchiveService }
 
+  before { SiteSetting.chat_enabled = true }
+
   describe "#create_archive_process" do
     before { 3.times { Fabricate(:chat_message, chat_channel: channel) } }
 
@@ -184,6 +186,20 @@ describe Chat::ChatChannelArchiveService do
         expect(pm_topic.first_post.raw).to include("Title can't have more than 1 emoji")
       end
 
+      context "when enable_experimental_hashtag_autocomplete" do
+        before { SiteSetting.enable_experimental_hashtag_autocomplete = true }
+
+        it "uses the channel slug to autolink a hashtag for the channel in the PM" do
+          create_messages(3) && start_archive
+          subject.new(@channel_archive).execute
+          expect(@channel_archive.reload.complete?).to eq(true)
+          pm_topic = Topic.private_messages.last
+          expect(pm_topic.first_post.cooked).to include(
+            "<a class=\"hashtag-cooked\" href=\"#{channel.relative_url}\" data-type=\"channel\" data-slug=\"#{channel.slug}\" data-ref=\"#{channel.slug}::channel\"><svg class=\"fa d-icon d-icon-comment svg-icon svg-node\"><use href=\"#comment\"></use></svg><span>#{channel.title(user)}</span></a>",
+          )
+        end
+      end
+
       describe "channel members" do
         before do
           create_messages(3)