FEATURE: Reset bump date when deleting a post (#33747)

Necro-posting by spammers will bump the topic, and once you delete them,
those topics will still sit in `/latest` without any benifit.

This commit implements automatic resetting of topic bump date when a
post is deleted, so the topic will go to the correct place it belongs on
`/latest` based on its last public post.

app/models/post.rb

@@ -554,6 +554,10 @@ class Post < ActiveRecord::Base
     post_number.blank? ? topic.try(:highest_post_number) == 0 : post_number == 1
   end
 
+  def is_last_reply?
+    topic.try(:highest_post_number) == post_number && post_number != 1
+  end
+
   def is_category_description?
     topic.present? && topic.is_category_topic? && is_first_post?
   end

lib/post_destroyer.rb

@@ -75,6 +75,8 @@ class PostDestroyer
     delete_removed_posts_after =
       @opts[:delete_removed_posts_after] || SiteSetting.delete_removed_posts_after
 
+    should_reset_bumped_at = @post.is_last_reply? && !@post.whisper?
+
     if delete_removed_posts_after < 1 || post_is_reviewable? ||
          Guardian.new(@user).can_moderate_topic?(@topic) || permanent?
       perform_delete
@@ -105,6 +107,8 @@ class PostDestroyer
         Discourse.clear_urls!
       end
     end
+
+    @topic.reset_bumped_at if should_reset_bumped_at
   end
 
   def recover

spec/lib/post_destroyer_spec.rb

@@ -1278,4 +1278,46 @@ RSpec.describe PostDestroyer do
       end
     end
   end
+
+  describe "deleting a last reply" do
+    let!(:topic) { post.topic }
+    let!(:second_last_reply) do
+      freeze_time 1.day.from_now
+      create_post(topic:, user: coding_horror)
+    end
+    fab!(:user)
+    let!(:last_reply) do
+      freeze_time 2.days.from_now
+      create_post(topic:, user:)
+    end
+
+    context "when deleting by the creator" do
+      before { PostDestroyer.new(user, last_reply).destroy }
+
+      it "will reset the topic's bumped_at" do
+        topic.reload
+
+        expect(topic.bumped_at).to eq_time(second_last_reply.created_at)
+      end
+
+      it "still can see the post" do
+        last_reply.reload
+
+        expect(last_reply.deleted_at).to be_blank
+        expect(last_reply.deleted_by).to be_blank
+        expect(last_reply.user_deleted).to eq(true)
+        expect(last_reply.raw).to eq(I18n.t("js.post.deleted_by_author_simple"))
+      end
+    end
+
+    context "when deleting by a staff user" do
+      before { PostDestroyer.new(moderator, last_reply).destroy }
+
+      it "will reset the topic's bumped_at" do
+        topic.reload
+
+        expect(topic.bumped_at).to eq_time(second_last_reply.created_at)
+      end
+    end
+  end
 end