FIX: Consistently notify lowest post number if post_moved notification generation (#30448)

We currently query the posts table without an order when notifying users of moved posts. Generally the query will return the lowest post number post (b/c ID correlates with post_number in most cases) but not always. This adds an order to the post query in notify_moved_posts job.

Also I removed some if statement nesting with early returns / guard clauses.

app/jobs/regular/notify_moved_posts.rb

@@ -6,18 +6,21 @@ module Jobs
       raise Discourse::InvalidParameters.new(:post_ids) if args[:post_ids].blank?
       raise Discourse::InvalidParameters.new(:moved_by_id) if args[:moved_by_id].blank?
 
-      # Make sure we don't notify the same user twice (in case multiple posts were moved at once.)
-      users_notified = Set.new
       posts =
         Post
+          .includes(:user, :topic)
           .where(id: args[:post_ids])
           .where("user_id <> ?", args[:moved_by_id])
-          .includes(:user, :topic)
+          .order(post_number: :asc)
-      if posts.present?
+      return if posts.blank?
+
       moved_by = User.find_by(id: args[:moved_by_id])
 
+      # Make sure we don't notify the same user twice (in case multiple posts were moved at once.)
+      users_notified = Set.new
       posts.each do |p|
-          if users_notified.exclude?(p.user_id)
+        next if users_notified.include?(p.user_id)
+
         p.user.notifications.create(
           notification_type: Notification.types[:moved_post],
           topic_id: p.topic_id,
@@ -28,6 +31,4 @@ module Jobs
       end
     end
   end
-    end
-  end
 end

spec/jobs/notify_moved_posts_spec.rb

@@ -29,6 +29,12 @@ RSpec.describe Jobs::NotifyMovedPosts do
       }.to change(moved_post_notifications, :count).by(2)
     end
 
+    it "notifies on the post with lowest post number" do
+      Jobs::NotifyMovedPosts.new.execute(post_ids: [p1.id, p3.id], moved_by_id: admin.id)
+
+      expect(moved_post_notifications.last.post_number).to eq(p1.post_number)
+    end
+
     context "when moved by one of the posters" do
       it "create one notifications, because the poster is the mover" do
         expect {