Revert "DEV: Removal of create_post_for_category_and_tag_changes setting (#28…" (#28587)

This reverts commit fc33826dc5.

lib/post_revisor.rb

@@ -79,14 +79,15 @@ class PostRevisor
     track_and_revise topic_changes, :archetype, attribute
   end
 
-  track_topic_field(:category_id) do |tc, category_id, fields|
+  track_topic_field(:category_id) do |tc, new_category_id, fields|
     current_category = tc.topic.category
-    new_category = (category_id.nil? || category_id.zero?) ? nil : Category.find(category_id)
+    new_category =
+      (new_category_id.nil? || new_category_id.zero?) ? nil : Category.find(new_category_id)
 
     if new_category.nil? && tc.topic.private_message?
       tc.record_change("category_id", current_category.id, nil)
       tc.topic.category_id = nil
-    elsif new_category.nil? || tc.guardian.can_move_topic_to_category?(category_id)
+    elsif new_category.nil? || tc.guardian.can_move_topic_to_category?(new_category_id)
       tags = fields[:tags] || tc.topic.tags.map(&:name)
       if new_category &&
            !DiscourseTagging.validate_category_tags(tc.guardian, tc.topic, new_category, tags)
@@ -94,8 +95,14 @@ class PostRevisor
         next
       end
 
-      tc.record_change("category_id", tc.topic.category_id, category_id)
-      tc.check_result(tc.topic.change_category_to_id(category_id))
+      tc.record_change("category_id", current_category&.id, new_category&.id)
+      tc.check_result(tc.topic.change_category_to_id(new_category_id))
+      create_small_action_for_category_change(
+        topic: tc.topic,
+        user: tc.user,
+        old_category: current_category,
+        new_category: new_category,
+      )
     end
   end
 
@@ -112,14 +119,25 @@ class PostRevisor
         DB.after_commit do
           post = tc.topic.ordered_posts.first
           notified_user_ids = [post.user_id, post.last_editor_id].uniq
+
+          added_tags = tags - prev_tags
+          removed_tags = prev_tags - tags
+
           if !SiteSetting.disable_tags_edit_notifications
             Jobs.enqueue(
               :notify_tag_change,
               post_id: post.id,
               notified_user_ids: notified_user_ids,
-              diff_tags: ((tags - prev_tags) | (prev_tags - tags)),
+              diff_tags: (added_tags | removed_tags),
             )
           end
+
+          create_small_action_for_tag_changes(
+            topic: tc.topic,
+            user: tc.user,
+            added_tags: added_tags,
+            removed_tags: removed_tags,
+          )
         end
       end
     end
@@ -135,6 +153,56 @@ class PostRevisor
     end
   end
 
+  def self.create_small_action_for_category_change(topic:, user:, old_category:, new_category:)
+    if !old_category || !new_category || !SiteSetting.create_post_for_category_and_tag_changes
+      return
+    end
+
+    topic.add_moderator_post(
+      user,
+      I18n.t(
+        "topic_category_changed",
+        from: "##{old_category.slug_ref}",
+        to: "##{new_category.slug_ref}",
+      ),
+      post_type: Post.types[:small_action],
+      action_code: "category_changed",
+    )
+  end
+
+  def self.create_small_action_for_tag_changes(topic:, user:, added_tags:, removed_tags:)
+    return if !SiteSetting.create_post_for_category_and_tag_changes
+
+    topic.add_moderator_post(
+      user,
+      tags_changed_raw(added: added_tags, removed: removed_tags),
+      post_type: Post.types[:small_action],
+      action_code: "tags_changed",
+      custom_fields: {
+        tags_added: added_tags,
+        tags_removed: removed_tags,
+      },
+    )
+  end
+
+  def self.tags_changed_raw(added:, removed:)
+    if removed.present? && added.present?
+      I18n.t(
+        "topic_tag_changed.added_and_removed",
+        added: tag_list_to_raw(added),
+        removed: tag_list_to_raw(removed),
+      )
+    elsif added.present?
+      I18n.t("topic_tag_changed.added", added: tag_list_to_raw(added))
+    elsif removed.present?
+      I18n.t("topic_tag_changed.removed", removed: tag_list_to_raw(removed))
+    end
+  end
+
+  def self.tag_list_to_raw(tag_list)
+    tag_list.sort.map { |tag_name| "##{tag_name}" }.join(", ")
+  end
+
   # AVAILABLE OPTIONS:
   # - revised_at: changes the date of the revision
   # - force_new_version: bypass grace period edit window