FEATURE: SiteSetting for creation of small action on tag change (#20812)

This adds a SiteSetting, which when enabled, creates a small_action post for tag/category changes to the topic. It uses `topic.add_moderator_post, and passes raw text in, to describe the change.

config/locales/client.en.yml

@@ -175,6 +175,8 @@ en:
       removed_user: "Removed %{who} %{when}"
       removed_group: "Removed %{who} %{when}"
       autobumped: "Automatically bumped %{when}"
+      tags_changed: "Tags updated %{when}"
+      category_changed: "Category updated %{when}"
       autoclosed:
         enabled: "Closed %{when}"
         disabled: "Opened %{when}"

config/locales/server.en.yml

@@ -61,6 +61,12 @@ en:
   redirect_warning: "We were unable to verify that the link you selected was actually posted to the forum. If you wish to proceed anyway, select the link below."
   on_another_topic: "On another topic"
 
+  topic_category_changed: "From %{from} to %{to}"
+  topic_tag_changed:
+    added_and_removed: "Added %{added} and removed %{removed}"
+    added: "Added %{added}"
+    removed: "Removed %{removed}"
+
   inline_oneboxer:
     topic_page_title_post_number: "#%{post_number}"
     topic_page_title_post_number_by_user: "#%{post_number} by %{username}"
@@ -2353,6 +2359,7 @@ en:
     suppress_overlapping_tags_in_list: "If tags match exact words in topic titles, don't show the tag"
     remove_muted_tags_from_latest: "Don't show topics tagged only with muted tags in the latest topic list."
     force_lowercase_tags: "Force all new tags to be entirely lowercase."
+    create_post_for_category_and_tag_changes: "Create a small action post when a topic's category or tags change"
 
     company_name: "Company Name"
     governing_law: "Governing Law"

config/site_settings.yml

@@ -2788,6 +2788,8 @@ tags:
   force_lowercase_tags:
     default: true
     client: true
+  create_post_for_category_and_tag_changes:
+    default: false
 
 dashboard:
   dashboard_hidden_reports:

lib/post_revisor.rb

@@ -79,25 +79,35 @@ class PostRevisor
     track_and_revise topic_changes, :archetype, attribute
   end
 
-  track_topic_field(:category_id) do |tc, category_id, fields|
-    if category_id == 0 && tc.topic.private_message?
-      tc.record_change("category_id", tc.topic.category_id, nil)
+  track_topic_field(:category_id) do |tc, new_category_id, fields|
+    current_category = tc.topic.category
+    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 category_id == 0 || 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 category_id != 0 &&
+      if new_category &&
            !DiscourseTagging.validate_min_required_tags_for_category(
              tc.guardian,
              tc.topic,
-             Category.find(category_id),
+             new_category,
              tags,
            )
         tc.check_result(false)
         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
 
@@ -114,14 +124,25 @@ 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
@@ -137,6 +158,58 @@ class PostRevisor
     end
   end
 
+  def self.create_small_action_for_category_change(topic:, user:, old_category:, new_category:)
+    return if !SiteSetting.create_post_for_category_and_tag_changes
+
+    topic.add_moderator_post(
+      user,
+      I18n.t(
+        "topic_category_changed",
+        from: category_name_raw(old_category),
+        to: category_name_raw(new_category),
+      ),
+      post_type: Post.types[:small_action],
+      action_code: "category_changed",
+    )
+  end
+
+  def self.category_name_raw(category)
+    "##{CategoryHashtagDataSource.category_to_hashtag_item(category).ref}"
+  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

spec/lib/post_revisor_spec.rb

@@ -146,6 +146,76 @@ RSpec.describe PostRevisor do
 
       expect { subject.revise!(admin, tags: ["new-tag"]) }.not_to change { Notification.count }
     end
+
+    it "doesn't create a small_action post when create_post_for_category_and_tag_changes is false" do
+      SiteSetting.create_post_for_category_and_tag_changes = false
+
+      expect { subject.revise!(admin, tags: ["new-tag"]) }.not_to change { Post.count }
+    end
+
+    describe "when `create_post_for_category_and_tag_changes` site setting is enabled" do
+      fab!(:tag1) { Fabricate(:tag, name: "First tag") }
+      fab!(:tag2) { Fabricate(:tag, name: "Second tag") }
+
+      before { SiteSetting.create_post_for_category_and_tag_changes = true }
+
+      it "Creates a small_action post with correct translation when both adding and removing tags" do
+        post.topic.update!(tags: [tag1])
+
+        expect { subject.revise!(admin, tags: [tag2.name]) }.to change {
+          Post.where(topic_id: post.topic_id, action_code: "tags_changed").count
+        }.by(1)
+
+        expect(post.topic.ordered_posts.last.raw).to eq(
+          I18n.t(
+            "topic_tag_changed.added_and_removed",
+            added: "##{tag2.name}",
+            removed: "##{tag1.name}",
+          ),
+        )
+      end
+
+      it "Creates a small_action post with correct translation when adding tags" do
+        post.topic.update!(tags: [])
+
+        expect { subject.revise!(admin, tags: [tag1.name]) }.to change {
+          Post.where(topic_id: post.topic_id, action_code: "tags_changed").count
+        }.by(1)
+
+        expect(post.topic.ordered_posts.last.raw).to eq(
+          I18n.t("topic_tag_changed.added", added: "##{tag1.name}"),
+        )
+      end
+
+      it "Creates a small_action post with correct translation when removing tags" do
+        post.topic.update!(tags: [tag1, tag2])
+
+        expect { subject.revise!(admin, tags: []) }.to change {
+          Post.where(topic_id: post.topic_id, action_code: "tags_changed").count
+        }.by(1)
+
+        expect(post.topic.ordered_posts.last.raw).to eq(
+          I18n.t("topic_tag_changed.removed", removed: "##{tag1.name}, ##{tag2.name}"),
+        )
+      end
+
+      it "Creates a small_action post when category is changed" do
+        current_category = post.topic.category
+        category = Fabricate(:category)
+
+        expect { subject.revise!(admin, category_id: category.id) }.to change {
+          Post.where(topic_id: post.topic_id, action_code: "category_changed").count
+        }.by(1)
+
+        expect(post.topic.ordered_posts.last.raw).to eq(
+          I18n.t(
+            "topic_category_changed",
+            to: "##{category.slug}",
+            from: "##{current_category.slug}",
+          ),
+        )
+      end
+    end
   end
 
   describe "revise wiki" do