FEATURE: Allow Category Group Moderators to edit topic titles (#11340)

* FEATURE: Allow Category Group Moderators to edit topic titles

Adds category group moderators to the topic guardian’s `can_edit` method.

The value of `can_edit` is returned by the topic view serializer, and this value determines whether the current user can edit the title/category/tags of the topic directly (which category group moderators could already do by editing the first post of a topic).

Note that the value of `can_edit` is now always returned by the topic view serializer (ie, for both true and false values) to cover the case where a topic is moved out of a category that a category group moderator has permissions on, so that when the topic is reloaded the UI picks up that `can_edit` is now false, and thus the edit icon should no longer be displayed.

* DEV: Add a comment explaining why `can_edit` is always returned

app/serializers/topic_view_details_serializer.rb

@@ -4,7 +4,6 @@ class TopicViewDetailsSerializer < ApplicationSerializer
 
   def self.can_attributes
     [:can_move_posts,
-     :can_edit,
      :can_delete,
      :can_recover,
      :can_remove_allowed_users,
@@ -24,7 +23,10 @@ class TopicViewDetailsSerializer < ApplicationSerializer
      :can_moderate_category]
   end
 
+  # NOTE: `can_edit` is defined as an attribute because we explicitly want
+  # it returned even if it has a value of `false`
   attributes(
+    :can_edit,
     :notification_level,
     :notifications_reason_id,
     *can_attributes,
@@ -87,6 +89,13 @@ class TopicViewDetailsSerializer < ApplicationSerializer
     define_method(ca) { true }
   end
 
+  # NOTE: A Category Group Moderator moving a topic to a different category
+  # may result in the 'can_edit?' result changing from `true` to `false`.
+  # Explictly returning a `false` value is required to update the client UI.
+  def can_edit
+    scope.can_edit?(object.topic)
+  end
+
   def include_can_review_topic?
     scope.can_review_topic?(object.topic)
   end
@@ -95,10 +104,6 @@ class TopicViewDetailsSerializer < ApplicationSerializer
     scope.can_move_posts?(object.topic)
   end
 
-  def include_can_edit?
-    scope.can_edit?(object.topic)
-  end
-
   def include_can_delete?
     scope.can_delete?(object.topic)
   end

lib/guardian/topic_guardian.rb

@@ -79,6 +79,7 @@ module TopicGuardian
 
     return true if is_admin?
     return true if is_moderator? && can_create_post?(topic)
+    return true if is_category_group_moderator?(topic.category)
 
     # can't edit topics in secured categories where you don't have permission to create topics
     # except for a tiny edge case where the topic is uncategorized and you are trying

spec/serializers/topic_view_serializer_spec.rb

@@ -365,6 +365,27 @@ describe TopicViewSerializer do
         expect(json[:details][:can_edit_tags]).to eq(true)
       end
     end
+
+    context "can_edit" do
+      fab!(:group_user) { Fabricate(:group_user) }
+      fab!(:category) { Fabricate(:category, reviewable_by_group: group_user.group) }
+      fab!(:topic) { Fabricate(:topic, category: category) }
+      let(:user) { group_user.user }
+
+      before do
+        SiteSetting.enable_category_group_moderation = true
+      end
+
+      it 'explicitly returns can_edit' do
+        json = serialize_topic(topic, user)
+        expect(json[:details][:can_edit]).to eq(true)
+
+        topic.update!(category: nil)
+
+        json = serialize_topic(topic, user)
+        expect(json[:details][:can_edit]).to eq(false)
+      end
+    end
   end
 
   context "published_page" do