FIX: Don't allow parent categories to be deleted. Also, remove

duplicated logic and rely on the server response for `can_delete`
status.

app/assets/javascripts/discourse/controllers/edit_category_controller.js

@@ -58,10 +58,6 @@ Discourse.EditCategoryController = Discourse.ObjectController.extend(Discourse.M
     return false;
   }.property('saving', 'name', 'color', 'deleting'),
 
-  deleteVisible: function() {
-    return (this.get('id') && this.get('topic_count') === 0 && !this.get("isUncategorizedCategory"));
-  }.property('id', 'topic_count'),
-
   deleteDisabled: function() {
     return (this.get('deleting') || this.get('saving') || false);
   }.property('disabled', 'saving', 'deleting'),

app/assets/javascripts/discourse/templates/modal/edit_category.js.handlebars

@@ -119,7 +119,7 @@
   </div>
   <div class="modal-footer">
     <button class='btn btn-primary' {{bind-attr disabled="disabled"}} {{action saveCategory}}>{{buttonTitle}}</button>
-    {{#if deleteVisible}}
+    {{#if can_delete}}
       <button class='btn btn-danger pull-right' {{bind-attr disabled="deleteDisabled"}} {{action deleteCategory}}><i class="fa fa-trash-o"></i>{{deleteButtonTitle}}</button>
     {{/if}}
   </div>

app/models/category.rb

@@ -350,6 +350,10 @@ SQL
     self.where(id: slug.to_i, parent_category_id: parent_category_id).includes(:featured_users).first
   end
 
+  def has_children?
+    id && Category.where(parent_category_id: id).exists?
+  end
+
   def uncategorized?
     id == SiteSetting.uncategorized_category_id
   end

app/serializers/category_serializer.rb

@@ -1,6 +1,11 @@
 class CategorySerializer < BasicCategorySerializer
 
-  attributes :read_restricted, :available_groups, :auto_close_hours, :group_permissions, :position
+  attributes :read_restricted,
+             :available_groups,
+             :auto_close_hours,
+             :group_permissions,
+             :position,
+             :can_delete
 
   def group_permissions
     @group_permissions ||= begin
@@ -21,4 +26,13 @@ class CategorySerializer < BasicCategorySerializer
     Group.order(:name).pluck(:name) - group_permissions.map{|g| g[:group_name]}
   end
 
+
+  def can_delete
+    true
+  end
+
+  def include_can_delete?
+    scope && scope.can_delete?(object)
+  end
+
 end