FIX: Correct slug validation

We were allowing new categories to use slugs like "2342-category".

app/models/category.rb

@@ -294,10 +294,11 @@ class Category < ActiveRecord::Base
       self.slug = Slug.for(name, '')
       self.slug = '' if duplicate_slug?
     end
-    # only allow to use category itself id. new_record doesn't have a id.
-    unless new_record?
-      match_id = /^(\d+)-category/.match(self.slug)
-      errors.add(:slug, :invalid) if match_id && match_id[1] && match_id[1] != self.id.to_s
+
+    # only allow to use category itself id.
+    match_id = /^(\d+)-/.match(self.slug)
+    if match_id.present?
+      errors.add(:slug, :invalid) if new_record? || (match_id[1] != self.id.to_s)
     end
   end
 

spec/requests/list_controller_spec.rb

@@ -400,7 +400,17 @@ RSpec.describe ListController do
 
       context 'another category exists with a number at the beginning of its name' do
         # One category has another category's id at the beginning of its name
-        let!(:other_category) { Fabricate(:category_with_definition, name: "#{category.id} name") }
+        let!(:other_category) {
+          # Our validations don't allow this to happen now, but did historically
+          Fabricate(:category_with_definition, name: "#{category.id} name", slug: '-').tap { |c|
+            DB.exec <<~SQL
+              UPDATE categories
+              SET slug = '#{category.id}-name'
+              WHERE id = #{c.id}
+            SQL
+            c.reload
+          }
+        }
 
         it 'uses the correct category' do
           get "/c/#{other_category.slug}/l/latest.json"