#419

backend/spec/requests/tags_spec.rb

@@ -379,6 +379,37 @@ RSpec.describe 'Tags API', type: :request do
         expect(response).to have_http_status(:not_found)
       end
     end
+
+    it 'falls back to ExternalTag when no internal Tag has the id' do
+      external = create(
+          :external_tag,
+          id: Tag.maximum(:id).to_i + 10_000,
+          name: 'legacy_id_lookup')
+
+      get "/tags/#{ external.id }"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'id' => external.id,
+          'name' => 'nico:legacy_id_lookup',
+          'category' => 'nico')
+    end
+
+    it 'prefers Tag when Tag and ExternalTag have the same id' do
+      internal = create(:tag, name: 'internal_collision')
+      create(
+          :external_tag,
+          id: internal.id,
+          name: 'external_collision')
+
+      get "/tags/#{ internal.id }"
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'id' => internal.id,
+          'name' => 'internal_collision')
+      expect(json.fetch('category')).not_to eq('nico')
+    end
   end
 
   describe 'GET /tags/autocomplete' do

backend/spec/tasks/nico_sync_spec.rb

@@ -16,8 +16,17 @@ RSpec.describe 'nico:sync' do
   end
 
   def create_nico_sanitisation_rules!
-    TagNameSanitisationRule.create!(priority: 20, source_pattern: '\\?', replacement: '_')
-    TagNameSanitisationRule.create!(priority: 40, source_pattern: '_$', replacement: '')
+    TagNameSanitisationRule.create!(priority: 20,
+                                    source_pattern: '\\?',
+                                    replacement: '_')
+
+    TagNameSanitisationRule.create!(priority: 40,
+                                    source_pattern: '_$',
+                                    replacement: '')
+
+    TagNameSanitisationRule.create!(priority: 45,
+                                    source_pattern: '^([^:]+\\:)?_',
+                                    replacement: '\\1')
   end
 
   it '既存 post を見つけて、nico tag と linked tag を追加し、差分が出たら bot を付ける' do
@@ -573,6 +582,7 @@ RSpec.describe 'nico:sync' do
 
   it 'nico: prefix を含む従来の規則で外部タグ名をサニタイズする' do
     post = create_nico_sync_post!
+    create_nico_sanitisation_rules!
 
     run_nico_sync_with_tags!(['foo:_bar'])