Allow placeholder for group link route

Allows us to pass route with placeholder to frontend

config/routes/group.rb

@@ -87,7 +87,7 @@ constraints(::Constraints::GroupUrlConstrainer.new) do
       delete :leave, on: :collection
     end
 
-    resources :group_links, only: [:create, :update, :destroy], constraints: { id: /\d+/ }
+    resources :group_links, only: [:create, :update, :destroy], constraints: { id: /\d+|:id/ }
 
     resources :uploads, only: [:create] do
       collection do

spec/controllers/groups/group_links_controller_spec.rb

@@ -15,6 +15,21 @@ RSpec.describe Groups::GroupLinksController do
     shared_with_group.add_developer(group_member)
   end
 
+  shared_examples 'placeholder is passed as `id` parameter' do |action|
+    it 'returns a 404' do
+      post(
+        action,
+        params: {
+          group_id: shared_group,
+          id: ':id'
+        },
+        format: :json
+      )
+
+      expect(response).to have_gitlab_http_status(:not_found)
+    end
+  end
+
   describe '#create' do
     let(:shared_with_group_id) { shared_with_group.id }
     let(:shared_group_access) { GroupGroupLink.default_access }
@@ -125,6 +140,8 @@ RSpec.describe Groups::GroupLinksController do
         expect(response).to have_gitlab_http_status(:not_found)
       end
     end
+
+    include_examples 'placeholder is passed as `id` parameter', :create
   end
 
   describe '#update' do
@@ -197,6 +214,8 @@ RSpec.describe Groups::GroupLinksController do
         expect(response).to have_gitlab_http_status(:not_found)
       end
     end
+
+    include_examples 'placeholder is passed as `id` parameter', :update
   end
 
   describe '#destroy' do
@@ -232,5 +251,7 @@ RSpec.describe Groups::GroupLinksController do
         expect(response).to have_gitlab_http_status(:not_found)
       end
     end
+
+    include_examples 'placeholder is passed as `id` parameter', :destroy
   end
 end