Return 404 when rendering Repositories#Archive as HTML

app/controllers/projects/repositories_controller.rb

@@ -21,6 +21,8 @@ class Projects::RepositoriesController < Projects::ApplicationController
   end
 
   def archive
+    return render_404 if html_request?
+
     set_cache_headers
     return if archive_not_modified?
 

changelogs/unreleased/archive-404.yml

+---
+title: Return 404 when repository archive cannot be retrieved
+merge_request: 23926
+author:
+type: fixed

spec/controllers/projects/repositories_controller_spec.rb

@@ -88,6 +88,14 @@ describe Projects::RepositoriesController do
         end
       end
 
+      context "when the request format is HTML" do
+        it "renders 404" do
+          get :archive, params: { namespace_id: project.namespace, project_id: project, id: 'master' }, format: "html"
+
+          expect(response).to have_gitlab_http_status(:not_found)
+        end
+      end
+
       describe 'caching' do
         it 'sets appropriate caching headers' do
           get_archive