Fix specifying a non-default ref when requesting an archive using the legacy URL

app/controllers/projects/repositories_controller.rb

@@ -28,11 +28,12 @@ class Projects::RepositoriesController < Projects::ApplicationController
   end
 
   def assign_archive_vars
-    @id = params[:id]
-
-    return unless @id
-
-    @ref, @filename = extract_ref(@id)
+    if params[:id]
+      @ref, @filename = extract_ref(params[:id])
+    else
+      @ref = params[:ref]
+      @filename = nil
+    end
   rescue InvalidPathError
     render_404
   end

changelogs/unreleased/45507-fix-repository-archive-url.yml

+---
+title: Fix specifying a non-default ref when requesting an archive using the legacy
+  URL
+merge_request: 18468
+author:
+type: fixed

spec/controllers/projects/repositories_controller_spec.rb

@@ -40,6 +40,30 @@ describe Projects::RepositoriesController do
         expect(response.header[Gitlab::Workhorse::SEND_DATA_HEADER]).to start_with("git-archive:")
       end
 
+      it 'handles legacy queries with the ref specified as ref in params' do
+        get :archive, namespace_id: project.namespace, project_id: project, ref: 'feature', format: 'zip'
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(assigns(:ref)).to eq('feature')
+        expect(response.header[Gitlab::Workhorse::SEND_DATA_HEADER]).to start_with("git-archive:")
+      end
+
+      it 'handles legacy queries with the ref specified as id in params' do
+        get :archive, namespace_id: project.namespace, project_id: project, id: 'feature', format: 'zip'
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(assigns(:ref)).to eq('feature')
+        expect(response.header[Gitlab::Workhorse::SEND_DATA_HEADER]).to start_with("git-archive:")
+      end
+
+      it 'prioritizes the id param over the ref param when both are specified' do
+        get :archive, namespace_id: project.namespace, project_id: project, id: 'feature', ref: 'feature_conflict', format: 'zip'
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(assigns(:ref)).to eq('feature')
+        expect(response.header[Gitlab::Workhorse::SEND_DATA_HEADER]).to start_with("git-archive:")
+      end
+
       context "when the service raises an error" do
         before do
           allow(Gitlab::Workhorse).to receive(:send_git_archive).and_raise("Archive failed")