Fix npm registry for yarn

Expose dist-tags attribute in NPM registry API
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

ee/app/presenters/npm_package_presenter.rb

@@ -25,15 +25,21 @@ class NpmPackagePresenter
     package_versions
   end
 
+  def dist_tags
+    {
+      latest: sorted_versions.last
+    }
+  end
+
   private
 
   def build_package_version(package, package_file)
     {
-      "name": package.name,
-      "version": package.version,
-      "dist": {
-        "shasum": package_file.file_sha1,
-        "tarball": tarball_url(package, package_file)
+      name: package.name,
+      version: package.version,
+      dist: {
+        shasum: package_file.file_sha1,
+        tarball: tarball_url(package, package_file)
       }
     }
   end
@@ -43,4 +49,9 @@ class NpmPackagePresenter
       "/packages/npm/#{package.name}" \
       "/-/#{package_file.file_name}"
   end
+
+  def sorted_versions
+    versions = packages.map(&:version).compact
+    VersionSorter.sort(versions)
+  end
 end

ee/changelogs/unreleased/dz-npm-registry-yarn-support.yml

+---
+title: Fix npm registry for yarn
+merge_request: 9599
+author:
+type: fixed

ee/lib/ee/api/entities.rb

@@ -629,6 +629,7 @@ module EE
       class NpmPackage < Grape::Entity
         expose :name
         expose :versions
+        expose :dist_tags, as: 'dist-tags'
       end
 
       class Package < Grape::Entity

ee/spec/presenters/npm_package_presenter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe NpmPackagePresenter do
+  set(:project) { create(:project) }
+  set(:package) { create(:npm_package, version: '1.0.4', project: project) }
+  set(:latest_package) { create(:npm_package, version: '1.0.11', project: project) }
+  let(:presenter) { described_class.new(project, package.name, project.packages.all) }
+
+  describe '#dist_tags' do
+    it { expect(presenter.dist_tags).to be_a(Hash) }
+    it { expect(presenter.dist_tags[:latest]).to eq(latest_package.version) }
+  end
+
+  describe '#versions' do
+    it { expect(presenter.versions).to be_a(Hash) }
+    it { expect(presenter.versions[package.version]).to match_schema('public_api/v4/packages/npm_package_version', dir: 'ee') }
+  end
+end