Add delete method in Release API

Introduce DELETE endpoint in Release API

app/services/delete_release_service.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class DeleteReleaseService < BaseService
+  include Gitlab::Utils::StrongMemoize
+
+  def execute
+    return error('Tag does not exist', 404) unless existing_tag
+    return error('Release does not exist', 404) unless release
+    return error('Access Denied', 403) unless allowed?
+
+    if release.destory
+      success(release: release)
+    else
+      error(release.errors.messages || '400 Bad request', 400)
+    end
+  end
+
+  private
+
+  def allowed?
+    Ability.allowed?(current_user, :admin_release, release)
+  end
+
+  def release
+    strong_memoize(:release) do
+      project.releases.find_by_tag(@tag_name)
+    end
+  end
+
+  def existing_tag
+    strong_memoize(:existing_tag) do
+      repository.find_tag(@tag_name)
+    end
+  end
+
+  def repository
+    strong_memoize(:repository) do
+      project.repository
+    end
+  end  
+end

lib/api/releases.rb

@@ -89,6 +89,27 @@ module API
           render_api_error!(result[:message], result[:http_status])
         end
       end
+
+      desc 'Delete a release' do
+        detail 'This feature was introduced in GitLab 11.7.'
+        success Entities::Release
+      end
+      params do
+        requires :tag_name,    type: String, desc: 'The name of the tag', as: :tag
+      end
+      delete ':id/releases/:tag_name', requirements: RELEASE_ENDPOINT_REQUIREMETS do
+        authorize_update_release!
+
+        attributes = declared(params)
+        attributes.delete(:id)
+        result = DeleteReleaseService.new(user_project, current_user, attributes).execute
+
+        if result[:status] == :success
+          present result[:release], with: Entities::Release
+        else
+          render_api_error!(result[:message], result[:http_status])
+        end
+      end
     end
   end
 end

spec/requests/api/releases_spec.rb

@@ -0,0 +1,35 @@
+require 'spec_helper'
+
+describe API::Releases do
+  let(:user) { create(:user) }
+  let(:guest) { create(:user).tap { |u| project.add_guest(u) } }
+  let(:project) { create(:project, :repository, creator: user, path: 'my.project') }
+  let(:tag_name) { project.repository.find_tag('v1.1.0').name }
+
+  let(:project_id) { project.id }
+  let(:current_user) { nil }
+
+  before do
+    project.add_maintainer(user)
+  end
+
+  describe 'GET /projects/:id/releases' do
+    # TODO:
+  end
+
+  describe 'GET /projects/:id/releases/:tag_name' do
+    # TODO:
+  end
+
+  describe 'POST /projects/:id/releases' do
+    # TODO:
+  end
+
+  describe 'PUT /projects/:id/releases/:tag_name' do
+    # TODO:
+  end
+
+  describe 'DELETE /projects/:id/releases/:tag_name' do
+    # TODO:
+  end
+end

spec/services/delete_release_service_spec.rb

@@ -0,0 +1 @@
+#TODO: