Only include fields used by the frontend

To avoid loading tags and project_import_data
even though it's not used,
we now only select the id and name of the project which
are the only 2 attributes used on the frontend.

This prevents fetching unused data and an N+1 query
on projects.

https://gitlab.com/gitlab-org/gitlab/-/issues/21044

changelogs/unreleased/21044-controller-profiles-slackscontroller-edit-executes-more-than-100-sq.yml

+---
+title: Reduce number of SQL queries in Profiles::SlacksController#edit
+merge_request: 57674
+author:
+type: performance

ee/app/controllers/profiles/slacks_controller.rb

@@ -10,7 +10,7 @@ class Profiles::SlacksController < Profiles::ApplicationController
   feature_category :users
 
   def edit
-    @projects = disabled_projects if current_user
+    @projects = disabled_projects.select([:id, :name]) if current_user
   end
 
   def slack_link

ee/app/helpers/ee/services_helper.rb

@@ -36,7 +36,7 @@ module EE
 
     def add_to_slack_data(projects)
       {
-        projects: projects,
+        projects: projects.as_json(only: [:id, :name]),
         sign_in_path: new_session_path(:user, redirect_to_referer: 'yes'),
         is_signed_in: current_user.present?,
         slack_link_profile_slack_path: slack_link_profile_slack_path,

ee/spec/helpers/ee/services_helper_spec.rb

@@ -3,9 +3,12 @@
 require 'spec_helper'
 
 RSpec.describe EE::ServicesHelper do
+  include Devise::Test::ControllerHelpers
+
   let(:controller_class) do
     Class.new(ActionController::Base) do
       include EE::ServicesHelper
+      include ActionView::Helpers::AssetUrlHelper
 
       def slack_auth_project_settings_slack_url(project)
         "http://some-path/project/1"
@@ -111,4 +114,54 @@ RSpec.describe EE::ServicesHelper do
       is_expected.to include(:issues_show_path)
     end
   end
+
+  describe '#add_to_slack_data' do
+    let_it_be(:projects) { create_list(:project, 3) }
+
+    def relation
+      Project.id_in(projects.pluck(:id))
+    end
+
+    let(:request) do
+      double(:Request,
+             optional_port: nil,
+             path_parameters: {},
+             protocol: 'https',
+             routes: nil,
+             env: { 'warden' => warden },
+             engine_script_name: nil,
+             original_script_name: nil,
+             host: 'example.com')
+    end
+
+    before do
+      allow(subject).to receive(:request).and_return(request)
+    end
+
+    it 'includes the required keys' do
+      additions = Gitlab::Json.parse(subject.add_to_slack_data(relation))
+      expect(additions.keys).to match_array %w[
+        projects
+        sign_in_path
+        is_signed_in
+        slack_link_profile_slack_path
+        gitlab_for_slack_gif_path
+        gitlab_logo_path
+        slack_logo_path
+        docs_path
+      ]
+    end
+
+    it 'does not suffer from N+1 performance issues' do
+      baseline = ActiveRecord::QueryRecorder.new { subject.add_to_slack_data(relation.limit(1)) }
+
+      expect do
+        subject.add_to_slack_data(relation)
+      end.not_to exceed_query_limit(baseline)
+    end
+
+    it 'serializes nil projects without error' do
+      expect(subject.add_to_slack_data(nil)).to include('"projects":null')
+    end
+  end
 end