Fix Performance Bar, Sentry and Jira Connect App on relative urls

app/assets/javascripts/jira_connect/index.js

+import '../webpack';
+
 import setConfigs from '@gitlab/ui/dist/config';
 import Vue from 'vue';
 import { getLocation, sizeToParent } from '~/jira_connect/utils';

app/assets/javascripts/performance_bar/index.js

+import '../webpack';
+
 import Vue from 'vue';
 import axios from '~/lib/utils/axios_utils';
 import { numberToHumanSize } from '~/lib/utils/number_utils';

app/assets/javascripts/sentry/index.js

+import '../webpack';
+
 import SentryConfig from './sentry_config';
 
 const index = function index() {

app/assets/javascripts/webpack.js

@@ -2,6 +2,9 @@
  * This is the first script loaded by webpack's runtime. It is used to manually configure
  * config.output.publicPath to account for relative_url_root or CDN settings which cannot be
  * baked-in to our webpack bundles.
+ *
+ * Note: This file should be at the top of an entry point and _cannot_ be moved to
+ * e.g. the `window` scope, because it needs to be executed in the scope of webpack.
  */
 
 if (gon && gon.webpack_public_path) {

config/webpack.config.js

@@ -103,6 +103,15 @@ function generateEntries() {
     autoEntries[entry] = defaultEntries.concat(entryPaths);
   });
 
+  /*
+  If you create manual entries, ensure that these import `app/assets/javascripts/webpack.js` right at
+  the top of the entry in order to ensure that the public path is correctly determined for loading
+  assets async. See: https://webpack.js.org/configuration/output/#outputpublicpath
+
+  Note: WebPack 5 has an 'auto' option for the public path which could allow us to remove this option
+  Note 2: If you are using web-workers, you might need to reset the public path, see:
+  https://gitlab.com/gitlab-org/gitlab/-/issues/321656
+   */
   const manualEntries = {
     default: defaultEntries,
     sentry: './sentry/index.js',

qa/qa/specs/features/browser_ui/non_devops/performance_bar_spec.rb

@@ -20,7 +20,7 @@ module QA
           end
         end
 
-        it 'shows results for the original request and AJAX requests', testcase: 'https://gitlab.com/gitlab-org/quality/testcases/-/issues/478', quarantine: { only: { pipeline: :main }, issue: 'https://gitlab.com/gitlab-org/gitlab/-/issues/323051', type: :bug } do
+        it 'shows results for the original request and AJAX requests', testcase: 'https://gitlab.com/gitlab-org/quality/testcases/-/issues/478' do
           # Issue pages always make AJAX requests
           Resource::Issue.fabricate_via_browser_ui! do |issue|
             issue.title = 'Performance bar test'