This is a really tricky issue to reproduce and debug:
When I debug this locally, I learn that the library being duplicated is "core/components.navigation--toolbar-button". During the BigPipe lazy loader, the "NavigationUserBlock" is causing this library to be added 5 times.
This happens when Drupal initially creating the CSS/JS aggregation files. If I visit the page manually in a browser, I do not get any error and that causes the aggregated files to be created properly. After creating the aggregated files, running the ExistingSiteTest no longer errors.
I can prevent the error by disabling the placeholder in NavigationUserBlock ('#create_placeholder' => FALSE), but that's not really a solution. I can also prevent the error by disabling the Navigation module completely and going back to AdminToolbar.
If I visit the home page manually in a browser after clearing cache, this error does not occur, nor is it in the recent log messages. So it's possible this is somehow related to building the CSS/JS cache from ExistingSiteText. I realize that makes it more difficult to reproduce since that's not part of Core. But I'm posting this in case someone else more experienced with this lazy building process has any idea what might be causing it so it can hopefully be fixed before Navigation is no longer experimental.
This was reproduced in a fresh version of Drupal CMS 1.0 on Drupal 11.1.2, php8.3.6.
Full error dump (not that I found it very helpful):
Exception: $libraries can't contain duplicate items. Duplicate libraries: core/components.navigation--toolbar-button in Drupal\Core\Asset\LibraryDependencyResolver->getMinimalRepresentativeSubset() (line 85 of /var/www/docroot/core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php)
#0 /var/www/docroot/core/lib/Drupal/Core/Asset/CssCollectionOptimizerLazy.php(112): Drupal\Core\Asset\LibraryDependencyResolver->getMinimalRepresentativeSubset(Array)
#1 /var/www/docroot/core/lib/Drupal/Core/Asset/AssetResolver.php(251): Drupal\Core\Asset\CssCollectionOptimizerLazy->optimize(Array, Array, Object(Drupal\Core\Language\Language))
#2 /var/www/docroot/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php(279): Drupal\Core\Asset\AssetResolver->getCssAssets(Object(Drupal\Core\Asset\AttachedAssets), true, Object(Drupal\Core\Language\Language))
#3 /var/www/docroot/core/lib/Drupal/Core/Render/HtmlResponseAttachmentsProcessor.php(123): Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAssetLibraries(Object(Drupal\Core\Asset\AttachedAssets), Array)
#4 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipeResponseAttachmentsProcessor.php(97): Drupal\Core\Render\HtmlResponseAttachmentsProcessor->processAttachments(Object(Drupal\Core\Render\HtmlResponse))
#5 /var/www/docroot/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php(45): Drupal\big_pipe\Render\BigPipeResponseAttachmentsProcessor->processAttachments(Object(Drupal\Core\Render\HtmlResponse))
#6 /var/www/vendor/symfony/event-dispatcher/EventDispatcher.php(206): Drupal\Core\EventSubscriber\HtmlResponseSubscriber->onRespond(Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response', Object(Symfony\Component\EventDispatcher\EventDispatcher))
#7 /var/www/vendor/symfony/event-dispatcher/EventDispatcher.php(56): Symfony\Component\EventDispatcher\EventDispatcher->callListeners(Array, 'kernel.response', Object(Symfony\Component\HttpKernel\Event\ResponseEvent))
#8 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipe.php(668): Symfony\Component\EventDispatcher\EventDispatcher->dispatch(Object(Symfony\Component\HttpKernel\Event\ResponseEvent), 'kernel.response')
#9 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipe.php(646): Drupal\big_pipe\Render\BigPipe->filterResponse(Object(Symfony\Component\HttpFoundation\Request), 2, Object(Drupal\Core\Render\HtmlResponse))
#10 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipe.php(413): Drupal\big_pipe\Render\BigPipe->filterEmbeddedResponse(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Render\HtmlResponse))
#11 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipe.php(279): Drupal\big_pipe\Render\BigPipe->sendNoJsPlaceholders('<!DOCTYPE html>...', Array, Object(Drupal\Core\Asset\AttachedAssets))
#12 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipe.php(247): Drupal\big_pipe\Render\BigPipe->sendPreBody('<!DOCTYPE html>...', Array, Object(Drupal\Core\Asset\AttachedAssets))
#13 /var/www/docroot/core/modules/big_pipe/src/Render/BigPipeResponse.php(113): Drupal\big_pipe\Render\BigPipe->sendContent(Object(Drupal\big_pipe\Render\BigPipeResponse))
#14 /var/www/vendor/symfony/http-foundation/Response.php(395): Drupal\big_pipe\Render\BigPipeResponse->sendContent()
#15 /var/www/docroot/index.php(20): Symfony\Component\HttpFoundation\Response->send()
#16 {main}Active
11.1 🔥
navigation.module
Hmm, this is interesting. I just switched the Admin theme from Gin to Claro and the error went away. So this might even be a Gin issue.
Changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to the Core change policies → .