Issue #2594669 by Wim Leers, borisson_, dawehner, catch: LibraryDependencyResolver::getMinimalRepresentativeSubset() accepts a set as the input but doesn't complain if it's not actually a set

core/lib/Drupal/Core/Asset/LibraryDependencyResolver.php

@@ -65,6 +65,8 @@ class LibraryDependencyResolver implements LibraryDependencyResolverInterface {
    * {@inheritdoc}
    */
   public function getMinimalRepresentativeSubset(array $libraries) {
+    assert('count($libraries) === count(array_unique($libraries))', '$libraries can\'t contain duplicate items.');
+
     $minimal = [];
 
     // Determine each library's dependencies.

core/modules/system/system.module

@@ -766,10 +766,10 @@ function system_js_settings_alter(&$settings, AttachedAssetsInterface $assets) {
     }
     // Provide the page with information about the individual asset libraries
     // used, information not otherwise available when aggregation is enabled.
-    $minimal_libraries = $library_dependency_resolver->getMinimalRepresentativeSubset(array_merge(
+    $minimal_libraries = $library_dependency_resolver->getMinimalRepresentativeSubset(array_unique(array_merge(
       $assets->getLibraries(),
       $assets->getAlreadyLoadedLibraries()
-    ));
+    )));
     sort($minimal_libraries);
     $settings['ajaxPageState']['libraries'] = implode(',', $minimal_libraries);
   }

core/tests/Drupal/Tests/Core/Asset/LibraryDependencyResolverTest.php

@@ -169,4 +169,12 @@ class LibraryDependencyResolverTest extends UnitTestCase {
     $this->assertEquals($expected, $this->libraryDependencyResolver->getMinimalRepresentativeSubset($libraries));
   }
 
+  /**
+   * @covers ::getMinimalRepresentativeSubset
+   */
+  public function testGetMinimalRepresentativeSubsetInvalidInput() {
+    $this->setExpectedException(\AssertionError::class, '$libraries can\'t contain duplicate items.');
+    $this->libraryDependencyResolver->getMinimalRepresentativeSubset(['test/no_deps_a', 'test/no_deps_a']);
+  }
+
 }