Issue #2884052 by zviryatko, Krzysztof Domański, alexpott, drclaw, vijaycs85, Madis, charlotte.b, mcdruid, Berdir, lauriii: Uploading a managed file on a custom form that allows multiple files also triggers the remove button which results in a duplicate temporary record and results in the file being deleted

(cherry picked from commit 982773dea5)

core/modules/file/file.es6.js

@@ -201,7 +201,7 @@
     triggerUploadButton(event) {
       $(event.target)
         .closest('.js-form-managed-file')
-        .find('.js-form-submit')
+        .find('.js-form-submit[data-drupal-selector$="upload-button"]')
         .trigger('mousedown');
     },
 

core/modules/file/file.js

@@ -92,7 +92,7 @@
       }
     },
     triggerUploadButton: function triggerUploadButton(event) {
-      $(event.target).closest('.js-form-managed-file').find('.js-form-submit').trigger('mousedown');
+      $(event.target).closest('.js-form-managed-file').find('.js-form-submit[data-drupal-selector$="upload-button"]').trigger('mousedown');
     },
     disableFields: function disableFields(event) {
       var $clickedButton = $(this);

core/modules/file/tests/src/FunctionalJavascript/AjaxFileManagedMultipleTest.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace Drupal\Tests\file\FunctionalJavascript;
+
+use Drupal\Core\Url;
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+use Drupal\Tests\TestFileCreationTrait;
+
+/**
+ * Tests ajax upload to managed files.
+ *
+ * @group file
+ */
+class AjaxFileManagedMultipleTest extends WebDriverTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['file_test', 'file', 'file_module_test'];
+
+  /**
+   * Test if managed file form element works well with multiple files upload.
+   */
+  public function testMultipleFilesUpload() {
+    $file_system = \Drupal::service('file_system');
+    $file_storage = \Drupal::entityTypeManager()->getStorage('file');
+    $page = $this->getSession()->getPage();
+
+    $this->drupalGet(Url::fromRoute('file_module_test.managed_test', ['multiple' => TRUE]));
+
+    $paths = [];
+    foreach (array_slice($this->drupalGetTestFiles('image'), 0, 2) as $image) {
+      $paths[] = $image->filename;
+      $page->attachFileToField('files[nested_file][]', $file_system->realpath($image->uri));
+      $this->assertSession()->assertWaitOnAjaxRequest();
+    }
+
+    // Save entire form.
+    $page->pressButton('Save');
+
+    $this->assertSession()->pageTextContains('The file ids are 1,2.');
+    $this->assertCount(2, $file_storage->loadByProperties(['filename' => $paths]));
+  }
+
+}