Issue #1953444 by amateescu, xjm: Make 'target bundles' required on the Entity...

Issue #1953444 by amateescu, xjm: Make 'target bundles' required on the Entity reference instance settings form to help increase their visibility/sanity.

core/modules/entity_reference/lib/Drupal/entity_reference/Plugin/entity_reference/selection/SelectionBase.php

@@ -97,7 +97,8 @@ public static function settingsForm(&$field, &$instance) {
         '#type' => 'checkboxes',
         '#title' => $target_bundles_title,
         '#options' => $bundle_options,
-        '#default_value' => (!empty($instance['settings']['handler_settings']['target_bundles'])) ? $instance['settings']['handler_settings']['target_bundles'] : array_keys($bundle_options),
+        '#default_value' => (!empty($instance['settings']['handler_settings']['target_bundles'])) ? $instance['settings']['handler_settings']['target_bundles'] : array(),
+        '#required' => TRUE,
         '#size' => 6,
         '#multiple' => TRUE,
         '#element_validate' => array('_entity_reference_element_validate_filter'),

core/modules/entity_reference/lib/Drupal/entity_reference/Tests/EntityReferenceAdminTest.php

@@ -100,7 +100,9 @@ public function testFieldAdminHandler() {
     $this->drupalPostAJAX(NULL, array('instance[settings][handler_settings][sort][field]' => '_none'), 'instance[settings][handler_settings][sort][field]');
 
     // Third step: confirm.
-    $this->drupalPost(NULL, array(), t('Save settings'));
+    $this->drupalPost(NULL, array(
+      'instance[settings][handler_settings][target_bundles][' . key($bundles) . ']' => key($bundles),
+    ), t('Save settings'));
 
     // Check that the field appears in the overview form.
     $this->assertFieldByXPath('//table[@id="field-overview"]//td[1]', 'Test label', t('Field was created and appears in the overview page.'));