Issue #3171391 by mglaman: Only allow JSON:API widget for facets

modules/jsonapi_search_api_facets/jsonapi_search_api_facets.module

 <?php
 
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\facets\FacetInterface;
 use Drupal\facets\FacetSourceInterface;
 use Drupal\jsonapi\Query\Filter;
 
@@ -17,6 +18,20 @@ function jsonapi_search_api_facets_form_facet_source_edit_form_alter(&$form, For
   }
 }
 
+/**
+ * Implements hook_form_FORM_ID_alter().
+ */
+function jsonapi_search_api_facets_form_facets_facet_edit_form_alter(&$form, FormStateInterface $form_state, $form_id) {
+  foreach ($form['widget']['#options'] as $plugin_id => $plugin_name) {
+    if (strpos($plugin_id, 'jsonapi_') !== 0) {
+      unset($form['widget']['#options'][$plugin_id]);
+    }
+  }
+  // Empty behaviors have no effect over JSON:API
+  $form['facet_settings']['empty_behavior']['#access'] = FALSE;
+  $form['facet_settings']['empty_behavior_container']['#access'] = FALSE;
+}
+
 /**
  * Implements hook_ENTITY_TYPE_presave().
  *
@@ -28,3 +43,15 @@ function jsonapi_search_api_facets_facet_source_presave(FacetSourceInterface $en
     $entity->setUrlProcessor('json_api');
   }
 }
+
+/**
+ * Implements hook_ENTITY_TYPE_presave().
+ *
+ */
+function jsonapi_search_api_facets_facets_facet_presave(FacetInterface $entity) {
+  if (strpos($entity->getFacetSourceId(), 'jsonapi_search_api_facets') === 0) {
+    if (empty($entity->getWidget())) {
+      $entity->setWidget('jsonapi_search_api');
+    }
+  }
+}

modules/jsonapi_search_api_facets/tests/src/Functional/IndexFacetsTest.php

@@ -69,8 +69,6 @@ final class IndexFacetsTest extends BrowserTestBase {
     FacetSource::create([
       'id' => 'jsonapi_search_api_facets__database_search_index',
       'name' => 'jsonapi_search_api_facets:database_search_index',
-      'filter_key' => 'filter',
-      'url_processor' => 'json_api',
     ])->save();
   }