Resolve #3517343 "Infinite loop with"

Closes #3517343

src/Element/ComponentFormBase.php

@@ -187,12 +187,19 @@ abstract class ComponentFormBase extends FormElementBase implements TrustedCallb
   /**
    * Get source plugin form.
    */
-  protected static function getSourcePluginForm(FormStateInterface $form_state, SourceInterface $source, string $wrapper_id): array {
+  protected static function getSourcePluginForm(FormStateInterface $form_state, ?SourceInterface $source, string $wrapper_id): array {
+    if (!$source) {
+      return [
+        "#type" => 'container',
+        "#attributes" => [
+          'id' => $wrapper_id,
+        ],
+      ];
+    }
     $form = $source->settingsForm([], $form_state);
-    $form["#type"] = 'container';
-    $form['#attributes'] = [
-      'id' => $wrapper_id,
-    ];
+    // @phpstan-ignore-next-line
+    $form['#prefix'] = "<div id='" . $wrapper_id . "'>" . ($form['#prefix'] ?? '');
+    $form['#suffix'] = ($form['#suffix'] ?? '') . "</div>";
     // Weird, but :switchSourceForm() AJAX handler doesn't work without that.
     foreach (Element::children($form) as $child) {
       if (isset($form[$child]['#description']) && !isset($form[$child]['#description_display'])) {
@@ -214,13 +221,17 @@ abstract class ComponentFormBase extends FormElementBase implements TrustedCallb
   /**
    * Get selected source plugin.
    */
-  protected static function getSelectedSource(array $configuration, array $sources): ?SourceInterface {
+  protected static function getSelectedSource(array $configuration, array $sources, bool $auto_select = FALSE): ?SourceInterface {
     $source_id = $configuration['source_id'] ?? NULL;
     foreach ($sources as $source) {
       if ($source->getPluginId() === $source_id) {
         return $source;
       }
     }
+    if (($auto_select && count($sources) > 0) || (count($sources) == 1)) {
+      // Default source is in first position.
+      return current($sources);
+    }
     return NULL;
   }
 
@@ -244,6 +255,28 @@ abstract class ComponentFormBase extends FormElementBase implements TrustedCallb
     return $element;
   }
 
+  /**
+   * Add title and description to the source element.
+   *
+   * @param array $element
+   *   The element.
+   *
+   * @return array
+   *   The element with title and description.
+   */
+  protected static function addTitleAndDescription(array $element): array {
+    if (isset($element["source"]["value"])) {
+      $element["source"]["value"]["#title_display"] = 'before';
+      if (empty($element["source"]["value"]["#title"])) {
+        $element["source"]["value"]["#title"] = $element["#title"];
+      }
+      if (empty($element["source"]["value"]["#description"])) {
+        $element["source"]["value"]["#description"] = $element['#description'] ?? NULL;
+      }
+    }
+    return $element;
+  }
+
   /**
    * Alter the element after the form is built.
    *
@@ -303,7 +336,7 @@ abstract class ComponentFormBase extends FormElementBase implements TrustedCallb
     if (empty($sources)) {
       return [];
     }
-    if (count($sources) == 1) {
+    if ($selected_source && (count($sources) == 1)) {
       return [
         '#type' => 'hidden',
         '#value' => array_keys($sources)[0],
@@ -318,6 +351,7 @@ abstract class ComponentFormBase extends FormElementBase implements TrustedCallb
       '#attributes' => [
         'class' => ["uip-source-selector"],
       ],
+      '#empty_option' => t('- Select -'),
       // '#prop_id' => $selected_source?->getPropId(),
       // '#prop_definition' => $selected_source?->getPropDefinition(),
       '#ajax' => [