Issue #3096034 by tim.plunkett, zrpnr: Allow customization of the list of layouts

core/modules/layout_builder/src/Controller/ChooseSectionController.php

@@ -69,8 +69,8 @@ class ChooseSectionController implements ContainerInjectionInterface {
       $item = [
         '#type' => 'link',
         '#title' => [
-          $definition->getIcon(60, 80, 1, 3),
-          [
+          'icon' => $definition->getIcon(60, 80, 1, 3),
+          'label' => [
             '#type' => 'container',
             '#children' => $definition->getLabel(),
           ],
@@ -90,10 +90,10 @@ class ChooseSectionController implements ContainerInjectionInterface {
         $item['#attributes']['data-dialog-type'][] = 'dialog';
         $item['#attributes']['data-dialog-renderer'][] = 'off_canvas';
       }
-      $items[] = $item;
+      $items[$plugin_id] = $item;
     }
     $output['layouts'] = [
-      '#theme' => 'item_list',
+      '#theme' => 'item_list__layouts',
       '#items' => $items,
       '#attributes' => [
         'class' => [

core/modules/layout_builder/tests/modules/layout_builder_field_block_theme_suggestions_test/layout_builder_field_block_theme_suggestions_test.module

@@ -1,19 +0,0 @@
-<?php
-
-/**
- * @file
- * For testing Field Block theme suggestions.
- */
-
-/**
- * Implements hook_theme().
- */
-function layout_builder_field_block_theme_suggestions_test_theme() {
-  // It is necessary to explicitly register the template via hook_theme()
-  // because it is added via a module, not a theme.
-  return [
-    'field__node__body__bundle_with_section_field__default' => [
-      'base hook' => 'field',
-    ],
-  ];
-}

core/modules/layout_builder/tests/modules/layout_builder_theme_suggestions_test/layout_builder_theme_suggestions_test.module

@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * @file
+ * For testing theme suggestions.
+ */
+
+/**
+ * Implements hook_theme().
+ */
+function layout_builder_theme_suggestions_test_theme() {
+  // It is necessary to explicitly register the template via hook_theme()
+  // because it is added via a module, not a theme.
+  return [
+    'field__node__body__bundle_with_section_field__default' => [
+      'base hook' => 'field',
+    ],
+  ];
+}
+
+/**
+ * Implements hook_preprocess_HOOK() for the list of layouts.
+ */
+function layout_builder_theme_suggestions_test_preprocess_item_list__layouts(&$variables) {
+  foreach (array_keys($variables['items']) as $layout_id) {
+    if (isset($variables['items'][$layout_id]['value']['#title']['icon'])) {
+      $variables['items'][$layout_id]['value']['#title']['icon'] = ['#markup' => __FUNCTION__];
+    }
+  }
+}

core/modules/layout_builder/tests/src/Functional/LayoutBuilderThemeSuggestionsTest.php

@@ -5,11 +5,11 @@ namespace Drupal\Tests\layout_builder\Functional;
 use Drupal\Tests\BrowserTestBase;
 
 /**
- * Tests field block template suggestions.
+ * Tests template suggestions.
  *
  * @group layout_builder
  */
-class LayoutBuilderFieldBlockThemeSuggestionsTest extends BrowserTestBase {
+class LayoutBuilderThemeSuggestionsTest extends BrowserTestBase {
 
   /**
    * {@inheritdoc}
@@ -17,7 +17,7 @@ class LayoutBuilderFieldBlockThemeSuggestionsTest extends BrowserTestBase {
   public static $modules = [
     'layout_builder',
     'node',
-    'layout_builder_field_block_theme_suggestions_test',
+    'layout_builder_theme_suggestions_test',
   ];
 
   /**
@@ -54,6 +54,18 @@ class LayoutBuilderFieldBlockThemeSuggestionsTest extends BrowserTestBase {
     $this->drupalPostForm(NULL, ['layout[enabled]' => TRUE], 'Save');
   }
 
+  /**
+   * Tests alterations of the layout list via preprocess functions.
+   */
+  public function testLayoutListSuggestion() {
+    $page = $this->getSession()->getPage();
+    $assert_session = $this->assertSession();
+
+    $this->drupalGet('admin/structure/types/manage/bundle_with_section_field/display/default/layout');
+    $page->clickLink('Add section');
+    $assert_session->pageTextContains('layout_builder_theme_suggestions_test_preprocess_item_list__layouts');
+  }
+
   /**
    * Tests that of view mode specific field templates are suggested.
    */