Issue #2662574 by RajeevK, Adita, pritish.kumar, afi13, AjitS, greyghost: Theme suggestions may not be in theme include files, Search and Views UI suggestions are not (always) found

core/lib/Drupal/Core/Render/theme.api.php

@@ -613,6 +613,10 @@ function hook_preprocess_HOOK(&$variables) {
  * hook called (in this case 'node__article') is available in
  * $variables['theme_hook_original'].
  *
+ * Implementations of this hook must be placed in *.module or *.theme files, or
+ * must otherwise make sure that the hook implementation is available at
+ * any given time.
+ *
  * @todo Add @code sample.
  *
  * @param array $variables
@@ -694,6 +698,10 @@ function hook_theme_suggestions_alter(array &$suggestions, array $variables, $ho
  * hook called (in this case 'node__article') is available in
  * $variables['theme_hook_original'].
  *
+ * Implementations of this hook must be placed in *.module or *.theme files, or
+ * must otherwise make sure that the hook implementation is available at
+ * any given time.
+ *
  * @todo Add @code sample.
  *
  * @param array $suggestions

core/modules/search/search.module

@@ -106,6 +106,13 @@ function search_theme() {
   ];
 }
 
+/**
+ * Implements hook_theme_suggestions_HOOK().
+ */
+function search_theme_suggestions_search_result(array $variables) {
+  return ['search_result__' . $variables['plugin_id']];
+}
+
 /**
  * Implements hook_preprocess_HOOK() for block templates.
  */

core/modules/search/search.pages.inc

@@ -8,13 +8,6 @@
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Language\LanguageInterface;
 
-/**
- * Implements hook_theme_suggestions_HOOK().
- */
-function search_theme_suggestions_search_result(array $variables) {
-  return ['search_result__' . $variables['plugin_id']];
-}
-
 /**
  * Prepares variables for individual search result templates.
  *

core/modules/views_ui/views_ui.module

@@ -156,6 +156,13 @@ function views_ui_preprocess_views_view(&$variables) {
   }
 }
 
+/**
+ * Implements hook_theme_suggestions_HOOK().
+ */
+function views_ui_theme_suggestions_views_ui_view_preview_section(array $variables) {
+  return ['views_ui_view_preview_section__' . $variables['section']];
+}
+
 /**
  * Returns contextual links for each handler of a certain section.
  *

core/modules/views_ui/views_ui.theme.inc

@@ -547,10 +547,3 @@ function template_preprocess_views_ui_view_preview_section(&$variables) {
     $variables['links'] = $build;
   }
 }
-
-/**
- * Implements hook_theme_suggestions_HOOK().
- */
-function views_ui_theme_suggestions_views_ui_view_preview_section(array $variables) {
-  return ['views_ui_view_preview_section__' . $variables['section']];
-}