diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index f98df80..900219f 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2794,6 +2794,7 @@ function drupal_common_theme() {
     ),
     'table' => array(
       'variables' => array('header' => NULL, 'rows' => NULL, 'attributes' => array(), 'caption' => NULL, 'colgroups' => array(), 'sticky' => FALSE, 'responsive' => TRUE, 'empty' => ''),
+      'function' => 'theme_table',
     ),
     'tablesort_indicator' => array(
       'variables' => array('style' => NULL),
@@ -2801,6 +2802,7 @@ function drupal_common_theme() {
     ),
     'mark' => array(
       'variables' => array('status' => MARK_NEW),
+      'function' => 'theme_mark',
     ),
     'item_list' => array(
       'variables' => array('items' => array(), 'title' => '', 'list_type' => 'ul', 'attributes' => array(), 'empty' => NULL),
@@ -2811,7 +2813,8 @@ function drupal_common_theme() {
       'template' => 'feed-icon',
     ),
     'more_link' => array(
-      'variables' => array('url' => NULL, 'title' => NULL)
+      'variables' => array('url' => NULL, 'title' => NULL),
+      'function' => 'theme_more_link',
     ),
     'progress_bar' => array(
       'variables' => array('label' => NULL, 'percent' => NULL, 'message' => NULL),
@@ -2819,6 +2822,7 @@ function drupal_common_theme() {
     ),
     'indentation' => array(
       'variables' => array('size' => 1),
+      'function' => 'theme_indentation',
     ),
     // From theme.maintenance.inc.
     'maintenance_page' => array(
@@ -2831,12 +2835,15 @@ function drupal_common_theme() {
     ),
     'task_list' => array(
       'variables' => array('items' => NULL, 'active' => NULL,  'variant' => NULL),
+      'function' => 'theme_task_list',
     ),
     'authorize_message' => array(
       'variables' => array('message' => NULL, 'success' => TRUE),
+      'function' => 'theme_authorize_message',
     ),
     'authorize_report' => array(
       'variables' => array('messages' => array()),
+      'function' => 'theme_authorize_report',
     ),
     // From pager.inc.
     'pager' => array(
@@ -2846,22 +2853,28 @@ function drupal_common_theme() {
     // From menu.inc.
     'menu_link' => array(
       'render element' => 'element',
+      'function' => 'theme_menu_link',
     ),
     'menu_tree' => array(
       'render element' => 'tree',
+      'function' => 'theme_menu_tree',
     ),
     'menu_local_task' => array(
       'render element' => 'element',
+      'function' => 'theme_menu_local_task',
     ),
     'menu_local_action' => array(
       'render element' => 'element',
+      'function' => 'theme_menu_local_action',
     ),
     'menu_local_tasks' => array(
       'variables' => array('primary' => array(), 'secondary' => array()),
+      'function' => 'theme_menu_local_tasks',
     ),
     // From form.inc.
     'input' => array(
       'render element' => 'element',
+      'function' => 'theme_input',
     ),
     'select' => array(
       'render element' => 'element',
@@ -2881,9 +2894,11 @@ function drupal_common_theme() {
     ),
     'date' => array(
       'render element' => 'element',
+      'function' => 'theme_date',
     ),
     'checkboxes' => array(
       'render element' => 'element',
+      'function' => 'theme_checkboxes',
     ),
     'form' => array(
       'render element' => 'element',
@@ -2895,6 +2910,7 @@ function drupal_common_theme() {
     ),
     'tableselect' => array(
       'render element' => 'element',
+      'function' => 'theme_tableselect',
     ),
     'form_element' => array(
       'render element' => 'element',
@@ -2902,9 +2918,11 @@ function drupal_common_theme() {
     ),
     'form_required_marker' => array(
       'render element' => 'element',
+      'function' => 'theme_form_required_marker',
     ),
     'form_element_label' => array(
       'render element' => 'element',
+      'function' => 'theme_form_element_label',
     ),
     'vertical_tabs' => array(
       'render element' => 'element',
diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index e84b33b..449badf 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -426,7 +426,9 @@ protected function processExtension(&$cache, $name, $type, $theme, $path) {
         // If function and file are omitted, default to standard naming
         // conventions.
         if (!isset($info['template']) && !isset($info['function'])) {
-          $result[$hook]['function'] = ($type == 'module' ? 'theme_' : $name . '_') . $hook;
+          $template_name = strtr($hook, '_', '-');
+          $info['template'] = $template_name;
+          $result[$hook]['template'] = $template_name;
         }
 
         if (isset($cache[$hook]['includes'])) {
diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index 86011d6..66a4abb 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -78,10 +78,12 @@ function aggregator_theme() {
     'aggregator_page_opml' => array(
       'variables' => array('feeds' => NULL),
       'file' => 'aggregator.theme.inc',
+      'function' => 'theme_aggregator_page_opml',
     ),
     'aggregator_page_rss' => array(
       'variables' => array('feeds' => NULL),
       'file' => 'aggregator.theme.inc',
+      'function' => 'theme_aggregator_page_rss',
     ),
   );
 }
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index fca7d44..ff1b7ec 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -56,6 +56,7 @@ function book_theme() {
     ),
     'book_link' => array(
       'render element' => 'element',
+      'function' => 'theme_book_link',
     ),
     'book_export_html' => array(
       'variables' => array('title' => NULL, 'contents' => NULL, 'depth' => NULL),
@@ -64,6 +65,7 @@ function book_theme() {
     'book_admin_table' => array(
       'render element' => 'form',
       'file' => 'book.admin.inc',
+      'function' => 'theme_book_admin_table',
     ),
     'book_all_books_block' => array(
       'render element' => 'book_menus',
diff --git a/core/modules/field_ui/field_ui.module b/core/modules/field_ui/field_ui.module
index 40c8f28..285a41b 100644
--- a/core/modules/field_ui/field_ui.module
+++ b/core/modules/field_ui/field_ui.module
@@ -99,6 +99,7 @@ function field_ui_theme() {
   return array(
     'field_ui_table' => array(
       'render element' => 'elements',
+      'function' => 'theme_field_ui_table',
     ),
   );
 }
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 3843be9..71ec63f 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -568,26 +568,33 @@ function file_theme() {
     // file.module.
     'file_link' => array(
       'variables' => array('file' => NULL, 'icon_directory' => NULL, 'description' => NULL, 'attributes' => array()),
+      'function' => 'theme_file_link',
     ),
     'file_icon' => array(
       'variables' => array('file' => NULL, 'icon_directory' => NULL),
+      'function' => 'theme_file_icon',
     ),
     'file_managed_file' => array(
       'render element' => 'element',
+      'function' => 'theme_file_managed_file',
     ),
 
     // file.field.inc.
     'file_widget' => array(
       'render element' => 'element',
+      'function' => 'theme_file_widget',
     ),
     'file_widget_multiple' => array(
       'render element' => 'element',
+      'function' => 'theme_file_widget_multiple',
     ),
     'file_formatter_table' => array(
       'variables' => array('items' => NULL),
+      'function' => 'theme_file_formatter_table',
     ),
     'file_upload_help' => array(
       'variables' => array('description' => NULL, 'upload_validators' => NULL, 'cardinality' => NULL),
+      'function' => 'theme_file_upload_help',
     ),
   );
 }
diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index faca699..ee755ef 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -91,6 +91,7 @@ function forum_theme() {
     ),
     'forum_form' => array(
       'render element' => 'form',
+      'function' => 'theme_forum_form',
     ),
   );
 }
diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index 472cad4..9b23003 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -125,46 +125,56 @@ function image_theme() {
         'title' => NULL,
         'attributes' => array(),
       ),
+      'function' => 'theme_image_style',
     ),
 
     // Theme functions in image.admin.inc.
     'image_style_effects' => array(
       'render element' => 'form',
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_style_effects',
     ),
     'image_style_preview' => array(
       'variables' => array('style' => NULL),
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_style_preview',
     ),
     'image_anchor' => array(
       'render element' => 'element',
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_anchor',
     ),
     'image_resize_summary' => array(
       'variables' => array('data' => NULL),
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_resize_summary',
     ),
     'image_scale_summary' => array(
       'variables' => array('data' => NULL),
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_scale_summary',
     ),
     'image_crop_summary' => array(
       'variables' => array('data' => NULL),
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_crop_summary',
     ),
     'image_rotate_summary' => array(
       'variables' => array('data' => NULL),
       'file' => 'image.admin.inc',
+      'function' => 'theme_image_rotate_summary',
     ),
 
     // Theme functions in image.field.inc.
     'image_widget' => array(
       'render element' => 'element',
       'file' => 'image.field.inc',
+      'function' => 'theme_image_widget',
     ),
     'image_formatter' => array(
       'variables' => array('item' => NULL, 'item_attributes' => NULL, 'path' => NULL, 'image_style' => NULL),
       'file' => 'image.field.inc',
+      'function' => 'theme_image_formatter',
     ),
   );
 }
diff --git a/core/modules/language/language.module b/core/modules/language/language.module
index 4d82508..1b6a962 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -121,14 +121,17 @@ function language_theme() {
     'language_negotiation_configure_form' => array(
       'render element' => 'form',
       'file' => 'language.admin.inc',
+      'function' => 'theme_language_negotiation_configure_form',
     ),
     'language_negotiation_configure_browser_form_table' => array(
       'render element' => 'form',
       'file' => 'language.admin.inc',
+      'function' => 'theme_language_negotiation_configure_browser_form_table',
     ),
     'language_content_settings_table' => array(
       'render element' => 'element',
       'file' => 'language.admin.inc',
+      'function' => 'theme_language_content_settings_table',
     ),
   );
 }
diff --git a/core/modules/locale/locale.module b/core/modules/locale/locale.module
index 8d1e09d..ee59936 100644
--- a/core/modules/locale/locale.module
+++ b/core/modules/locale/locale.module
@@ -211,6 +211,7 @@ function locale_theme() {
     'locale_translate_edit_form_strings' => array(
       'render element' => 'form',
       'file' => 'locale.pages.inc',
+      'function' => 'theme_locale_translate_edit_form_strings',
     ),
     'locale_translation_last_check' => array(
       'variables' => array('last' => NULL),
diff --git a/core/modules/menu/menu.module b/core/modules/menu/menu.module
index e89feb8..4e51f43 100644
--- a/core/modules/menu/menu.module
+++ b/core/modules/menu/menu.module
@@ -120,6 +120,7 @@ function menu_theme() {
     'menu_overview_form' => array(
       'file' => 'menu.admin.inc',
       'render element' => 'form',
+      'function' => 'theme_menu_overview_form',
     ),
   );
 }
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index d847788..4866758 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -154,6 +154,7 @@ function node_theme() {
     ),
     'node_search_admin' => array(
       'render element' => 'form',
+      'function' => 'theme_node_search_admin',
     ),
     'node_add_list' => array(
       'variables' => array('content' => NULL),
@@ -171,6 +172,7 @@ function node_theme() {
     ),
     'field__node__title' => array(
       'base hook' => 'field',
+      'function' => 'theme_field__node__title',
     ),
   );
 }
diff --git a/core/modules/responsive_image/responsive_image.module b/core/modules/responsive_image/responsive_image.module
index 6865a81..6dd688c 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -117,6 +117,7 @@ function responsive_image_theme() {
         'attributes' => array(),
         'breakpoints' => array(),
       ),
+      'function' => 'theme_responsive_image',
     ),
     'responsive_image_formatter' => array(
       'variables' => array(
@@ -125,6 +126,7 @@ function responsive_image_theme() {
         'image_style' => NULL,
         'breakpoints' => array(),
       ),
+      'function' => 'theme_responsive_image_formatter',
     ),
     'responsive_image_source' => array(
       'variables' => array(
@@ -133,6 +135,7 @@ function responsive_image_theme() {
         'dimensions' => NULL,
         'media' => NULL,
       ),
+      'function' => 'theme_responsive_image_source',
     ),
   );
 }
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 436adc3..e20ad85 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -69,6 +69,7 @@ function simpletest_theme() {
     'simpletest_result_summary' => array(
       'render element' => 'form',
       'file' => 'simpletest.theme.inc',
+      'function' => 'theme_simpletest_result_summary',
     ),
   );
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index b746d01..a7e165b 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -172,6 +172,7 @@ function system_theme() {
     ),
     'system_config_form' => array(
       'render element' => 'form',
+      'function' => 'theme_system_config_form',
     ),
     'confirm_form' => array(
       'render element' => 'form',
@@ -180,14 +181,17 @@ function system_theme() {
     'system_modules_details' => array(
       'render element' => 'form',
       'file' => 'system.admin.inc',
+      'function' => 'theme_system_modules_details',
     ),
     'system_modules_incompatible' => array(
       'variables' => array('message' => NULL),
       'file' => 'system.admin.inc',
+      'function' => 'theme_system_modules_incompatible',
     ),
     'system_modules_uninstall' => array(
       'render element' => 'form',
       'file' => 'system.admin.inc',
+      'function' => 'theme_system_modules_uninstall',
     ),
     'status_report' => array(
       'variables' => array('requirements' => NULL),
@@ -212,9 +216,11 @@ function system_theme() {
     'system_admin_index' => array(
       'variables' => array('menu_items' => NULL),
       'file' => 'system.admin.inc',
+      'function' => 'theme_system_admin_index',
     ),
     'system_compact_link' => array(
       'variables' => array(),
+      'function' => 'theme_system_compact_link',
     ),
   ));
 }
diff --git a/core/modules/toolbar/toolbar.module b/core/modules/toolbar/toolbar.module
index 29773f1..767bf56 100644
--- a/core/modules/toolbar/toolbar.module
+++ b/core/modules/toolbar/toolbar.module
@@ -52,6 +52,7 @@ function toolbar_theme($existing, $type, $theme, $path) {
   );
   $items['toolbar_item'] = array(
     'render element' => 'element',
+    'function' => 'theme_toolbar_item',
   );
 
   return $items;