diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index d45c2e5..643e4a8 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2561,6 +2561,7 @@ 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),
@@ -2568,6 +2569,7 @@ 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),
@@ -2578,7 +2580,8 @@ 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),
@@ -2586,6 +2589,7 @@ function drupal_common_theme() {
     ),
     'indentation' => array(
       'variables' => array('size' => 1),
+      'function' => 'theme_indentation',
     ),
     // From theme.maintenance.inc.
     'maintenance_page' => array(
@@ -2598,12 +2602,15 @@ 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(
@@ -2613,22 +2620,28 @@ 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',
@@ -2648,6 +2661,7 @@ function drupal_common_theme() {
     ),
     'date' => array(
       'render element' => 'element',
+      'function' => 'theme_date',
     ),
     'checkboxes' => array(
       'render element' => 'element',
@@ -2663,6 +2677,7 @@ function drupal_common_theme() {
     ),
     'tableselect' => array(
       'render element' => 'element',
+      'function' => 'theme_tableselect',
     ),
     'form_element' => array(
       'render element' => 'element',
@@ -2670,9 +2685,11 @@ 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..c1672e2 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -426,7 +426,7 @@ 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;
+          $result[$hook]['template'] = strtr($hook, '_', '-');
         }
 
         if (isset($cache[$hook]['includes'])) {
diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index 47f2173..99ca54a 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -79,10 +79,12 @@ 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 8c52221..74a6ea7 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -57,6 +57,7 @@ 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),
@@ -65,6 +66,7 @@ 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 e68df34..0ef77d2 100644
--- a/core/modules/field_ui/field_ui.module
+++ b/core/modules/field_ui/field_ui.module
@@ -86,6 +86,7 @@ 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 9fb3c60..ef12555 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -575,26 +575,33 @@ 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 5facc3c..3f4fd23 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -92,6 +92,7 @@ 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 61b30b9..48bf873 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -111,46 +111,56 @@ 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 6a17f73..b34d131 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -98,14 +98,17 @@ 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 afb4047..5432bea 100644
--- a/core/modules/locale/locale.module
+++ b/core/modules/locale/locale.module
@@ -189,6 +189,7 @@ 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_ui/menu_ui.module b/core/modules/menu_ui/menu_ui.module
index d890237..7411cbf 100644
--- a/core/modules/menu_ui/menu_ui.module
+++ b/core/modules/menu_ui/menu_ui.module
@@ -108,6 +108,7 @@ function menu_ui_theme() {
     'menu_overview_form' => array(
       'file' => 'menu_ui.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 6b77d21..3d78cda 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -158,6 +158,7 @@ function node_theme() {
     ),
     'node_search_admin' => array(
       'render element' => 'form',
+      'function' => 'theme_node_search_admin',
     ),
     'node_add_list' => array(
       'variables' => array('content' => NULL),
@@ -175,6 +176,7 @@ 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 412dbc9..d206038 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -102,6 +102,7 @@ function responsive_image_theme() {
         'attributes' => array(),
         'breakpoints' => array(),
       ),
+      'function' => 'theme_responsive_image',
     ),
     'responsive_image_formatter' => array(
       'variables' => array(
@@ -110,6 +111,7 @@ function responsive_image_theme() {
         'image_style' => NULL,
         'breakpoints' => array(),
       ),
+      'function' => 'theme_responsive_image_formatter',
     ),
     'responsive_image_source' => array(
       'variables' => array(
@@ -118,6 +120,7 @@ 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 adc5bda..ae711af 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -55,6 +55,7 @@ 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.api.php b/core/modules/system/system.api.php
index 146fe2f..c34b240 100644
--- a/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -1111,16 +1111,20 @@ function hook_theme($existing, $type, $theme, $path) {
   return array(
     'forum_display' => array(
       'variables' => array('forums' => NULL, 'topics' => NULL, 'parents' => NULL, 'tid' => NULL, 'sortby' => NULL, 'forum_per_page' => NULL),
+      'function' => 'theme_forum_display',
     ),
     'forum_list' => array(
       'variables' => array('forums' => NULL, 'parents' => NULL, 'tid' => NULL),
+      'function' => 'theme_forum_list',
     ),
     'forum_icon' => array(
       'variables' => array('new_posts' => NULL, 'num_posts' => 0, 'comment_mode' => 0, 'sticky' => 0),
+      'function' => 'theme_forum_icon',
     ),
     'status_report' => array(
       'render element' => 'requirements',
       'file' => 'system.admin.inc',
+      'function' => 'theme_status_report',
     ),
   );
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index d719b5a..ec91444 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -160,6 +160,7 @@ function system_theme() {
     ),
     'system_config_form' => array(
       'render element' => 'form',
+      'function' => 'theme_system_config_form',
     ),
     'confirm_form' => array(
       'render element' => 'form',
@@ -168,10 +169,12 @@ function system_theme() {
     'system_modules_details' => array(
       'render element' => 'form',
       'file' => 'system.admin.inc',
+      'function' => 'theme_system_modules_details',
     ),
     'system_modules_uninstall' => array(
       'render element' => 'form',
       'file' => 'system.admin.inc',
+      'function' => 'theme_system_modules_uninstall',
     ),
     'status_report' => array(
       'variables' => array('requirements' => NULL),
@@ -196,9 +199,11 @@ 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/system/tests/modules/common_test/common_test.module b/core/modules/system/tests/modules/common_test/common_test.module
index 1a081df..2894396 100644
--- a/core/modules/system/tests/modules/common_test/common_test.module
+++ b/core/modules/system/tests/modules/common_test/common_test.module
@@ -119,6 +119,7 @@ function common_test_theme() {
     ),
     'common_test_empty' => array(
       'variables' => array('foo' => 'foo'),
+      'function' => 'theme_common_test_empty',
     ),
   );
 }
diff --git a/core/modules/system/tests/modules/theme_suggestions_test/theme_suggestions_test.module b/core/modules/system/tests/modules/theme_suggestions_test/theme_suggestions_test.module
index e963c2f..3597839 100644
--- a/core/modules/system/tests/modules/theme_suggestions_test/theme_suggestions_test.module
+++ b/core/modules/system/tests/modules/theme_suggestions_test/theme_suggestions_test.module
@@ -12,6 +12,7 @@ function theme_suggestions_test_theme() {
   $items['theme_suggestions_test_include'] = array(
     'file' => 'theme_suggestions_test.inc',
     'variables' => array(),
+    'function' => 'theme_suggestions_test_include',
   );
   return $items;
 }
diff --git a/core/modules/system/tests/modules/theme_test/theme_test.module b/core/modules/system/tests/modules/theme_test/theme_test.module
index b6f13c8..27a0136 100644
--- a/core/modules/system/tests/modules/theme_test/theme_test.module
+++ b/core/modules/system/tests/modules/theme_test/theme_test.module
@@ -7,6 +7,7 @@ function theme_test_theme($existing, $type, $theme, $path) {
   $items['theme_test'] = array(
     'file' => 'theme_test.inc',
     'variables' => array('foo' => ''),
+    'function' => 'theme_theme_test',
   );
   $items['theme_test_template_test'] = array(
     'template' => 'theme_test.template_test',
@@ -32,12 +33,15 @@ function theme_test_theme($existing, $type, $theme, $path) {
   );
   $items['theme_test_function_suggestions'] = array(
     'variables' => array(),
+    'function' => 'theme_theme_test_function_suggestions',
   );
   $items['theme_test_suggestions_include'] = array(
     'variables' => array(),
+    'function' => 'theme_theme_test_suggestions_include',
   );
   $items['theme_test_foo'] = array(
     'variables' => array('foo' => NULL),
+    'function' => 'theme_theme_test_foo',
   );
   $items['theme_test_render_element'] = array(
     'render element' => 'elements',
@@ -45,9 +49,11 @@ function theme_test_theme($existing, $type, $theme, $path) {
   );
   $items['theme_test_render_element_children'] = array(
     'render element' => 'element',
+    'function' => 'theme_theme_test_render_element_children',
   );
   $items['theme_test_function_template_override'] = array(
     'variables' => array(),
+    'function' => 'theme_theme_test_function_template_override',
   );
   $info['test_theme_not_existing_function'] = array(
     'function' => 'test_theme_not_existing_function',
diff --git a/core/modules/toolbar/toolbar.module b/core/modules/toolbar/toolbar.module
index 0f58cb2..e5c7cb9 100644
--- a/core/modules/toolbar/toolbar.module
+++ b/core/modules/toolbar/toolbar.module
@@ -53,6 +53,7 @@ function toolbar_theme($existing, $type, $theme, $path) {
   );
   $items['toolbar_item'] = array(
     'render element' => 'element',
+    'function' => 'theme_toolbar_item',
   );
 
   return $items;
diff --git a/core/modules/update/update.module b/core/modules/update/update.module
index db3b893..129087c 100644
--- a/core/modules/update/update.module
+++ b/core/modules/update/update.module
@@ -170,21 +170,26 @@ function update_theme() {
     'update_manager_update_form' => array(
       'render element' => 'form',
       'file' => 'update.manager.inc',
+      'function' => 'theme_update_manager_update_form',
     ),
     'update_last_check' => array(
       'variables' => array('last' => NULL),
+      'function' => 'theme_update_last_check',
     ),
     'update_report' => array(
       'variables' => array('data' => NULL),
       'file' => 'update.report.inc',
+      'function' => 'theme_update_report',
     ),
     'update_version' => array(
       'variables' => array('version' => NULL, 'tag' => NULL, 'class' => array()),
       'file' => 'update.report.inc',
+      'function' => 'theme_update_version',
     ),
     'update_status_label' => array(
       'variables' => array('status' => NULL),
       'file' => 'update.report.inc',
+      'function' => 'theme_update_status_label',
     ),
   );
 }
diff --git a/core/modules/user/user.module b/core/modules/user/user.module
index 9dd87e8..476eef9 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -103,12 +103,15 @@ function user_theme() {
     'user_permission_description' => array(
       'variables' => array('permission_item' => NULL, 'hide' => NULL),
       'file' => 'user.admin.inc',
+      'function' => 'theme_user_permission_description',
     ),
     'user_signature' => array(
       'variables' => array('signature' => NULL),
+      'function' => 'theme_user_signature',
     ),
     'username' => array(
       'variables' => array('account' => NULL, 'attributes' => array()),
+      'function' => 'theme_username',
     ),
   );
 }
diff --git a/core/modules/views/views.module b/core/modules/views/views.module
index 9d6e4af..4d7d70a 100644
--- a/core/modules/views/views.module
+++ b/core/modules/views/views.module
@@ -121,6 +121,7 @@ function views_theme($existing, $type, $theme, $path) {
   $hooks['views_mini_pager'] = $base + array(
     'variables' => array('tags' => array(), 'quantity' => 10, 'element' => 0, 'parameters' => array()),
     'template' => 'views-mini-pager',
+    'function' => 'theme_views_mini_pager',
   );
 
   $variables = array(
@@ -140,6 +141,7 @@ function views_theme($existing, $type, $theme, $path) {
   // Default view themes
   $hooks['views_view_field'] = $base + array(
     'variables' => array('view' => NULL, 'field' => NULL, 'row' => NULL),
+    'function' => 'theme_views_view_field',
   );
   $hooks['views_view_grouping'] = $base + array(
     'variables' => array('view' => NULL, 'grouping' => NULL, 'grouping_level' => NULL, 'rows' => NULL, 'title' => NULL),
@@ -207,6 +209,7 @@ function views_theme($existing, $type, $theme, $path) {
 
   $hooks['views_form_views_form'] = $base + array(
     'render element' => 'form',
+    'function' => 'theme_views_form_views_form',
   );
 
   $hooks['views_exposed_form'] = $base + array(
diff --git a/core/modules/views_ui/views_ui.module b/core/modules/views_ui/views_ui.module
index 951321c..abe9255 100644
--- a/core/modules/views_ui/views_ui.module
+++ b/core/modules/views_ui/views_ui.module
@@ -80,10 +80,12 @@ function views_ui_theme() {
     'views_ui_rearrange_filter_form' => array(
       'render element' => 'form',
       'file' => 'views_ui.theme.inc',
+      'function' => 'theme_views_ui_rearrange_filter_form',
     ),
     'views_ui_expose_filter_form' => array(
       'render element' => 'form',
       'file' => 'views_ui.theme.inc',
+      'function' => 'theme_views_ui_expose_filter_form',
     ),
 
     // list views
@@ -97,6 +99,7 @@ function views_ui_theme() {
     'views_ui_build_group_filter_form' => array(
       'render element' => 'form',
       'file' => 'views_ui.theme.inc',
+      'function' => 'theme_views_ui_build_group_filter_form',
     ),
 
     // On behalf of a plugin