Issue #2494989 by catch, alexpott, vijaycs85: Don't render main help pages on...

Issue #2494989 by catch, alexpott, vijaycs85: Don't render main help pages on modules page just to generate help links - can lead to high memory usage on form submit

core/modules/help/help.api.php

@@ -22,7 +22,8 @@
  * Help block (provided by the core Help module), if the block is displayed on
  * that page. The module overview help information is displayed by the Help
  * module. It can be accessed from the page at admin/help or from the Extend
- * Extend page.
+ * Extend page. If a module implements hook_help() the help system expects
+ * module overview help to be provided.
  *
  * For detailed usage examples of:
  * - Module overview help, see content_translation_help(). Module overview

core/modules/help/src/Controller/HelpController.php

@@ -68,9 +68,7 @@ public function helpMain() {
   protected function helpLinksAsList() {
     $modules = array();
     foreach ($this->moduleHandler()->getImplementations('help') as $module) {
-      if ($this->moduleHandler()->invoke($module, 'help', array("help.page.$module", $this->routeMatch))) {
-        $modules[$module] = $this->moduleHandler->getName($module);
-      }
+      $modules[$module] = $this->moduleHandler->getName($module);
     }
     asort($modules);
 

core/modules/help/src/Tests/HelpTest.php

@@ -19,11 +19,16 @@ class HelpTest extends WebTestBase {
   /**
    * Modules to enable.
    *
+   * The help_test module implements hook_help() but does not provide a module
+   * overview page.
+   *
    * @var array.
    */
-  public static $modules = array('shortcut');
+  public static $modules = array('help_test');
 
-  // Tests help implementations of many arbitrary core modules.
+  /**
+   * Use the Standard profile to test help implementations of many core modules.
+   */
   protected $profile = 'standard';
 
   /**
@@ -71,6 +76,11 @@ public function testHelp() {
     foreach ($this->getModuleList() as $module => $name) {
       $this->assertLink($name, 0, format_string('Link properly added to @name (admin/help/@module)', array('@module' => $module, '@name' => $name)));
     }
+
+    // Ensure that module which does not provide an module overview page is
+    // handled correctly.
+    $this->clickLink(\Drupal::moduleHandler()->getName('help_test'));
+    $this->assertRaw(t('No help is available for module %module.', array('%module' => \Drupal::moduleHandler()->getName('help_test'))));
   }
 
   /**

core/modules/help/src/Tests/NoHelpTest.php

@@ -44,6 +44,10 @@ public function testMainPageNoHelp() {
     $this->drupalGet('admin/help');
     $this->assertResponse(200);
     $this->assertText('Help is available on the following items', 'Help page is found.');
-    $this->assertNoText('Hook menu tests', 'Making sure the test module menu_test does not display a help link on admin/help.');
+    $this->assertFalse(\Drupal::moduleHandler()->implementsHook('menu_test', 'help'), 'The menu_test module does not implement hook_help');
+    $this->assertNoText(\Drupal::moduleHandler()->getName('menu_test'), 'Making sure the test module menu_test does not display a help link on admin/help.');
+
+    $this->drupalGet('admin/help/menu_test');
+    $this->assertResponse(404, 'Getting a module overview help page for a module that does not implement hook_help() results in a 404.');
   }
 }

core/modules/help/tests/modules/help_test/help_test.module

+<?php
+
+/**
+ * @file
+ * Test Help module.
+ */
+
+use \Drupal\Core\Routing\RouteMatchInterface;
+
+/**
+ * Implements hook_help().
+ */
+function help_test_help($route_name, RouteMatchInterface $route_match) {
+  // Do not implement a module overview page to test an empty implementation.
+  // @see \Drupal\help\Tests\HelpTest
+}

core/modules/system/src/Form/ModulesListForm.php

@@ -255,17 +255,17 @@ protected function buildRow(array $modules, Extension $module, $distribution) {
     $row['description']['#markup'] = $this->t($module->info['description']);
     $row['version']['#markup'] = $module->info['version'];
 
-    // Generate link for module's help page, if there is one.
+    // Generate link for module's help page. Assume that if a hook_help()
+    // implementation exists then the module provides an overview page, rather
+    // than checking to see if the page exists, which is costly.
     $row['links']['help'] = array();
     if ($this->moduleHandler->moduleExists('help') && $module->status && in_array($module->getName(), $this->moduleHandler->getImplementations('help'))) {
-      if ($this->moduleHandler->invoke($module->getName(), 'help', array('help.page.' . $module->getName(), $this->routeMatch))) {
-        $row['links']['help'] = array(
-          '#type' => 'link',
-          '#title' => $this->t('Help'),
-          '#url' => Url::fromRoute('help.page', ['name' => $module->getName()]),
-          '#options' => array('attributes' => array('class' =>  array('module-link', 'module-link-help'), 'title' => $this->t('Help'))),
-        );
-      }
+      $row['links']['help'] = array(
+        '#type' => 'link',
+        '#title' => $this->t('Help'),
+        '#url' => Url::fromRoute('help.page', ['name' => $module->getName()]),
+        '#options' => array('attributes' => array('class' =>  array('module-link', 'module-link-help'), 'title' => $this->t('Help'))),
+      );
     }
 
     // Generate link for module's permission, if the user has access to it.