Issue #3144354 by alexpott, vijaycs85, andypost: ModuleInstaller loads .module...

Issue #3144354 by alexpott, vijaycs85, andypost: ModuleInstaller loads .module and .install before allowing classes to autoloaded

core/lib/Drupal/Core/Extension/ModuleInstaller.php

@@ -193,14 +193,9 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
           }
         }
 
-        // Update the module handler in order to load the module's code.
-        // This allows the module to participate in hooks and its existence to
-        // be discovered by other modules.
-        // The current ModuleHandler instance is obsolete with the kernel
-        // rebuild below.
+        // Update the module handler in order to have the correct module list
+        // for the kernel update.
         $this->moduleHandler->setModuleList($module_filenames);
-        $this->moduleHandler->load($module);
-        module_load_install($module);
 
         // Clear the static cache of the "extension.list.module" service to pick
         // up the new module, since it merges the installation status of modules
@@ -210,6 +205,10 @@ public function install(array $module_list, $enable_dependencies = TRUE) {
         // Update the kernel to include it.
         $this->updateKernel($module_filenames);
 
+        // Load the module's .module and .install files.
+        $this->moduleHandler->load($module);
+        module_load_install($module);
+
         // Replace the route provider service with a version that will rebuild
         // if routes used during installation. This ensures that a module's
         // routes are available during installation. This has to occur before

core/modules/system/tests/modules/module_autoload_test/module_autoload_test.module

+<?php
+
+/**
+ * @file
+ * Test module.
+ */
+
+use Drupal\module_autoload_test\SomeClass;
+
+define('MODULE_AUTOLOAD_TEST_CONSTANT', SomeClass::TEST);

core/modules/system/tests/modules/module_autoload_test/src/SomeClass.php

@@ -4,6 +4,8 @@
 
 class SomeClass {
 
+  const TEST = '\Drupal\module_autoload_test\SomeClass::TEST';
+
   public function testMethod() {
     return 'Drupal\\module_autoload_test\\SomeClass::testMethod() was invoked.';
   }

core/modules/system/tests/src/Functional/Module/ClassLoaderTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\system\Functional\Module;
 
+use Drupal\module_autoload_test\SomeClass;
 use Drupal\Tests\BrowserTestBase;
 
 /**
@@ -96,4 +97,19 @@ public function testMultipleModules() {
     $this->assertTrue(\Drupal::moduleHandler()->moduleExists('module_install_class_loader_test2'), 'The module_install_class_loader_test2 module has been installed.');
   }
 
+  /**
+   * Tests that .module files can use class constants in main section.
+   */
+  public function testAutoloadFromModuleFile() {
+    $this->assertFalse(defined('MODULE_AUTOLOAD_TEST_CONSTANT'));
+    $this->drupalLogin($this->rootUser);
+    $edit = [
+      "modules[module_autoload_test][enable]" => TRUE,
+    ];
+    $this->drupalPostForm('admin/modules', $edit, t('Install'));
+    $this->assertSession()->statusCodeEquals(200);
+    $this->resetAll();
+    $this->assertSame(SomeClass::TEST, MODULE_AUTOLOAD_TEST_CONSTANT);
+  }
+
 }