Issue #3518917 by penyaskito: Invalid service alias for backend_overridable...

Issue #3518917 by penyaskito: Invalid service alias for backend_overridable services in some cases when default_backend is set

(cherry picked from commit e7207972)

core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php

@@ -37,7 +37,6 @@ class BackendCompilerPass implements CompilerPassInterface {
    * {@inheritdoc}
    */
   public function process(ContainerBuilder $container): void {
-    $driver_backend = NULL;
     if ($container->hasParameter('default_backend')) {
       $default_backend = $container->getParameter('default_backend');
       // Opt out from the default backend.
@@ -64,10 +63,10 @@ public function process(ContainerBuilder $container): void {
       if ($container->hasAlias($id)) {
         continue;
       }
-      if ($container->hasDefinition("$driver_backend.$id") || $container->hasAlias("$driver_backend.$id")) {
+      if (isset($driver_backend) && ($container->hasDefinition("$driver_backend.$id") || $container->hasAlias("$driver_backend.$id"))) {
         $container->setAlias($id, new Alias("$driver_backend.$id"));
       }
-      elseif ($container->hasDefinition("$default_backend.$id") || $container->hasAlias("$default_backend.$id")) {
+      elseif (!empty($default_backend) && ($container->hasDefinition("$default_backend.$id") || $container->hasAlias("$default_backend.$id"))) {
         $container->setAlias($id, new Alias("$default_backend.$id"));
       }
     }

core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php

@@ -4,8 +4,10 @@
 
 namespace Drupal\Tests\Core\DependencyInjection\Compiler;
 
+use Drupal\Core\Database\Connection;
 use Drupal\Core\DependencyInjection\Compiler\BackendCompilerPass;
 use Drupal\Tests\UnitTestCase;
+use PHPUnit\Framework\MockObject\MockObject;
 use Symfony\Component\DependencyInjection\Alias;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Definition;
@@ -92,6 +94,16 @@ public function testProcess(): void {
     $container->setDefinition('DriverTestMysql.service', new Definition(__NAMESPACE__ . '\\ServiceClassDriverTestMysql'));
     $this->backendPass->process($container);
     $this->assertEquals($prefix . 'DriverTestMysql', get_class($container->get('service')));
+
+    // Verify that if the container has a default_backend parameter,
+    // and there is a service named ".my-service", the right alias is created.
+    $container = $this->getMockDriverContainerWithDefaultBackendParameterArgumentAndDotPrefixedService();
+    $this->backendPass->process($container);
+
+    // Verify that if the db service returns no driver, no invalid aliases are
+    // created.
+    $container = $this->getMockDriverContainerWithNullDriverBackend();
+    $this->backendPass->process($container);
   }
 
   /**
@@ -154,6 +166,82 @@ protected function getDriverTestMysqlContainer($service) {
     return $container;
   }
 
+  /**
+   * Creates a container with a database mock definition in it.
+   *
+   * This mock won't declare a driver nor databaseType to ensure no invalid
+   * aliases are set.
+   *
+   * @return \Symfony\Component\DependencyInjection\ContainerBuilder
+   *   The container with a mock database service in it.
+   */
+  protected function getMockDriverContainerWithNullDriverBackend(): ContainerBuilder&MockObject {
+    $container = $this->getMockBuilder(ContainerBuilder::class)->getMock();
+    $mock = $this->getMockBuilder(Connection::class)->disableOriginalConstructor()->getMock();
+    $mock->expects($this->once())
+      ->method('driver')
+      ->willReturn(NULL);
+    $mock->expects($this->once())
+      ->method('databaseType')
+      ->willReturn(NULL);
+    $container->expects($this->any())
+      ->method('get')
+      ->with('database')
+      ->willReturn($mock);
+    $container->expects($this->once())
+      ->method('findTaggedServiceIds')
+      ->willReturn(['fakeService' => ['class' => 'fakeServiceClass']]);
+    $container->expects($this->never())
+      ->method('hasDefinition')
+      ->with('.fakeService')
+      ->willReturn(TRUE);
+    $container->expects($this->never())
+      ->method('setAlias');
+    return $container;
+  }
+
+  /**
+   * Creates a container with a database mock definition in it.
+   *
+   * This mock container has a default_backend parameter and a dot-prefixed
+   * service to verify the right aliases are set.
+   *
+   * @return \Symfony\Component\DependencyInjection\ContainerBuilder
+   *   The container with a mock database service in it.
+   */
+  protected function getMockDriverContainerWithDefaultBackendParameterArgumentAndDotPrefixedService(): ContainerBuilder&MockObject {
+    $container = $this->getMockBuilder(ContainerBuilder::class)->getMock();
+    $container->expects($this->once())
+      ->method('hasParameter')
+      ->with('default_backend')
+      ->willReturn(TRUE);
+    $container->expects($this->once())
+      ->method('getParameter')
+      ->with('default_backend')
+      ->willReturn('a_valid_default_backend');
+
+    $mock = $this->getMockBuilder(Connection::class)->disableOriginalConstructor()->getMock();
+    $mock->expects($this->never())
+      ->method('driver');
+    $mock->expects($this->never())
+      ->method('databaseType');
+    $container->expects($this->any())
+      ->method('get')
+      ->with('database')
+      ->willReturn($mock);
+    $container->expects($this->once())
+      ->method('findTaggedServiceIds')
+      ->willReturn(['fakeService' => ['class' => 'fakeServiceClass']]);
+    $container->expects($this->once())
+      ->method('hasDefinition')
+      ->with('a_valid_default_backend.fakeService')
+      ->willReturn(TRUE);
+    $container->expects($this->once())
+      ->method('setAlias')
+      ->with('fakeService', new Alias('a_valid_default_backend.fakeService'));
+    return $container;
+  }
+
 }
 
 /**