The ServiceListener needs to be able to overwrite existing configuration

In testing zend-mvc for forwards compatibility, I ran into an issue with
the ServiceListener: if a service was already configured when the
ServiceListener ran, an exception was thrown due to being unable to
overwrite services. This should always be allowed in the
ServiceListener.

src/Listener/ServiceListener.php

@@ -217,7 +217,15 @@ public function onLoadModulesPost(ModuleEvent $e)
             }
 
             $serviceConfig = new ServiceConfig($smConfig);
+
+            // The service listener is meant to operate during bootstrap, and, as such,
+            // needs to be able to override existing configuration.
+            $allowOverride = $sm['service_manager']->getAllowOverride();
+            $sm['service_manager']->setAllowOverride(true);
+
             $serviceConfig->configureServiceManager($sm['service_manager']);
+
+            $sm['service_manager']->setAllowOverride($allowOverride);
         }
     }
 

test/Listener/ServiceListenerTest.php

@@ -358,4 +358,44 @@ public function testCanDetachListeners(array $dependencies)
         $listeners = $this->getArrayOfListenersForEvent(ModuleEvent::EVENT_LOAD_MODULES_POST, $events);
         $this->assertCount(0, $listeners);
     }
+
+    public function testListenerCanOverrideServicesInServiceManagers()
+    {
+        $services = new ServiceManager();
+        $services->setService('config', []);
+        $services->setFactory('foo', function ($services) {
+            return $services;
+        });
+        $listener = new ServiceListener($services);
+        $listener->addServiceManager(
+            $services,
+            'service_manager',
+            ServiceProviderInterface::class,
+            'getServiceConfig'
+        );
+
+        $module = new TestAsset\ServiceProviderModule([
+            'services' => [
+                'config' => [ 'foo' => 'bar'],
+            ],
+            'factories' => [
+                'foo' => function ($services) {
+                    return new stdClass();
+                },
+            ],
+        ]);
+
+        $event          = new ModuleEvent();
+        $configListener = new ConfigListener();
+        $event->setConfigListener($configListener);
+
+        $event->setModule($module);
+        $listener->onLoadModule($event);
+        $listener->onLoadModulesPost($event);
+
+        $this->assertTrue($services->has('config'));
+        $this->assertTrue($services->has('foo'));
+        $this->assertEquals(['foo' => 'bar'], $services->get('config'), 'Config service was not overridden');
+        $this->assertInstanceOf(stdClass::class, $services->get('foo'), 'Foo service was not overridden');
+    }
 }