feat(dependencyinjection): Allow optional (nullable) services

Allows working with classes that might or might not be available.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

lib/private/AppFramework/Utility/SimpleContainer.php

@@ -105,6 +105,11 @@ class SimpleContainer implements ArrayAccess, ContainerInterface, IContainer {
 					try {
 						return $this->query($resolveName);
 					} catch (QueryException $e2) {
+						// Pass null if typed and nullable
+						if ($parameter->allowsNull() && ($parameterType instanceof ReflectionNamedType)) {
+							return null;
+						}
+
 						// don't lose the error we got while trying to query by type
 						throw new QueryException($e->getMessage(), (int) $e->getCode(), $e);
 					}

tests/lib/AppFramework/Utility/SimpleContainerTest.php

@@ -50,6 +50,17 @@ class ClassComplexConstructor {
 	}
 }
 
+class ClassNullableUntypedConstructorArg {
+	public function __construct($class) {
+	}
+}
+class ClassNullableTypedConstructorArg {
+	public $class;
+	public function __construct(?\Some\Class $class) {
+		$this->class = $class;
+	}
+}
+
 interface IInterfaceConstructor {
 }
 class ClassInterfaceConstructor {
@@ -243,4 +254,17 @@ class SimpleContainerTest extends \Test\TestCase {
 		$this->assertNotSame(
 			$this->container->query('test'), $this->container->query('test1'));
 	}
+
+	public function testQueryUntypedNullable(): void {
+		$this->expectException(\OCP\AppFramework\QueryException::class);
+
+		$this->container->query(ClassNullableUntypedConstructorArg::class);
+	}
+
+	public function testQueryTypedNullable(): void {
+		/** @var ClassNullableTypedConstructorArg $service */
+		$service = $this->container->query(ClassNullableTypedConstructorArg::class);
+
+		self::assertNull($service->class);
+	}
 }