Callable parameter injection

This is like what we have to DI and classes, but for callables.

The motivating factor is to get rid of *service locators* in the `boot`
method of apps as a new pattern is about to emerge where we have lots of
`query` calls on the app or server container in order to fetch some
services.

With this little helper it's possible to call another (public) method
and magically have everything injected.

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

7 files changed, 187 insertions, 3 deletions

diff --git a/lib/composer/composer/autoload_classmap.php b/lib/composer/composer/autoload_classmap.php
index 9d1ebf2815b..1fa17bab000 100644
--- a/lib/composer/composer/autoload_classmap.php
+++ b/lib/composer/composer/autoload_classmap.php
@@ -548,6 +548,7 @@ return array(
     'OC\\AppFramework\\App' => $baseDir . '/lib/private/AppFramework/App.php',
     'OC\\AppFramework\\Bootstrap\\BootContext' => $baseDir . '/lib/private/AppFramework/Bootstrap/BootContext.php',
     'OC\\AppFramework\\Bootstrap\\Coordinator' => $baseDir . '/lib/private/AppFramework/Bootstrap/Coordinator.php',
+    'OC\\AppFramework\\Bootstrap\\FunctionInjector' => $baseDir . '/lib/private/AppFramework/Bootstrap/FunctionInjector.php',
     'OC\\AppFramework\\Bootstrap\\RegistrationContext' => $baseDir . '/lib/private/AppFramework/Bootstrap/RegistrationContext.php',
     'OC\\AppFramework\\DependencyInjection\\DIContainer' => $baseDir . '/lib/private/AppFramework/DependencyInjection/DIContainer.php',
     'OC\\AppFramework\\Http' => $baseDir . '/lib/private/AppFramework/Http.php',
diff --git a/lib/composer/composer/autoload_static.php b/lib/composer/composer/autoload_static.php
index 1b7cf1fa13a..82ebb9eef05 100644
--- a/lib/composer/composer/autoload_static.php
+++ b/lib/composer/composer/autoload_static.php
@@ -577,6 +577,7 @@ class ComposerStaticInit53792487c5a8370acc0b06b1a864ff4c
         'OC\\AppFramework\\App' => __DIR__ . '/../../..' . '/lib/private/AppFramework/App.php',
         'OC\\AppFramework\\Bootstrap\\BootContext' => __DIR__ . '/../../..' . '/lib/private/AppFramework/Bootstrap/BootContext.php',
         'OC\\AppFramework\\Bootstrap\\Coordinator' => __DIR__ . '/../../..' . '/lib/private/AppFramework/Bootstrap/Coordinator.php',
+        'OC\\AppFramework\\Bootstrap\\FunctionInjector' => __DIR__ . '/../../..' . '/lib/private/AppFramework/Bootstrap/FunctionInjector.php',
         'OC\\AppFramework\\Bootstrap\\RegistrationContext' => __DIR__ . '/../../..' . '/lib/private/AppFramework/Bootstrap/RegistrationContext.php',
         'OC\\AppFramework\\DependencyInjection\\DIContainer' => __DIR__ . '/../../..' . '/lib/private/AppFramework/DependencyInjection/DIContainer.php',
         'OC\\AppFramework\\Http' => __DIR__ . '/../../..' . '/lib/private/AppFramework/Http.php',
diff --git a/lib/private/AppFramework/Bootstrap/BootContext.php b/lib/private/AppFramework/Bootstrap/BootContext.php
index 3831fe4e396..d206884c0b7 100644
--- a/lib/private/AppFramework/Bootstrap/BootContext.php
+++ b/lib/private/AppFramework/Bootstrap/BootContext.php
@@ -45,4 +45,8 @@ class BootContext implements IBootContext {
 	public function getServerContainer(): IServerContainer {
 		return $this->appContainer->getServer();
 	}
+
+	public function injectFn(callable $fn) {
+		return (new FunctionInjector($this->appContainer))->injectFn($fn);
+	}
 }
diff --git a/lib/private/AppFramework/Bootstrap/FunctionInjector.php b/lib/private/AppFramework/Bootstrap/FunctionInjector.php
new file mode 100644
index 00000000000..cb1dc7d3f37
--- /dev/null
+++ b/lib/private/AppFramework/Bootstrap/FunctionInjector.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2020 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2020 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace OC\AppFramework\Bootstrap;
+
+use Closure;
+use OCP\AppFramework\QueryException;
+use OCP\IContainer;
+use ReflectionFunction;
+use ReflectionParameter;
+use function array_map;
+
+class FunctionInjector {
+
+	/** @var IContainer */
+	private $container;
+
+	public function __construct(IContainer $container) {
+		$this->container = $container;
+	}
+
+	public function injectFn(callable $fn) {
+		$reflected = new ReflectionFunction(Closure::fromCallable($fn));
+		return $fn(...array_map(function (ReflectionParameter $param) {
+			// First we try by type (more likely these days)
+			if (($type = $param->getType()) !== null) {
+				try {
+					return $this->container->query($type->getName());
+				} catch (QueryException $ex) {
+					// Ignore and try name as well
+				}
+			}
+			// Second we try by name (mostly for primitives)
+			try {
+				return $this->container->query($param->getName());
+			} catch (QueryException $ex) {
+				// As a last resort we pass `null` if allowed
+				if ($type !== null && $type->allowsNull()) {
+					return null;
+				}
+
+				// Nothing worked, time to bail out
+				throw $ex;
+			}
+		}, $reflected->getParameters()));
+	}
+}
diff --git a/lib/public/AppFramework/Bootstrap/IBootContext.php b/lib/public/AppFramework/Bootstrap/IBootContext.php
index 6ceec5d2fcb..47b26528c66 100644
--- a/lib/public/AppFramework/Bootstrap/IBootContext.php
+++ b/lib/public/AppFramework/Bootstrap/IBootContext.php
@@ -26,7 +26,9 @@ declare(strict_types=1);
 namespace OCP\AppFramework\Bootstrap;
 
 use OCP\AppFramework\IAppContainer;
+use OCP\AppFramework\QueryException;
 use OCP\IServerContainer;
+use Throwable;
 
 /**
  * @since 20.0.0
@@ -52,4 +54,24 @@ interface IBootContext {
 	 * @since 20.0.0
 	 */
 	public function getServerContainer(): IServerContainer;
+
+	/**
+	 * Invoke the given callable and inject all parameters based on their types
+	 * and names
+	 *
+	 * Note: when used with methods, make sure they are public or use \Closure::fromCallable
+	 * to wrap the private method call, e.g.
+	 *  * `$context->injectFn([$obj, 'publicMethod'])`
+	 *  * `$context->injectFn([$this, 'publicMethod'])`
+	 *  * `$context->injectFn(\Closure::fromCallable([$this, 'privateMethod']))`
+	 *
+	 * Note: the app container will be queried
+	 *
+	 * @param callable $fn
+	 * @throws QueryException if at least one of the parameter can't be resolved
+	 * @throws Throwable any error the function invocation might cause
+	 * @return mixed|null the return value of the invoked function, if any
+	 * @since 20.0.0
+	 */
+	public function injectFn(callable $fn);
 }
diff --git a/tests/lib/AppFramework/Bootstrap/FunctionInjectorTest.php b/tests/lib/AppFramework/Bootstrap/FunctionInjectorTest.php
new file mode 100644
index 00000000000..cd2332b0588
--- /dev/null
+++ b/tests/lib/AppFramework/Bootstrap/FunctionInjectorTest.php
@@ -0,0 +1,84 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2020 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2020 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace lib\AppFramework\Bootstrap;
+
+use OC\AppFramework\Bootstrap\FunctionInjector;
+use OC\AppFramework\Utility\SimpleContainer;
+use Test\TestCase;
+
+interface Foo {
+}
+
+class FunctionInjectorTest extends TestCase {
+
+	/** @var SimpleContainer */
+	private $container;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->container = new SimpleContainer();
+	}
+
+	public function testInjectFnNotRegistered(): void {
+		$this->expectException(\OCP\AppFramework\QueryException::class);
+
+		(new FunctionInjector($this->container))->injectFn(static function (Foo $p1): void {
+		});
+	}
+
+	public function testInjectFnNotRegisteredButNullable(): void {
+		(new FunctionInjector($this->container))->injectFn(static function (?Foo $p1): void {
+		});
+
+		// Nothing to assert. No errors means everything is fine.
+		$this->addToAssertionCount(1);
+	}
+
+	public function testInjectFnByType(): void {
+		$this->container->registerService(Foo::class, function () {
+			$this->addToAssertionCount(1);
+			return new class implements Foo {
+			};
+		});
+
+		(new FunctionInjector($this->container))->injectFn(static function (Foo $p1): void {
+		});
+
+		// Nothing to assert. No errors means everything is fine.
+		$this->addToAssertionCount(1);
+	}
+
+	public function testInjectFnByName(): void {
+		$this->container->registerParameter('test', 'abc');
+
+		(new FunctionInjector($this->container))->injectFn(static function ($test): void {
+		});
+
+		// Nothing to assert. No errors means everything is fine.
+		$this->addToAssertionCount(1);
+	}
+}
diff --git a/tests/lib/AppFramework/Utility/SimpleContainerTest.php b/tests/lib/AppFramework/Utility/SimpleContainerTest.php
index f8a43058305..36fa1febfcf 100644
--- a/tests/lib/AppFramework/Utility/SimpleContainerTest.php
+++ b/tests/lib/AppFramework/Utility/SimpleContainerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * ownCloud - App Framework
  *
@@ -67,13 +69,14 @@ class SimpleContainerTest extends \Test\TestCase {
 	}
 
 
+
 	public function testRegister() {
 		$this->container->registerParameter('test', 'abc');
 		$this->assertEquals('abc', $this->container->query('test'));
 	}
 
 
-	
+
 	public function testNothingRegistered() {
 		$this->expectException(\OCP\AppFramework\QueryException::class);
 
@@ -81,7 +84,7 @@ class SimpleContainerTest extends \Test\TestCase {
 	}
 
 
-	
+
 	public function testNotAClass() {
 		$this->expectException(\OCP\AppFramework\QueryException::class);
 
@@ -190,7 +193,7 @@ class SimpleContainerTest extends \Test\TestCase {
 		$this->assertEquals('abc', $this->container->query($query));
 	}
 
-	
+
 	public function testConstructorComplexNoTestParameterFound() {
 		$this->expectException(\OCP\AppFramework\QueryException::class);