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>

2 files changed, 73 insertions, 0 deletions

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()));
+	}
+}