Dispatcher with optinal error handler

Tests/DispatcherTest.php

@@ -717,4 +717,69 @@ public function testRemoveSubscriber()
 		$this->assertFalse($this->instance->hasListener([$listener, 'onSomething']));
 		$this->assertFalse($this->instance->hasListener([$listener, 'onAfterSomething']));
 	}
+
+	/**
+	 * @testdox  The dispatcher should throw an error when error handler not set
+	 *
+	 * @covers   Joomla\Event\Dispatcher
+	 * @uses     Joomla\Event\DispatcherWithErrorHandlerInterface
+	 */
+	public function testDispatcherWithErrorHandlerNotSet()
+	{
+		$event = new Event('onErroredEventTest');
+
+		$this->instance->addListener('onErroredEventTest', function () {
+			throw new \RuntimeException('Event error 1');
+		});
+
+		$this->expectException(\RuntimeException::class);
+
+		$this->instance->dispatch('onErroredEventTest', $event);
+	}
+
+	/**
+	 * @testdox  The dispatchers error handler should handle an errors
+	 *
+	 * @covers   Joomla\Event\Dispatcher
+	 * @uses     Joomla\Event\DispatcherWithErrorHandlerInterface
+	 */
+	public function testDispatcherWithErrorHandlerAreSet()
+	{
+		$event  = new Event('onErroredEventTest');
+		$errors = [];
+
+		$this->instance->addListener('onErroredEventTest', function () {
+			throw new \Exception('Event error 1');
+		});
+		$this->instance->addListener('onErroredEventTest', function () {
+			// No error
+		});
+		$this->instance->addListener('onErroredEventTest', function () {
+			throw new \Exception('Event error 2');
+		});
+
+		$this->instance->setErrorHandler(function (\Throwable $e) use (&$errors) {
+			$errors[] = $e;
+		});
+
+		$this->instance->dispatch('onErroredEventTest', $event);
+
+		$this->assertEquals(2, count($errors), 'The error handler should collect correct amount of errors.');
+	}
+
+	/**
+	 * @testdox  The dispatcher should return previous Error handler when new is set
+	 *
+	 * @covers   Joomla\Event\Dispatcher
+	 * @uses     Joomla\Event\DispatcherWithErrorHandlerInterface
+	 */
+	public function testDispatcherWithErrorHandlerReturnPrevious()
+	{
+		$prev1 = $this->instance->setErrorHandler('var_dump');
+		$prev2 = $this->instance->setErrorHandler('print_r');
+		$prev3 = $this->instance->setErrorHandler(null);
+
+		$this->assertEquals([null, 'var_dump', 'print_r'], [$prev1, $prev2, $prev3], 'The dispatcher should return previous Error handler');
+	}
+
 }

src/Dispatcher.php

@@ -14,7 +14,7 @@
  *
  * @since  1.0
  */
-class Dispatcher implements DispatcherInterface
+class Dispatcher implements DispatcherInterface, DispatcherWithErrorHandlerInterface
 {
     /**
      * An array of registered events indexed by the event names.
@@ -33,6 +33,15 @@ class Dispatcher implements DispatcherInterface
      */
     protected $listeners = [];
 
+    /**
+     * Error handler.
+     *
+     * @return callable
+     *
+     * @since  __DEPLOY_VERSION__
+     */
+    protected $errorHandler;
+
     /**
      * Set an event to the dispatcher. It will replace any event with the same name.
      *
@@ -451,7 +460,11 @@ public function dispatch(string $name, ?EventInterface $event = null): EventInte
                     return $event;
                 }
 
-                $listener($event);
+                try {
+                    $listener($event);
+                } catch (\Throwable $e) {
+                    $this->handleError($e, $event);
+                }
             }
         }
 
@@ -503,4 +516,41 @@ private function getDefaultEvent(string $name): EventInterface
 
         return new Event($name);
     }
+
+    /**
+     * Set error handler for the dispatcher to handler errors in an event listeners.
+     *
+     * @param   ?callable   $handler  The error handler
+     *
+     * @return ?callable  Previous error handler
+     *
+     * @since  __DEPLOY_VERSION__
+     */
+    public function setErrorHandler(?callable $handler): ?callable
+    {
+        $previous = $this->errorHandler;
+
+        $this->errorHandler = $handler;
+
+        return $previous;
+    }
+
+    /**
+     * Handle the error. Or throw it when no handler were set.
+     *
+     * @param   \Throwable       $error  The error instance
+     * @param   EventInterface   $event  The event which were dispatched
+     *
+     * @since  __DEPLOY_VERSION__
+     *
+     * @throws \Throwable
+     */
+    protected function handleError(\Throwable $error, EventInterface $event): void
+    {
+        if (!$this->errorHandler) {
+            throw $error;
+        }
+
+        call_user_func($this->errorHandler, $error, $event);
+    }
 }

src/DispatcherWithErrorHandlerInterface.php

@@ -0,0 +1,29 @@
+<?php
+
+/**
+ * Part of the Joomla Framework Event Package
+ *
+ * @copyright  Copyright (C) 2005 - 2023 Open Source Matters, Inc. All rights reserved.
+ * @license    GNU General Public License version 2 or later; see LICENSE
+ */
+
+namespace Joomla\Event;
+
+/**
+ * Interface for dispatcher with error handler.
+ *
+ * @since  __DEPLOY_VERSION__
+ */
+interface DispatcherWithErrorHandlerInterface
+{
+    /**
+     * Set error handler for the dispatcher to handler errors in an event listeners.
+     *
+     * @param  ?callable   $handler  The error handler
+     *
+     * @return ?callable  Previous error handler
+     *
+     * @since  __DEPLOY_VERSION__
+     */
+    public function setErrorHandler(?callable $handler): ?callable;
+}