ExceptionHandler::attachListener(callable $listener) : void added

src/ExceptionHandler.php

@@ -26,6 +26,11 @@ class ExceptionHandler
      */
     protected $messageTemplate;
 
+    /**
+     * @var callable[]
+     */
+    private $listeners = [];
+
     /**
      * @param Console $console
      */
@@ -81,6 +86,8 @@ public function __invoke($exception)
         $this->console->write($message);
         $this->console->writeLine('');
 
+        $this->triggerListeners($exception);
+
         // Exceptions always indicate an error status; however, most have a
         // code of zero; set it to 1 in such cases.
         $exitCode = $exception->getCode();
@@ -166,4 +173,39 @@ private function validateException($exception)
             ));
         }
     }
+
+    /**
+     * Attach an error listener.
+     *
+     * Each listener receives one argument:
+     *
+     * - Throwable|Exception $error
+     *
+     * These instances are all immutable, and the return values of
+     * listeners are ignored; use listeners for reporting purposes
+     * only.
+     *
+     * @param callable $listener
+     * @return void
+     */
+    public function attachListener(callable $listener)
+    {
+        if (in_array($listener, $this->listeners, true)) {
+            return;
+        }
+
+        $this->listeners[] = $listener;
+    }
+
+    /**
+     * Trigger all error listeners.
+     * @param Exception|Throwable $exception
+     * @return void
+     */
+    private function triggerListeners($exception)
+    {
+        foreach ($this->listeners as $listener) {
+            $listener($exception);
+        }
+    }
 }

test/ExceptionHandlerTest.php

@@ -71,4 +71,34 @@ public function testCreateMessageFillsExpectedVariablesForExceptionWithPrevious(
         }
         $this->assertNotContains('Previous: :previous', $message);
     }
+
+    public function testErrorHandlingTriggersListeners()
+    {
+        $exception = new RuntimeException('Exception raised', 1);
+
+        $handlerCount = 0;
+
+        $listener = function ($error) use ($exception, &$handlerCount) {
+            $this->assertSame($exception, $error, 'Listener did not receive same exception as was raised');
+            ++$handlerCount;
+        };
+
+        $listener2 = clone $listener;
+
+        $this->handler->attachListener($listener);
+        $this->handler->attachListener($listener2);
+
+        $exitCode = $this->handler->__invoke($exception);
+
+        $this->assertSame(2, $handlerCount);
+    }
+
+    public function testTheSameListenerIsAttachedOnlyOnce()
+    {
+        $listener = function () {
+        };
+        $this->handler->attachListener($listener);
+        $this->handler->attachListener($listener);
+        $this->assertAttributeCount(1, 'listeners', $this->handler);
+    }
 }