Log to custom callback

.gitattributes

@@ -3,5 +3,6 @@
 .gitattributes export-ignore
 .gitignore export-ignore
 .php_cs export-ignore
+Makefile export-ignore
 phpstan.neon export-ignore
 phpunit.xml export-ignore

lib/ErrorHandler.php

@@ -55,6 +55,11 @@ final class ErrorHandler
      */
     private $emailCallback;
 
+    /**
+     * @var callable
+     */
+    private $errorLogCallback = '\\error_log';
+
     /**
      * @var array<int, bool>
      */
@@ -99,6 +104,16 @@ public function __construct(callable $emailCallback)
         $this->emailCallback = $emailCallback;
     }
 
+    public function setErrorLogCallback(callable $callback): void
+    {
+        $this->errorLogCallback = $callback;
+    }
+
+    public function getErrorLogCallback(): callable
+    {
+        return $this->errorLogCallback;
+    }
+
     public function setAutoExit(bool $autoExit): void
     {
         $this->autoExit = $autoExit;
@@ -365,6 +380,8 @@ public function logException(Throwable $exception): void
             return;
         }
 
+        $errorLogCallback = $this->errorLogCallback;
+
         $i = 0;
         do {
             $output = \sprintf('%s%s: %s in %s:%s%s%s',
@@ -377,7 +394,7 @@ public function logException(Throwable $exception): void
                 $this->purgeTrace($exception->getTraceAsString())
             );
 
-            \error_log($output);
+            $errorLogCallback($output);
 
             ++$i;
         } while ($exception = $exception->getPrevious());

tests/ErrorHandlerTest.php

@@ -306,4 +306,24 @@ public function test404SpecificExceptionForHeaders(): void
 
         self::assertStringContainsString('404: Not Found', $this->errorHandler->renderHtmlException(new RuntimeException()));
     }
+
+    public function testCanSetCustomErrorLogCallback(): void
+    {
+        $this->errorHandler->setLogErrors(true);
+        self::assertSame('\\error_log', $this->errorHandler->getErrorLogCallback());
+
+        $data           = [];
+        $customCallback = static function (string $text) use (& $data): void {
+            $data[] = $text;
+        };
+
+        $this->errorHandler->setErrorLogCallback($customCallback);
+
+        self::assertSame($customCallback, $this->errorHandler->getErrorLogCallback());
+
+        $this->errorHandler->logException($this->exception);
+
+        self::assertSame(0, \filesize($this->errorLog));
+        self::assertStringContainsString($this->exception->getMessage(), \var_export($data, true));
+    }
 }