Use register_shutdown_function for panic

src/Promise/ErrorHandler.php

@@ -112,28 +112,14 @@ private static function triggerErrorHandler($message, $error) {
     private static function panic($error) {
         // The set error handler did throw or not exist, PHP's error handler threw, no chance to handle the error
         // gracefully at this time. PANIC!
-
-        // Print error information to STDERR so the reason for the program abortion can be found, but do not expose
-        // exception message and trace, as they might contain sensitive information and we do not know whether STDERR
-        // might be available to an untrusted user.
-
         // Exit with the same code as if PHP exits because of an uncaught exception.
+        $message = "'%s' thrown while trying to report a throwing AsyncInterop\\Promise::when() handler gracefully.";
+        $exception = new \Exception(\sprintf($message, \get_class($error)), 0, $error);
 
-        try {
-            // fputs might fail due to a closed pipe
-            // no STDERR, because it doesn't exist on piped STDIN
-            // no finally, because PHP 5.4
-            \fputs(\fopen("php://stderr", "w"), \sprintf(
-                "Fatal error: Uncaught exception '%s' while trying to report a throwing AsyncInterop\\Promise::when()"
-                . " handler gracefully." . \PHP_EOL,
-                \get_class($error)
-            ));
+        \register_shutdown_function(function () use ($exception) {
+            throw $exception;
+        });
 
-            exit(255);
-        } catch (\Exception $e) {
-            exit(255);
-        } catch (\Throwable $e) {
-            exit(255);
-        }
+        exit(255);
     }
 }

test/phpt/error_handler_007.phpt

@@ -30,5 +30,17 @@ set_error_handler(function () {
 AsyncInterop\Promise\ErrorHandler::notify(new Exception);
 
 ?>
---EXPECT--
-Fatal error: Uncaught exception 'RuntimeException' while trying to report a throwing AsyncInterop\Promise::when() handler gracefully.
+--EXPECTF--
+%SRuntimeException%S
+Stack trace:
+#0 %s
+#1 %s
+#2 %s
+#3 %s
+#4 %s
+
+Next %sxception%s
+Stack trace:
+#0 %s
+#1 %s
+#2 %s