Fixed Promise<null> calling rejection handler given after being successfully resolved

closes #6110

this is a weird use case, but it should work nonetheless.

src/promise/Promise.php

@@ -41,8 +41,11 @@ final class Promise{
 	 * @phpstan-param \Closure() : void $onFailure
 	 */
 	public function onCompletion(\Closure $onSuccess, \Closure $onFailure) : void{
-		if($this->shared->resolved){
+		$state = $this->shared->state;
-			$this->shared->result === null ? $onFailure() : $onSuccess($this->shared->result);
+		if($state === true){
+			$onSuccess($this->shared->result);
+		}elseif($state === false){
+			$onFailure();
 		}else{
 			$this->shared->onSuccess[spl_object_id($onSuccess)] = $onSuccess;
 			$this->shared->onFailure[spl_object_id($onFailure)] = $onFailure;
@@ -50,6 +53,8 @@ final class Promise{
 	}
 
 	public function isResolved() : bool{
-		return $this->shared->resolved;
+		//TODO: perhaps this should return true when rejected? currently there's no way to tell if a promise was
+		//rejected or just hasn't been resolved yet
+		return $this->shared->state === true;
 	}
 }

src/promise/PromiseResolver.php

@@ -41,10 +41,10 @@ final class PromiseResolver{
 	 * @phpstan-param TValue $value
 	 */
 	public function resolve(mixed $value) : void{
-		if($this->shared->resolved){
+		if($this->shared->state !== null){
 			throw new \LogicException("Promise has already been resolved/rejected");
 		}
-		$this->shared->resolved = true;
+		$this->shared->state = true;
 		$this->shared->result = $value;
 		foreach($this->shared->onSuccess as $c){
 			$c($value);
@@ -54,10 +54,10 @@ final class PromiseResolver{
 	}
 
 	public function reject() : void{
-		if($this->shared->resolved){
+		if($this->shared->state !== null){
 			throw new \LogicException("Promise has already been resolved/rejected");
 		}
-		$this->shared->resolved = true;
+		$this->shared->state = false;
 		foreach($this->shared->onFailure as $c){
 			$c();
 		}

src/promise/PromiseSharedData.php

@@ -41,8 +41,8 @@ final class PromiseSharedData{
 	 */
 	public array $onFailure = [];
 
-	public bool $resolved = false;
+	public ?bool $state = null;
 
-	/** @phpstan-var TValue|null */
+	/** @phpstan-var TValue */
-	public mixed $result = null;
+	public mixed $result;
 }

tests/phpunit/promise/PromiseTest.php

@@ -0,0 +1,42 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+ */
+
+declare(strict_types=1);
+
+namespace pocketmine\promise;
+
+use PHPUnit\Framework\TestCase;
+
+final class PromiseTest extends TestCase{
+
+	public function testPromiseNull() : void{
+		$resolver = new PromiseResolver();
+		$resolver->resolve(null);
+		$resolver->getPromise()->onCompletion(
+			function(mixed $value) : void{
+				self::assertNull($value);
+			},
+			function() : void{
+				self::fail("Promise should not be rejected");
+			}
+		);
+	}
+}