[HttpClient] fix chaining promises returned by HttplugClient

src/Symfony/Component/HttpClient/Response/HttplugPromise.php

@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\HttpClient\Response;
 
+use function GuzzleHttp\Promise\promise_for;
 use GuzzleHttp\Promise\PromiseInterface as GuzzlePromiseInterface;
 use Http\Promise\Promise as HttplugPromiseInterface;
 use Psr\Http\Message\ResponseInterface as Psr7ResponseInterface;
@@ -31,7 +32,10 @@ final class HttplugPromise implements HttplugPromiseInterface
 
     public function then(callable $onFulfilled = null, callable $onRejected = null): self
     {
-        return new self($this->promise->then($onFulfilled, $onRejected));
+        return new self($this->promise->then(
+            $this->wrapThenCallback($onFulfilled),
+            $this->wrapThenCallback($onRejected)
+        ));
     }
 
     public function cancel(): void
@@ -62,4 +66,15 @@ final class HttplugPromise implements HttplugPromiseInterface
 
         return $result;
     }
+
+    private function wrapThenCallback(?callable $callback): ?callable
+    {
+        if (null === $callback) {
+            return null;
+        }
+
+        return static function ($value) use ($callback) {
+            return promise_for($callback($value));
+        };
+    }
 }

src/Symfony/Component/HttpClient/Tests/Response/HttplugPromiseTest.php

@@ -0,0 +1,36 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\HttpClient\Tests\Response;
+
+use GuzzleHttp\Promise\Promise;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpClient\Response\HttplugPromise;
+
+class HttplugPromiseTest extends TestCase
+{
+    public function testComplexNesting()
+    {
+        $mkPromise = function ($result): HttplugPromise {
+            $guzzlePromise = new Promise(function () use (&$guzzlePromise, $result) {
+                $guzzlePromise->resolve($result);
+            });
+
+            return new HttplugPromise($guzzlePromise);
+        };
+
+        $promise1 = $mkPromise('result');
+        $promise2 = $promise1->then($mkPromise);
+        $promise3 = $promise2->then(function ($result) { return $result; });
+
+        $this->assertSame('result', $promise3->wait());
+    }
+}