feature #31204 [Messenger] ease testing and allow forking the middlew…

…are stack (nicolas-grekas)

This PR was merged into the 4.3-dev branch.

Discussion
----------

[Messenger] ease testing and allow forking the middleware stack

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #31179
| License       | MIT
| Doc PR        | -

A less radical alternative than #31185 that preserves laziness and addresses the linked issue.

Commits
-------

3bdf4b0 [Messenger] ease testing and allow forking the middleware stack

src/Symfony/Component/Messenger/Middleware/StackInterface.php

@@ -14,6 +14,8 @@
 /**
  * @author Nicolas Grekas <p@tchwork.com>
  *
+ * Implementations must be cloneable, and each clone must unstack the stack independently.
+ *
  * @experimental in 4.2
  */
 interface StackInterface

src/Symfony/Component/Messenger/Middleware/StackMiddleware.php

@@ -20,31 +20,74 @@
  */
 class StackMiddleware implements MiddlewareInterface, StackInterface
 {
-    private $middlewareIterator;
+    private $stack;
+    private $offset = 0;
 
-    public function __construct(\Iterator $middlewareIterator = null)
+    /**
+     * @param iterable|MiddlewareInterface[]|MiddlewareInterface|null $middlewareIterator
+     */
+    public function __construct($middlewareIterator = null)
     {
-        $this->middlewareIterator = $middlewareIterator;
+        $this->stack = new MiddlewareStack();
+
+        if (null === $middlewareIterator) {
+            return;
+        }
+
+        if ($middlewareIterator instanceof \Iterator) {
+            $this->stack->iterator = $middlewareIterator;
+        } elseif ($middlewareIterator instanceof MiddlewareInterface) {
+            $this->stack->stack[] = $middlewareIterator;
+        } elseif (!\is_iterable($middlewareIterator)) {
+            throw new \TypeError(sprintf('Argument 1 passed to %s() must be iterable of %s, %s given.', __METHOD__, MiddlewareInterface::class, \is_object($middlewareIterator) ? \get_class($middlewareIterator) : \gettype($middlewareIterator)));
+        } else {
+            $this->stack->iterator = (function () use ($middlewareIterator) {
+                yield from $middlewareIterator;
+            })();
+        }
     }
 
     public function next(): MiddlewareInterface
     {
-        if (null === $iterator = $this->middlewareIterator) {
+        if (null === $next = $this->stack->next($this->offset)) {
             return $this;
         }
-        $iterator->next();
 
-        if (!$iterator->valid()) {
-            $this->middlewareIterator = null;
+        ++$this->offset;
 
-            return $this;
-        }
-
-        return $iterator->current();
+        return $next;
     }
 
     public function handle(Envelope $envelope, StackInterface $stack): Envelope
     {
         return $envelope;
     }
 }
+
+/**
+ * @internal
+ */
+class MiddlewareStack
+{
+    public $iterator;
+    public $stack = [];
+
+    public function next(int $offset): ?MiddlewareInterface
+    {
+        if (isset($this->stack[$offset])) {
+            return $this->stack[$offset];
+        }
+
+        if (null === $this->iterator) {
+            return null;
+        }
+
+        $this->iterator->next();
+
+        if (!$this->iterator->valid()) {
+            return $this->iterator = null;
+        }
+
+        return $this->stack[] = $this->iterator->current();
+    }
+}

src/Symfony/Component/Messenger/Test/Middleware/MiddlewareTestCase.php

@@ -15,6 +15,7 @@
 use Symfony\Component\Messenger\Envelope;
 use Symfony\Component\Messenger\Middleware\MiddlewareInterface;
 use Symfony\Component\Messenger\Middleware\StackInterface;
+use Symfony\Component\Messenger\Middleware\StackMiddleware;
 
 /**
  * @author Nicolas Grekas <p@tchwork.com>
@@ -25,23 +26,26 @@ abstract class MiddlewareTestCase extends TestCase
 {
     protected function getStackMock(bool $nextIsCalled = true)
     {
+        if (!$nextIsCalled) {
+            $stack = $this->createMock(StackInterface::class);
+            $stack
+                ->expects($this->never())
+                ->method('next')
+            ;
+
+            return $stack;
+        }
+
         $nextMiddleware = $this->getMockBuilder(MiddlewareInterface::class)->getMock();
         $nextMiddleware
-            ->expects($nextIsCalled ? $this->once() : $this->never())
+            ->expects($this->once())
             ->method('handle')
             ->willReturnCallback(function (Envelope $envelope, StackInterface $stack): Envelope {
                 return $envelope;
             })
         ;
 
-        $stack = $this->createMock(StackInterface::class);
-        $stack
-            ->expects($nextIsCalled ? $this->once() : $this->never())
-            ->method('next')
-            ->willReturn($nextMiddleware)
-        ;
-
-        return $stack;
+        return new StackMiddleware($nextMiddleware);
     }
 
     protected function getThrowingStackMock(\Throwable $throwable = null)
@@ -53,13 +57,6 @@ protected function getThrowingStackMock(\Throwable $throwable = null)
             ->willThrowException($throwable ?? new \RuntimeException('Thrown from next middleware.'))
         ;
 
-        $stack = $this->createMock(StackInterface::class);
-        $stack
-            ->expects($this->once())
-            ->method('next')
-            ->willReturn($nextMiddleware)
-        ;
-
-        return $stack;
+        return new StackMiddleware($nextMiddleware);
     }
 }

src/Symfony/Component/Messenger/Tests/Middleware/StackMiddlewareTest.php

@@ -0,0 +1,51 @@
+<?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\Messenger\Tests\Middleware;
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Messenger\Envelope;
+use Symfony\Component\Messenger\MessageBus;
+use Symfony\Component\Messenger\Middleware\MiddlewareInterface;
+use Symfony\Component\Messenger\Middleware\StackInterface;
+
+class StackMiddlewareTest extends TestCase
+{
+    public function testClone()
+    {
+        $middleware1 = $this->getMockBuilder(MiddlewareInterface::class)->getMock();
+        $middleware1
+            ->expects($this->once())
+            ->method('handle')
+            ->willReturnCallback(function (Envelope $envelope, StackInterface $stack): Envelope {
+                $fork = clone $stack;
+
+                $stack->next()->handle($envelope, $stack);
+                $fork->next()->handle($envelope, $fork);
+
+                return $envelope;
+            })
+        ;
+
+        $middleware2 = $this->getMockBuilder(MiddlewareInterface::class)->getMock();
+        $middleware2
+            ->expects($this->exactly(2))
+            ->method('handle')
+            ->willReturnCallback(function (Envelope $envelope, StackInterface $stack): Envelope {
+                return $envelope;
+            })
+        ;
+
+        $bus = new MessageBus([$middleware1, $middleware2]);
+
+        $bus->dispatch(new \stdClass());
+    }
+}