fix: Adapt yield from statements to work in PHP 5.6

`yield from` was introduced in PHP 7. As such, to work in PHP 5.6, we
need to modify the statements to iterate over the inner generator and
yield results directly.

Author: weierophinney

src/EventManager.php

@@ -383,13 +383,17 @@ public function clearListeners($eventName)
 
     /**
      * {@inheritDoc}
+     * @todo Use `yield from` once we bump the minimum supported PHP version to 7+.
      * @deprecated This method will be removed in version 4.0, and EventManager
      *     will no longer be its own listener provider; use external listener
      *     providers and the createUsingListenerProvider method instead.
      */
     public function getListenersForEvent($event)
     {
-        yield from $this->provider->getListenersForEvent($event, $this->identifiers);
+        // @todo Use `yield from $this->provider->getListenersForEvent(...)
+        foreach ($this->provider->getListenersForEvent($event, $this->identifiers) as $listener) {
+            yield $listener;
+        }
     }
 
     /**

src/ListenerProvider/PrioritizedAggregateListenerProvider.php

@@ -30,17 +30,24 @@ public function __construct(array $providers, ListenerProviderInterface $default
 
     /**
      * {@inheritDoc}
+     * @todo  Use `yield from` once we bump the minimum supported PHP version to 7+.
      * @param string[] $identifiers Any identifiers to use when retrieving
      *     listeners from child providers.
      */
     public function getListenersForEvent($event, array $identifiers = [])
     {
-        yield from $this->iterateByPriority(
-            $this->getListenersForEventByPriority($event, $identifiers)
-        );
+        // @todo `yield from $this->iterateByPriority(...)`
+        foreach ($this->iterateByPriority($this->getListenersForEventByPriority($event, $identifiers)) as $listener) {
+            yield $listener;
+        }
+
+        if (! $this->default) {
+            return;
+        }
 
-        if ($this->default) {
-            yield from $this->default->getListenersForEvent($event, $identifiers);
+        // @todo `yield from $this->default->getListenersForEvent(...)`
+        foreach ($this->default->getListenersForEvent($event, $identifiers) as $listener) {
+            yield $listener;
         }
     }
 
@@ -79,14 +86,18 @@ private function validateProviders(array $providers)
     }
 
     /**
+     * @todo   Use `yield from` once we bump the minimum supported PHP version to 7+.
      * @param  array $prioritizedListeners
      * @return iterable
      */
     private function iterateByPriority($prioritizedListeners)
     {
         krsort($prioritizedListeners);
         foreach ($prioritizedListeners as $listeners) {
-            yield from $listeners;
+            // @todo `yield from $listeners`
+            foreach ($listeners as $listener) {
+                yield $listener;
+            }
         }
     }
 }

src/ListenerProvider/PrioritizedIdentifierListenerProvider.php

@@ -30,15 +30,17 @@ class PrioritizedIdentifierListenerProvider implements
 
     /**
      * {@inheritDoc}
+     * @todo   Use `yield from` once we bump the minimum supported PHP version to 7+.
      * @param  array $identifiers Identifiers from which to match event listeners.
      * @throws Exception\InvalidArgumentException for invalid event types
      * @throws Exception\InvalidArgumentException for invalid identifier types
      */
     public function getListenersForEvent($event, array $identifiers = [])
     {
-        yield from $this->iterateByPriority(
-            $this->getListenersForEventByPriority($event, $identifiers)
-        );
+        // @todo `yield from $this->iterateByPriority(...)`
+        foreach ($this->iterateByPriority($this->getListenersForEventByPriority($event, $identifiers)) as $listener) {
+            yield $listener;
+        }
     }
 
     /**
@@ -265,14 +267,18 @@ private function getEventList($event)
     }
 
     /**
+     * @todo   Use `yield from` once we bump the minimum supported PHP version to 7+.
      * @param  array $prioritizedListeners
      * @return iterable
      */
     private function iterateByPriority($prioritizedListeners)
     {
         krsort($prioritizedListeners);
         foreach ($prioritizedListeners as $listeners) {
-            yield from $listeners;
+            // @todo `yield from $listeners`
+            foreach ($listeners as $listener) {
+                yield $listener;
+            }
         }
     }
 }

src/SharedEventManager/SharedEventManagerDecorator.php

@@ -27,12 +27,12 @@ public function __construct(SharedEventManagerInterface $proxy)
 
     /**
      * {@inheritDoc}
-     * @var array $identifiers Identifiers provided by dispatcher, if any.
+     * @var iterable $identifiers Identifiers provided by dispatcher, if any.
      *     This argument is deprecated, and will be removed in version 4.
      */
     public function getListenersForEvent($event, array $identifiers = [])
     {
-        yield from $this->getListeners($identifiers, $this->getEventName($event, __METHOD__));
+        return $this->getListeners($identifiers, $this->getEventName($event, __METHOD__));
     }
 
     /**

test/ListenerProvider/PrioritizedIdentifierListenerProviderTest.php

@@ -297,7 +297,7 @@ public function invalidEventNamesForFetchingListeners()
     {
         $types = $this->invalidEventNames();
         unset($types['non-traversable-object']);
-        yield from $types;
+        return $types;
     }
 
     /**