EventDispatcher uses only the return value of the last one listener, refs #9703

src/Composer/EventDispatcher/EventDispatcher.php

@@ -156,8 +156,9 @@ class EventDispatcher
 
         $this->pushEvent($event);
 
-        $return = 0;
+        $returnMax = 0;
         foreach ($listeners as $callable) {
+            $return = 0;
             $this->ensureBinDirIsInPath();
 
             if (!is_string($callable)) {
@@ -273,6 +274,8 @@ class EventDispatcher
                 }
             }
 
+            $returnMax = max($returnMax, $return);
+
             if ($event->isPropagationStopped()) {
                 break;
             }
@@ -280,7 +283,7 @@ class EventDispatcher
 
         $this->popEvent();
 
-        return $return;
+        return $returnMax;
     }
 
     protected function executeTty($exec)