Fix extensions not being able to register other extensions

CHANGELOG.md

@@ -8,6 +8,10 @@ Updates should follow the [Keep a CHANGELOG](https://keepachangelog.com/) princi
 
  - Added the missing `addExtension()` method to the new `ConfigurableEnvironmentInterface`
 
+### Fixed
+
+ - Fixed extensions not being able to register other extensions
+
 ## [0.19.0] - 2019-04-10
 
 ### Added

src/Environment.php

@@ -32,6 +32,11 @@ final class Environment implements EnvironmentInterface, ConfigurableEnvironment
      */
     private $extensions = [];
 
+    /**
+     * @var ExtensionInterface[]
+     */
+    private $uninitializedExtensions = [];
+
     /**
      * @var bool
      */
@@ -308,6 +313,7 @@ public function addExtension(ExtensionInterface $extension): ConfigurableEnviron
         $this->assertUninitialized('Failed to add extension.');
 
         $this->extensions[] = $extension;
+        $this->uninitializedExtensions[] = $extension;
 
         return $this;
     }
@@ -320,8 +326,11 @@ private function initializeExtensions()
         }
 
         // Ask all extensions to register their components
-        foreach ($this->extensions as $extension) {
-            $extension->register($this);
+        while (!empty($this->uninitializedExtensions)) {
+            foreach ($this->uninitializedExtensions as $i => $extension) {
+                $extension->register($this);
+                unset($this->uninitializedExtensions[$i]);
+            }
         }
 
         $this->extensionsInitialized = true;