From fd6455218e304e9b484bebb0efcdb67bb52d051d Mon Sep 17 00:00:00 2001
From: Jordi Boggiano <j.boggiano@seld.be>
Date: Sat, 25 Jun 2016 15:49:52 +0100
Subject: [PATCH] Avoid warnings in case cache dir is explicitly directed to
 /dev/null, fixes #5468

---
 src/Composer/Cache.php | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Composer/Cache.php b/src/Composer/Cache.php
index a6044b630..4b1648841 100644
--- a/src/Composer/Cache.php
+++ b/src/Composer/Cache.php
@@ -44,6 +44,11 @@ class Cache
         $this->whitelist = $whitelist;
         $this->filesystem = $filesystem ?: new Filesystem();
 
+        if (preg_match('{(^|[\\\\/])(\$null|NUL|/dev/null)([\\\\/]|$)}', $cacheDir)) {
+            $this->enabled = false;
+            return;
+        }
+
         if (
             (!is_dir($this->root) && !Silencer::call('mkdir', $this->root, 0777, true))
             || !is_writable($this->root)