From fc0da27d847f2b628d0cc10b0d9a581264a79126 Mon Sep 17 00:00:00 2001
From: Jordi Boggiano <j.boggiano@seld.be>
Date: Tue, 10 Nov 2015 13:12:47 +0000
Subject: [PATCH] Add more debug output when writing to cache

---
 src/Composer/Cache.php | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/Composer/Cache.php b/src/Composer/Cache.php
index 9f9c55ba6..3ba11da1c 100644
--- a/src/Composer/Cache.php
+++ b/src/Composer/Cache.php
@@ -124,8 +124,10 @@ class Cache
             $file = preg_replace('{[^'.$this->whitelist.']}i', '-', $file);
             $this->filesystem->ensureDirectoryExists(dirname($this->root . $file));
 
-            if ($this->io->isDebug()) {
-                $this->io->writeError('Writing '.$this->root . $file.' into cache');
+            if (!file_exists($source)) {
+                $this->io->writeError('<error>'.$source.' does not exist, can not write into cache</error>');
+            } elseif ($this->io->isDebug()) {
+                $this->io->writeError('Writing '.$this->root . $file.' into cache from '.$source);
             }
 
             return copy($source, $this->root . $file);