Fix normalization of relative paths

src/Composer/Util/Filesystem.php

@@ -312,23 +312,30 @@ class Filesystem
         $parts = array();
         $path = strtr($path, '\\', '/');
         $prefix = '';
+        $absolute = false;
 
-        if (preg_match('{^((?:[0-9a-z]+://)?(?:[a-z]:)?/)}i', $path, $match)) {
+        if (preg_match('{^([0-9a-z]+:(?://(?:[a-z]:)?)?)}i', $path, $match)) {
             $prefix = $match[1];
             $path = substr($path, strlen($prefix));
         }
 
-        $appended = false;
+        if (substr($path, 0, 1) === '/') {
+            $absolute = true;
+            $path = substr($path, 1);
+        }
+
+        $up = false;
         foreach (explode('/', $path) as $chunk) {
-            if ('..' === $chunk && $appended) {
+            if ('..' === $chunk && ($absolute || $up)) {
                 array_pop($parts);
+                $up = !(empty($parts) || '..' === end($parts));
             } elseif ('.' !== $chunk && '' !== $chunk) {
-                $appended = true;
                 $parts[] = $chunk;
+                $up = '..' !== $chunk;
             }
         }
 
-        return $prefix.implode('/', $parts);
+        return $prefix.($absolute ? '/' : '').implode('/', $parts);
     }
 
     protected function directorySize($directory)

tests/Composer/Test/Util/FilesystemTest.php

@@ -160,6 +160,11 @@ class FilesystemTest extends TestCase
             array('phar://c:/Foo', 'phar://c:/Foo/Bar/..'),
             array('phar://c:/', 'phar://c:/Foo/Bar/../../../..'),
             array('/', '/Foo/Bar/../../../..'),
+            array('/', '/'),
+            array('c:/', 'c:\\'),
+            array('../src', 'Foo/Bar/../../../src'),
+            array('c:../b', 'c:.\\..\\a\\..\\b'),
+            array('phar://c:../Foo', 'phar://c:../Foo'),
         );
     }
 }