Merge branch '5.1' into 5.2

* 5.1:
  [Uid] fix checking for valid UUIDs
  [HttpKernel] Configure the ErrorHandler even when it is overriden
  Allow relative path to composer cache

Author: nicolas-grekas

bin/simple-phpunit.php

@@ -164,6 +164,18 @@
     ? ('#!/usr/bin/env php' === file_get_contents($COMPOSER, false, null, 0, 18) ? $PHP : '').' '.escapeshellarg($COMPOSER) // detect shell wrappers by looking at the shebang
     : 'composer';
 
+$prevCacheDir = getenv('COMPOSER_CACHE_DIR');
+if ($prevCacheDir) {
+    if (false === $absoluteCacheDir = realpath($prevCacheDir)) {
+        @mkdir($prevCacheDir, 0777, true);
+        $absoluteCacheDir = realpath($prevCacheDir);
+    }
+    if ($absoluteCacheDir) {
+        putenv("COMPOSER_CACHE_DIR=$absoluteCacheDir");
+    } else {
+        $prevCacheDir = false;
+    }
+}
 $SYMFONY_PHPUNIT_REMOVE = $getEnvVar('SYMFONY_PHPUNIT_REMOVE', 'phpspec/prophecy'.($PHPUNIT_VERSION < 6.0 ? ' symfony/yaml' : ''));
 $configurationHash = md5(implode(\PHP_EOL, [md5_file(__FILE__), $SYMFONY_PHPUNIT_REMOVE, (int) $PHPUNIT_REMOVE_RETURN_TYPEHINT]));
 $PHPUNIT_VERSION_DIR = sprintf('phpunit-%s-%d', $PHPUNIT_VERSION, $PHPUNIT_REMOVE_RETURN_TYPEHINT);
@@ -246,6 +258,9 @@
     // --no-suggest is not in the list to keep compat with composer 1.0, which is shipped with Ubuntu 16.04LTS
     $exit = proc_close(proc_open("$q$COMPOSER install --no-dev --prefer-dist --no-progress $q", [], $p, getcwd()));
     putenv('COMPOSER_ROOT_VERSION'.(false !== $prevRoot ? '='.$prevRoot : ''));
+    if ($prevCacheDir) {
+        putenv("COMPOSER_CACHE_DIR=$prevCacheDir");
+    }
     if ($exit) {
         exit($exit);
     }