Merge branch '5.1' into 5.2

* 5.1:
  Changed private static array-properties to const

Author: nicolas-grekas

Ldap.php

@@ -23,7 +23,7 @@ final class Ldap implements LdapInterface
 {
     private $adapter;
 
-    private static $adapterMap = [
+    private const ADAPTER_MAP = [
         'ext_ldap' => 'Symfony\Component\Ldap\Adapter\ExtLdap\Adapter',
     ];
 
@@ -74,11 +74,11 @@ public function escape(string $subject, string $ignore = '', int $flags = 0): st
      */
     public static function create(string $adapter, array $config = []): self
     {
-        if (!isset(self::$adapterMap[$adapter])) {
-            throw new DriverNotFoundException(sprintf('Adapter "%s" not found. You should use one of: "%s".', $adapter, implode('", "', self::$adapterMap)));
+        if (!isset(self::ADAPTER_MAP[$adapter])) {
+            throw new DriverNotFoundException(sprintf('Adapter "%s" not found. You should use one of: "%s".', $adapter, implode('", "', self::ADAPTER_MAP)));
         }
 
-        $class = self::$adapterMap[$adapter];
+        $class = self::ADAPTER_MAP[$adapter];
 
         return new self(new $class($config));
     }