Autoloader infinite recursion fix (#1031)

* Autoloader infinite recursion fix

Fixes simplesamlphp/simplesamlphp#1030

* Added test to ensure old autoloader behaviour is preserved

Also fixed undefined variable notice

lib/_autoload_modules.php

@@ -22,9 +22,9 @@ function temporaryLoader($class)
     // handle the upgrade to the latest version of XMLSecLibs using namespaces
     if (strstr($class, 'XMLSec') && !strstr($class, '\\RobRichards\\XMLSecLibs\\')) {
         $new = '\\RobRichards\\XMLSecLibs\\'.$class;
-        if (class_exists($new, false)) {
+        if (class_exists($new, true)) {
             class_alias($new, $class);
-            SimpleSAML\Logger::warning("The class or interface '$original' is now using namespaces, please use '$new'.");
+            SimpleSAML\Logger::warning("The class or interface '$class' is now using namespaces, please use '$new'.");
             return;
         }
     }

tests/lib/AutoloadModulesTest.php

+<?php
+
+namespace SimpleSAML\Test;
+
+use PHPUnit\Framework\TestCase;
+
+class AutoloadModulesTest extends TestCase
+{
+    /**
+     * @test
+     * @runInSeparateProcess
+     */
+    public function autoloaderDoesNotRecurseInfinitely()
+    {
+        $this->assertFalse(class_exists('NonExisting\\ClassThatHasNothing\\ToDoWithXMLSec\\Library', true));
+    }
+
+    /**
+     * @test
+     * @runInSeparateProcess
+     */
+    public function autoloaderSubstitutesNamespacedXmlSecClassesWhereNonNamespacedClassWasUsed()
+    {
+        $this->assertTrue(class_exists('XMLSecEnc', true));
+    }
+}