Omit Parent_Config section from returned configuration

- avoids problems with e.g. combined search, permissions handling.

module/VuFind/src/VuFind/Config/PluginFactory.php

@@ -113,6 +113,13 @@ class PluginFactory implements AbstractFactoryInterface
                 )
                 : [];
             foreach ($child as $section => $contents) {
+                // Omit Parent_Config from the returned configuration; it is only
+                // needed during loading, and its presence will cause problems in
+                // config files that iterate through all of the sections (e.g.
+                // combined.ini, permissions.ini).
+                if ($section === 'Parent_Config') {
+                    continue;
+                }
                 if (in_array($section, $overrideSections)
                     || !isset($config->$section)
                 ) {

module/VuFind/tests/unit-tests/src/VuFindTest/Config/PluginFactoryTest.php

@@ -177,6 +177,21 @@ class PluginFactoryTest extends \VuFindTest\Unit\TestCase
         $this->assertEquals('7', $config->Section3->g);
     }
 
+    /**
+     * Test that the plugin factory omits the Parent_Config section from the
+     * merged configuration.
+     *
+     * @void
+     */
+    public function testParentConfigOmission()
+    {
+        if (self::$writeFailed) {
+            $this->markTestSkipped('Could not write test configurations.');
+        }
+        $config = $this->getConfig('unit-test-child');
+        $this->assertFalse(isset($config->Parent_Config));
+    }
+
     /**
      * Test configuration is read-only.
      *