Issue #2342925 by tim.plunkett: Simplify url() in order for the installer to function without it.

core/includes/common.inc

@@ -642,21 +642,7 @@ function _format_date_callback(array $matches = NULL, $new_langcode = NULL) {
  * @see \Drupal\Core\Routing\UrlGeneratorInterface::generateFromPath().
  */
 function url($path = NULL, array $options = array()) {
-  $generator = \Drupal::urlGenerator();
-  try {
-    $url = $generator->generateFromPath($path, $options);
-  }
-  catch (GeneratorNotInitializedException $e) {
-    // Fallback to using globals.
-    // @todo Remove this once there is no code that calls url() when there is
-    //   no request.
-    global $base_url, $base_path, $script_path;
-    $generator->setBasePath($base_path);
-    $generator->setBaseUrl($base_url . '/');
-    $generator->setScriptPath($script_path);
-    $url = $generator->generateFromPath($path, $options);
-  }
-  return $url;
+  return \Drupal::urlGenerator()->generateFromPath($path, $options);
 }
 
 /**

core/includes/install.core.inc

@@ -886,6 +886,9 @@ function install_display_output($output, $install_state) {
   // reached in case of an early installer error.
   drupal_maintenance_theme();
 
+  // Ensure the URL generator is initialized.
+  \Drupal::urlGenerator()->updateFromRequest();
+
   drupal_page_header();
 
   // Prevent install.php from being indexed when installed in a sub folder.

core/lib/Drupal/Core/Routing/NullGenerator.php

@@ -22,6 +22,16 @@ class NullGenerator extends UrlGenerator {
   public function __construct() {
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function updateFromRequest() {
+    global $base_url, $base_path, $script_path;
+    $this->basePath = $base_path;
+    $this->baseUrl = $base_url . '/';
+    $this->scriptPath = $script_path;
+  }
+
   /**
    * {@inheritdoc}
    *