Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Core/Installer/Exception/AlreadyInstalledException.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Exception\AlreadyInstalledException.
+ */
+
+namespace Drupal\Core\Installer\Exception;
+
+use Drupal\Core\StringTranslation\TranslationInterface;
+
+/**
+ * Exception thrown if Drupal is installed already.
+ */
+class AlreadyInstalledException extends InstallerException {
+
+  /**
+   * Constructs a new "already installed" exception.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The string translation manager.
+   */
+  public function __construct(TranslationInterface $string_translation) {
+    $this->stringTranslation = $string_translation;
+
+    $title = $this->t('Drupal already installed');
+    $message = $this->t('<ul>
+<li>To start over, you must empty your existing database and copy <em>default.settings.php</em> over <em>settings.php</em>.</li>
+<li>To upgrade an existing installation, proceed to the <a href="!update-url">update script</a>.</li>
+<li>View your <a href="!base-url">existing site</a>.</li>
+</ul>', array(
+      '!base-url' => $GLOBALS['base_url'],
+      '!update-url' => $GLOBALS['base_path'] . 'update.php',
+    ));
+    parent::__construct($message, $title);
+  }
+
+}

core/lib/Drupal/Core/Installer/Exception/InstallerException.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Exception\InstallerException.
+ */
+
+namespace Drupal\Core\Installer\Exception;
+
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
+/**
+ * Base class for exceptions thrown by installer.
+ */
+class InstallerException extends \RuntimeException {
+  use StringTranslationTrait;
+
+  /**
+   * The page title to output.
+   *
+   * @var string
+   */
+  protected $title;
+
+  /**
+   * Constructs a new installer exception.
+   *
+   * @param string $title
+   *   The page title.
+   * @param string $message
+   *   (optional) The exception message. Defaults to 'Error'.
+   * @param int $code
+   *   (optional) The exception code. Defaults to 0.
+   * @param \Exception $previous
+   *   (optional) A previous exception.
+   */
+  public function __construct($message, $title = 'Error', $code = 0, \Exception $previous = NULL) {
+    parent::__construct($message, $code, $previous);
+    $this->title = $title;
+  }
+
+  /**
+   * Returns the exception page title.
+   *
+   * @return string
+   */
+  public function getTitle() {
+    return $this->title;
+  }
+
+}

core/lib/Drupal/Core/Installer/Exception/NoProfilesException.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Exception\NoProfilesException.
+ */
+
+namespace Drupal\Core\Installer\Exception;
+
+use Drupal\Core\StringTranslation\TranslationInterface;
+
+/**
+ * Exception thrown if no installation profiles are available.
+ */
+class NoProfilesException extends InstallerException {
+
+  /**
+   * Constructs a new "no profiles available" exception.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The string translation manager.
+   */
+  public function __construct(TranslationInterface $string_translation) {
+    $this->stringTranslation = $string_translation;
+
+    $title = $this->t('No profiles available');
+    $message = $this->t('We were unable to find any installation profiles. Installation profiles tell us what modules to enable and what schema to install in the database. A profile is necessary to continue with the installation process.');
+    parent::__construct($message, $title);
+  }
+
+}

core/lib/Drupal/Core/Installer/Form/SelectLanguageForm.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Form\SelectLanguageForm.
+ */
+
+namespace Drupal\Core\Installer\Form;
+
+use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Utility\UserAgent;
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Language\LanguageManager;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Provides the language selection form.
+ */
+class SelectLanguageForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'install_select_language_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $install_state = NULL) {
+    if (count($install_state['translations']) > 1) {
+      $files = $install_state['translations'];
+    }
+    else {
+      $files = array();
+    }
+    $standard_languages = LanguageManager::getStandardLanguageList();
+    $select_options = array();
+    $browser_options = array();
+
+    $form['#title'] = $this->t('Choose language');
+
+    // Build a select list with language names in native language for the user
+    // to choose from. And build a list of available languages for the browser
+    // to select the language default from.
+    // Select lists based on all standard languages.
+    foreach ($standard_languages as $langcode => $language_names) {
+      $select_options[$langcode] = $language_names[1];
+      $browser_options[$langcode] = $langcode;
+    }
+    // Add languages based on language files in the translations directory.
+    if (count($files)) {
+      foreach ($files as $langcode => $uri) {
+        $select_options[$langcode] = isset($standard_languages[$langcode]) ? $standard_languages[$langcode][1] : $langcode;
+        $browser_options[$langcode] = $langcode;
+      }
+    }
+    asort($select_options);
+    $request = Request::createFromGlobals();
+    $browser_langcode = UserAgent::getBestMatchingLangcode($request->server->get('HTTP_ACCEPT_LANGUAGE'), $browser_options);
+    $form['langcode'] = array(
+      '#type' => 'select',
+      '#title' => $this->t('Choose language'),
+      '#title_display' => 'invisible',
+      '#options' => $select_options,
+      // Use the browser detected language as default or English if nothing found.
+      '#default_value' => !empty($browser_langcode) ? $browser_langcode : 'en',
+    );
+    $form['help'] = array(
+      '#type' => 'item',
+      '#markup' => SafeMarkup::format('<p>Translations will be downloaded from the <a href="http://localize.drupal.org">Drupal Translation website</a>.
+      If you do not want this, select <a href="!english">English</a>.</p>', array(
+          '!english' => install_full_redirect_url(array('parameters' => array('langcode' => 'en'))),
+        )),
+      '#states' => array(
+        'invisible' => array(
+          'select[name="langcode"]' => array('value' => 'en'),
+        ),
+      ),
+    );
+    $form['actions'] = array('#type' => 'actions');
+    $form['actions']['submit'] =  array(
+      '#type' => 'submit',
+      '#value' => $this->t('Save and continue'),
+      '#button_type' => 'primary',
+    );
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $build_info = $form_state->getBuildInfo();
+    $build_info['args'][0]['parameters']['langcode'] = $form_state->getValue('langcode');
+    $form_state->setBuildInfo($build_info);
+  }
+
+}

core/lib/Drupal/Core/Installer/Form/SelectProfileForm.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Form\SelectProfileForm.
+ */
+
+namespace Drupal\Core\Installer\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Provides the profile selection form.
+ */
+class SelectProfileForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'install_select_profile_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $install_state = NULL) {
+    $form['#title'] = $this->t('Select an installation profile');
+
+    $profiles = array();
+    $names = array();
+    foreach ($install_state['profiles'] as $profile) {
+      /** @var $profile \Drupal\Core\Extension\Extension */
+      $details = install_profile_info($profile->getName());
+      // Don't show hidden profiles. This is used by to hide the testing profile,
+      // which only exists to speed up test runs.
+      if ($details['hidden'] === TRUE && !drupal_valid_test_ua()) {
+        continue;
+      }
+      $profiles[$profile->getName()] = $details;
+
+      // Determine the name of the profile; default to file name if defined name
+      // is unspecified.
+      $name = isset($details['name']) ? $details['name'] : $profile->getName();
+      $names[$profile->getName()] = $name;
+    }
+
+    // Display radio buttons alphabetically by human-readable name, but always
+    // put the core profiles first (if they are present in the filesystem).
+    natcasesort($names);
+    if (isset($names['minimal'])) {
+      // If the expert ("Minimal") core profile is present, put it in front of
+      // any non-core profiles rather than including it with them alphabetically,
+      // since the other profiles might be intended to group together in a
+      // particular way.
+      $names = array('minimal' => $names['minimal']) + $names;
+    }
+    if (isset($names['standard'])) {
+      // If the default ("Standard") core profile is present, put it at the very
+      // top of the list. This profile will have its radio button pre-selected,
+      // so we want it to always appear at the top.
+      $names = array('standard' => $names['standard']) + $names;
+    }
+
+    // The profile name and description are extracted for translation from the
+    // .info file, so we can use $this->t() on them even though they are dynamic
+    // data at this point.
+    $form['profile'] = array(
+      '#type' => 'radios',
+      '#title' => $this->t('Select an installation profile'),
+      '#title_display' => 'invisible',
+      '#options' => array_map(array($this, 't'), $names),
+      '#default_value' => 'standard',
+    );
+    foreach (array_keys($names) as $profile_name) {
+      $form['profile'][$profile_name]['#description'] = isset($profiles[$profile_name]['description']) ? $this->t($profiles[$profile_name]['description']) : '';
+    }
+    $form['actions'] = array('#type' => 'actions');
+    $form['actions']['submit'] =  array(
+      '#type' => 'submit',
+      '#value' => $this->t('Save and continue'),
+      '#button_type' => 'primary',
+    );
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    global $install_state;
+    $install_state['parameters']['profile'] = $form_state->getValue('profile');
+  }
+
+}

core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Form\SiteConfigureForm.
+ */
+
+namespace Drupal\Core\Installer\Form;
+
+use Drupal\Core\Extension\ModuleInstallerInterface;
+use Drupal\Core\Form\ConfigFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Locale\CountryManagerInterface;
+use Drupal\Core\State\StateInterface;
+use Drupal\user\UserStorageInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides the site configuration form.
+ */
+class SiteConfigureForm extends ConfigFormBase {
+
+  /**
+   * The site path.
+   *
+   * @var string
+   */
+  protected $sitePath;
+
+  /**
+   * The user storage.
+   *
+   * @var \Drupal\user\UserStorageInterface
+   */
+  protected $userStorage;
+
+  /**
+   * The state service.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * The module installer.
+   *
+   * @var \Drupal\Core\Extension\ModuleInstallerInterface
+   */
+  protected $moduleInstaller;
+
+  /**
+   * The country manager.
+   *
+   * @var \Drupal\Core\Locale\CountryManagerInterface
+   */
+  protected $countryManager;
+
+  /**
+   * The app root.
+   *
+   * @var string
+   */
+  protected $root;
+
+  /**
+   * Constructs a new SiteConfigureForm.
+   *
+   * @param string $root
+   *   The app root.
+   * @param string $site_path
+   *   The site path.
+   * @param \Drupal\user\UserStorageInterface $user_storage
+   *   The user storage.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state service.
+   * @param \Drupal\Core\Extension\ModuleInstallerInterface $module_installer
+   *   The module installer.
+   * @param \Drupal\Core\Locale\CountryManagerInterface $country_manager
+   *   The country manager.
+   */
+  public function __construct($root, $site_path, UserStorageInterface $user_storage, StateInterface $state, ModuleInstallerInterface $module_installer, CountryManagerInterface $country_manager) {
+    $this->root = $root;
+    $this->sitePath = $site_path;
+    $this->userStorage = $user_storage;
+    $this->state = $state;
+    $this->moduleInstaller = $module_installer;
+    $this->countryManager = $country_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('app.root'),
+      $container->get('site.path'),
+      $container->get('entity.manager')->getStorage('user'),
+      $container->get('state'),
+      $container->get('module_installer'),
+      $container->get('country_manager')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'install_configure_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEditableConfigNames() {
+    return [
+      'system.date',
+      'system.site',
+      'update.settings',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['#title'] = $this->t('Configure site');
+
+    // Warn about settings.php permissions risk
+    $settings_dir = $this->sitePath;
+    $settings_file = $settings_dir . '/settings.php';
+    // Check that $_POST is empty so we only show this message when the form is
+    // first displayed, not on the next page after it is submitted. (We do not
+    // want to repeat it multiple times because it is a general warning that is
+    // not related to the rest of the installation process; it would also be
+    // especially out of place on the last page of the installer, where it would
+    // distract from the message that the Drupal installation has completed
+    // successfully.)
+    $post_params = $this->getRequest()->request->all();
+    if (empty($post_params) && (!drupal_verify_install_file($this->root . '/' . $settings_file, FILE_EXIST|FILE_READABLE|FILE_NOT_WRITABLE) || !drupal_verify_install_file($this->root . '/' . $settings_dir, FILE_NOT_WRITABLE, 'dir'))) {
+      drupal_set_message(t('All necessary changes to %dir and %file have been made, so you should remove write permissions to them now in order to avoid security risks. If you are unsure how to do so, consult the <a href="@handbook_url">online handbook</a>.', array('%dir' => $settings_dir, '%file' => $settings_file, '@handbook_url' => 'https://www.drupal.org/server-permissions')), 'warning');
+    }
+
+    $form['#attached']['library'][] = 'system/drupal.system';
+    // Add JavaScript time zone detection.
+    $form['#attached']['library'][] = 'core/drupal.timezone';
+    // We add these strings as settings because JavaScript translation does not
+    // work during installation.
+    $form['#attached']['drupalSettings']['copyFieldValue']['edit-site-mail'] = ['edit-account-mail'];
+
+    $form['site_information'] = array(
+      '#type' => 'fieldgroup',
+      '#title' => $this->t('Site information'),
+    );
+    $form['site_information']['site_name'] = array(
+      '#type' => 'textfield',
+      '#title' => $this->t('Site name'),
+      '#required' => TRUE,
+      '#weight' => -20,
+    );
+    $form['site_information']['site_mail'] = array(
+      '#type' => 'email',
+      '#title' => $this->t('Site email address'),
+      '#default_value' => ini_get('sendmail_from'),
+      '#description' => $this->t("Automated emails, such as registration information, will be sent from this address. Use an address ending in your site's domain to help prevent these emails from being flagged as spam."),
+      '#required' => TRUE,
+      '#weight' => -15,
+    );
+
+    $form['admin_account'] = array(
+      '#type' => 'fieldgroup',
+      '#title' => $this->t('Site maintenance account'),
+    );
+    $form['admin_account']['account']['name'] = array(
+      '#type' => 'textfield',
+      '#title' => $this->t('Username'),
+      '#maxlength' => USERNAME_MAX_LENGTH,
+      '#description' => $this->t('Spaces are allowed; punctuation is not allowed except for periods, hyphens, and underscores.'),
+      '#required' => TRUE,
+      '#attributes' => array('class' => array('username')),
+    );
+    $form['admin_account']['account']['pass'] = array(
+      '#type' => 'password_confirm',
+      '#required' => TRUE,
+      '#size' => 25,
+    );
+    $form['admin_account']['account']['#tree'] = TRUE;
+    $form['admin_account']['account']['mail'] = array(
+      '#type' => 'email',
+      '#title' => $this->t('Email address'),
+      '#required' => TRUE,
+    );
+
+    $form['regional_settings'] = array(
+      '#type' => 'fieldgroup',
+      '#title' => $this->t('Regional settings'),
+    );
+    $countries = $this->countryManager->getList();
+    $form['regional_settings']['site_default_country'] = array(
+      '#type' => 'select',
+      '#title' => $this->t('Default country'),
+      '#empty_value' => '',
+      '#default_value' => $this->config('system.date')->get('country.default'),
+      '#options' => $countries,
+      '#description' => $this->t('Select the default country for the site.'),
+      '#weight' => 0,
+    );
+    $form['regional_settings']['date_default_timezone'] = array(
+      '#type' => 'select',
+      '#title' => $this->t('Default time zone'),
+      // Use system timezone if set, but avoid throwing a warning in PHP >=5.4
+      '#default_value' => @date_default_timezone_get(),
+      '#options' => system_time_zones(),
+      '#description' => $this->t('By default, dates in this site will be displayed in the chosen time zone.'),
+      '#weight' => 5,
+      '#attributes' => array('class' => array('timezone-detect')),
+    );
+
+    $form['update_notifications'] = array(
+      '#type' => 'fieldgroup',
+      '#title' => $this->t('Update notifications'),
+    );
+    $form['update_notifications']['update_status_module'] = array(
+      '#type' => 'checkboxes',
+      '#title' => $this->t('Update notifications'),
+      '#options' => array(
+        1 => $this->t('Check for updates automatically'),
+        2 => $this->t('Receive email notifications'),
+      ),
+      '#default_value' => array(1, 2),
+      '#description' => $this->t('The system will notify you when updates and important security releases are available for installed components. Anonymous information about your site is sent to <a href="@drupal">Drupal.org</a>.', array('@drupal' => 'https://www.drupal.org')),
+      '#weight' => 15,
+    );
+    $form['update_notifications']['update_status_module'][2] = array(
+      '#states' => array(
+        'visible' => array(
+          'input[name="update_status_module[1]"]' => array('checked' => TRUE),
+        ),
+      ),
+    );
+
+    $form['actions'] = array('#type' => 'actions');
+    $form['actions']['submit'] = array(
+      '#type' => 'submit',
+      '#value' => $this->t('Save and continue'),
+      '#weight' => 15,
+      '#button_type' => 'primary',
+    );
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    if ($error = user_validate_name($form_state->getValue(array('account', 'name')))) {
+      $form_state->setErrorByName('account][name', $error);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->config('system.site')
+      ->set('name', (string) $form_state->getValue('site_name'))
+      ->set('mail', (string) $form_state->getValue('site_mail'))
+      ->save(TRUE);
+
+    $this->config('system.date')
+      ->set('timezone.default', (string) $form_state->getValue('date_default_timezone'))
+      ->set('country.default', (string) $form_state->getValue('site_default_country'))
+      ->save(TRUE);
+
+    $account_values = $form_state->getValue('account');
+
+    // Enable update.module if this option was selected.
+    $update_status_module = $form_state->getValue('update_status_module');
+    if ($update_status_module[1]) {
+      $this->moduleInstaller->install(array('file', 'update'), FALSE);
+
+      // Add the site maintenance account's email address to the list of
+      // addresses to be notified when updates are available, if selected.
+      if ($update_status_module[2]) {
+        // Reset the configuration factory so it is updated with the new module.
+        $this->resetConfigFactory();
+        $this->config('update.settings')->set('notification.emails', array($account_values['mail']))->save(TRUE);
+      }
+    }
+
+    // We precreated user 1 with placeholder values. Let's save the real values.
+    $account = $this->userStorage->load(1);
+    $account->init = $account->mail = $account_values['mail'];
+    $account->roles = $account->getRoles();
+    $account->activate();
+    $account->timezone = $form_state->getValue('date_default_timezone');
+    $account->pass = $account_values['pass'];
+    $account->name = $account_values['name'];
+    $account->save();
+
+    // Record when this install ran.
+    $this->state->set('install_time', $_SERVER['REQUEST_TIME']);
+  }
+
+}

core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php

@@ -0,0 +1,200 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\Form\SiteSettingsForm.
+ */
+
+namespace Drupal\Core\Installer\Form;
+
+use Drupal\Component\Utility\Crypt;
+use Drupal\Core\Database\Database;
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a form to configure and rewrite settings.php.
+ */
+class SiteSettingsForm extends FormBase {
+
+  /**
+   * The site path.
+   *
+   * @var string
+   */
+  protected $sitePath;
+
+  /**
+   * Constructs a new SiteSettingsForm.
+   *
+   * @param string $site_path
+   *   The site path.
+   */
+  public function __construct($site_path) {
+    $this->sitePath = $site_path;
+}
+
+  /**
+    * {@inheritdoc}
+    */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('site.path')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'install_settings_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $settings_file = './' . $this->sitePath . '/settings.php';
+
+    $form['#title'] = $this->t('Database configuration');
+
+    $drivers = drupal_get_database_types();
+    $drivers_keys = array_keys($drivers);
+
+    // Unless there is input for this form (for a non-interactive installation,
+    // input originates from the $settings array passed into install_drupal()),
+    // check whether database connection settings have been prepared in
+    // settings.php already.
+    // Note: The installer even executes this form if there is a valid database
+    // connection already, since the submit handler of this form is responsible
+    // for writing all $settings to settings.php (not limited to $databases).
+    $input = &$form_state->getUserInput();
+    if (!isset($input['driver']) && $database = Database::getConnectionInfo()) {
+      $input['driver'] = $database['default']['driver'];
+      $input[$database['default']['driver']] = $database['default'];
+    }
+
+    if (isset($input['driver'])) {
+      $default_driver = $input['driver'];
+      // In case of database connection info from settings.php, as well as for a
+      // programmed form submission (non-interactive installer), the table prefix
+      // information is usually normalized into an array already, but the form
+      // element only allows to configure one default prefix for all tables.
+      $prefix = &$input[$default_driver]['prefix'];
+      if (isset($prefix) && is_array($prefix)) {
+        $prefix = $prefix['default'];
+      }
+      $default_options = $input[$default_driver];
+    }
+    // If there is no database information yet, suggest the first available driver
+    // as default value, so that its settings form is made visible via #states
+    // when JavaScript is enabled (see below).
+    else {
+      $default_driver = current($drivers_keys);
+      $default_options = array();
+    }
+
+    $form['driver'] = array(
+      '#type' => 'radios',
+      '#title' => $this->t('Database type'),
+      '#required' => TRUE,
+      '#default_value' => $default_driver,
+    );
+    if (count($drivers) == 1) {
+      $form['driver']['#disabled'] = TRUE;
+    }
+
+    // Add driver specific configuration options.
+    foreach ($drivers as $key => $driver) {
+      $form['driver']['#options'][$key] = $driver->name();
+
+      $form['settings'][$key] = $driver->getFormOptions($default_options);
+      $form['settings'][$key]['#prefix'] = '<h2 class="js-hide">' . $this->t('@driver_name settings', array('@driver_name' => $driver->name())) . '</h2>';
+      $form['settings'][$key]['#type'] = 'container';
+      $form['settings'][$key]['#tree'] = TRUE;
+      $form['settings'][$key]['advanced_options']['#parents'] = array($key);
+      $form['settings'][$key]['#states'] = array(
+        'visible' => array(
+          ':input[name=driver]' => array('value' => $key),
+        )
+      );
+    }
+
+    $form['actions'] = array('#type' => 'actions');
+    $form['actions']['save'] = array(
+      '#type' => 'submit',
+      '#value' => $this->t('Save and continue'),
+      '#button_type' => 'primary',
+      '#limit_validation_errors' => array(
+        array('driver'),
+        array($default_driver),
+      ),
+      '#submit' => array('::submitForm'),
+    );
+
+    $form['errors'] = array();
+    $form['settings_file'] = array('#type' => 'value', '#value' => $settings_file);
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    $driver = $form_state->getValue('driver');
+    $database = $form_state->getValue($driver);
+    $drivers = drupal_get_database_types();
+    $reflection = new \ReflectionClass($drivers[$driver]);
+    $install_namespace = $reflection->getNamespaceName();
+    // Cut the trailing \Install from namespace.
+    $database['namespace'] = substr($install_namespace, 0, strrpos($install_namespace, '\\'));
+    $database['driver'] = $driver;
+
+    $form_state->set('database', $database);
+    $errors = install_database_errors($database, $form_state->getValue('settings_file'));
+    foreach ($errors as $name => $message) {
+      $form_state->setErrorByName($name, $message);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    global $install_state;
+
+    // Update global settings array and save.
+    $settings = array();
+    $database = $form_state->get('database');
+    $settings['databases']['default']['default'] = (object) array(
+      'value'    => $database,
+      'required' => TRUE,
+    );
+    $settings['settings']['hash_salt'] = (object) array(
+      'value'    => Crypt::randomBytesBase64(55),
+      'required' => TRUE,
+    );
+    // Remember the profile which was used.
+    $settings['settings']['install_profile'] = (object) array(
+      'value' => $install_state['parameters']['profile'],
+      'required' => TRUE,
+    );
+
+    drupal_rewrite_settings($settings);
+
+    // Add the config directories to settings.php.
+    drupal_install_config_directories();
+
+    // Indicate that the settings file has been verified, and check the database
+    // for the last completed task, now that we have a valid connection. This
+    // last step is important since we want to trigger an error if the new
+    // database already has Drupal installed.
+    $install_state['settings_verified'] = TRUE;
+    $install_state['config_verified'] = TRUE;
+    $install_state['database_verified'] = TRUE;
+    $install_state['completed_task'] = install_verify_completed_task();
+  }
+
+}

core/lib/Drupal/Core/Installer/InstallerKernel.php

@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\InstallerKernel.
+ */
+
+namespace Drupal\Core\Installer;
+
+use Drupal\Core\DrupalKernel;
+
+/**
+ * Extend DrupalKernel to handle force some kernel behaviors.
+ */
+class InstallerKernel extends DrupalKernel {
+
+  /**
+   * {@inheritdoc}
+   *
+   * @param bool $rebuild
+   *   Force a container rebuild. Unlike the parent method, this defaults to
+   *   TRUE.
+   */
+  protected function initializeContainer($rebuild = TRUE) {
+    $container = parent::initializeContainer($rebuild);
+    return $container;
+  }
+
+  /**
+   * Reset the bootstrap config storage.
+   *
+   * Use this from a database driver runTasks() if the method overrides the
+   * bootstrap config storage. Normally the bootstrap config storage is not
+   * re-instantiated during a single install request. Most drivers will not
+   * need this method.
+   *
+   * @see \Drupal\Core\Database\Install\Tasks::runTasks().
+   */
+  public function resetConfigStorage() {
+    $this->configStorage = NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function addServiceFiles($service_yamls) {
+    // In the beginning there is no settings.php and no service YAMLs.
+    return parent::addServiceFiles($service_yamls ?: []);
+  }
+}

core/lib/Drupal/Core/Installer/InstallerRouteBuilder.php

@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\InstallerRouteBuilder.
+ */
+
+namespace Drupal\Core\Installer;
+
+use Drupal\Core\Routing\RouteBuilder;
+
+/**
+ * Manages the router in the installer.
+ */
+class InstallerRouteBuilder extends RouteBuilder {
+
+  /**
+   * {@inheritdoc}
+   *
+   * Overridden to return no routes.
+   *
+   * @todo Convert installer steps into routes; add an installer.routing.yml.
+   */
+  protected function getRouteDefinitions() {
+    return array();
+  }
+
+}

core/lib/Drupal/Core/Installer/InstallerServiceProvider.php

@@ -0,0 +1,84 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Installer\InstallerServiceProvider.
+ */
+
+namespace Drupal\Core\Installer;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\DependencyInjection\ServiceProviderInterface;
+use Drupal\Core\DependencyInjection\ServiceModifierInterface;
+use Symfony\Component\DependencyInjection\Reference;
+
+/**
+ * Service provider for the early installer environment.
+ *
+ * This class is manually added by install_begin_request() via
+ * $conf['container_service_providers'] and required to prevent various services
+ * from trying to retrieve data from storages that do not exist yet.
+ */
+class InstallerServiceProvider implements ServiceProviderInterface, ServiceModifierInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container) {
+    // Inject the special configuration storage for the installer.
+    // This special implementation MUST NOT be used anywhere else than the early
+    // installer environment.
+    $container->register('config.storage', 'Drupal\Core\Config\InstallStorage');
+
+    // Replace services with in-memory implementations.
+    $definition = $container->getDefinition('cache_factory');
+    $definition->setClass('Drupal\Core\Cache\MemoryBackendFactory');
+    $definition->setArguments(array());
+    $definition->setMethodCalls(array());
+    $container
+      ->register('keyvalue', 'Drupal\Core\KeyValueStore\KeyValueMemoryFactory');
+    $container
+      ->register('keyvalue.expirable', 'Drupal\Core\KeyValueStore\KeyValueNullExpirableFactory');
+
+    // Replace services with no-op implementations.
+    $container
+      ->register('lock', 'Drupal\Core\Lock\NullLockBackend');
+    $container
+      ->register('url_generator', 'Drupal\Core\Routing\NullGenerator')
+      ->addArgument(new Reference('request_stack'));
+    $container
+      ->register('router.dumper', 'Drupal\Core\Routing\NullMatcherDumper');
+
+    // Remove the cache tags invalidator tag from the cache tags storage, so
+    // that we don't call it when cache tags are invalidated very early in the
+    // installer.
+    $container->getDefinition('cache_tags.invalidator.checksum')
+      ->clearTag('cache_tags_invalidator');
+
+    // Replace the route builder with an empty implementation.
+    // @todo Convert installer steps into routes; add an installer.routing.yml.
+    $definition = $container->getDefinition('router.builder');
+    $definition->setClass('Drupal\Core\Installer\InstallerRouteBuilder');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function alter(ContainerBuilder $container) {
+    // Disable Twig cache (php storage does not exist yet).
+    $twig_config = $container->getParameter('twig.config');
+    $twig_config['cache'] = FALSE;
+    $container->setParameter('twig.config', $twig_config);
+
+    // No service may persist when the early installer kernel is rebooted into
+    // the production environment.
+    // @todo The DrupalKernel reboot performed by drupal_install_system() is
+    //   actually not a "regular" reboot (like ModuleHandler::install()), so
+    //   services are not actually persisted.
+    foreach ($container->findTaggedServiceIds('persist') as $id => $tags) {
+      $definition = $container->getDefinition($id);
+      $definition->clearTag('persist');
+    }
+  }
+
+}