composer/Plugin/Scaffold/CommandProvider.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Plugin\Capability\CommandProvider as CommandProviderCapability;
+
+/**
+ * List of all commands provided by this package.
+ *
+ * @internal
+ */
+class CommandProvider implements CommandProviderCapability {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCommands() {
+    return [new ComposerScaffoldCommand()];
+  }
+
+}

composer/Plugin/Scaffold/ComposerScaffoldCommand.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Command\BaseCommand;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * The "drupal:scaffold" command class.
+ *
+ * Manually run the scaffold operation that normally happens after
+ * 'composer install'.
+ *
+ * @internal
+ */
+class ComposerScaffoldCommand extends BaseCommand {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function configure() {
+    $this
+      ->setName('drupal:scaffold')
+      ->setAliases(['scaffold'])
+      ->setDescription('Update the Drupal scaffold files.')
+      ->setHelp(
+        <<<EOT
+The <info>drupal:scaffold</info> command places the scaffold files in their
+respective locations according to the layout stipulated in the composer.json
+file.
+
+<info>php composer.phar drupal:scaffold</info>
+
+It is usually not necessary to call <info>drupal:scaffold</info> manually,
+because it is called automatically as needed, e.g. after an <info>install</info>
+or <info>update</info> command. Note, though, that only packages explicitly
+allowed to scaffold in the top-level composer.json will be processed by this
+command.
+
+For more information, see https://www.drupal.org/docs/develop/using-composer/using-drupals-composer-scaffold.
+EOT
+            );
+
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function execute(InputInterface $input, OutputInterface $output): int {
+    $handler = new Handler($this->requireComposer(), $this->getIO());
+    $handler->scaffold();
+    return 0;
+  }
+
+}

composer/Plugin/Scaffold/GenerateAutoloadReferenceFile.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\IO\IOInterface;
+use Composer\Util\Filesystem;
+use Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult;
+
+/**
+ * Generates an 'autoload.php' that includes the autoloader created by Composer.
+ *
+ * @internal
+ */
+final class GenerateAutoloadReferenceFile {
+
+  /**
+   * This class provides only static methods.
+   */
+  private function __construct() {
+  }
+
+  /**
+   * Generates the autoload file at the specified location.
+   *
+   * This only writes a bit of PHP that includes the autoload file that
+   * Composer generated. Drupal does this so that it can guarantee that there
+   * will always be an `autoload.php` file in a well-known location.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   IOInterface to write to.
+   * @param string $package_name
+   *   The name of the package defining the autoload file (the root package).
+   * @param string $web_root
+   *   The path to the web root.
+   * @param string $vendor
+   *   The path to the vendor directory.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult
+   *   The result of the autoload file generation.
+   */
+  public static function generateAutoload(IOInterface $io, $package_name, $web_root, $vendor) {
+    $autoload_path = static::autoloadPath($package_name, $web_root);
+    // Calculate the relative path from the webroot (location of the project
+    // autoload.php) to the vendor directory.
+    $fs = new Filesystem();
+    $relative_autoload_path = $fs->findShortestPath($autoload_path->fullPath(), "$vendor/autoload.php");
+    file_put_contents($autoload_path->fullPath(), static::autoLoadContents($relative_autoload_path));
+    return new ScaffoldResult($autoload_path, TRUE);
+  }
+
+  /**
+   * Determines whether or not the autoload file has been committed.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   IOInterface to write to.
+   * @param string $package_name
+   *   The name of the package defining the autoload file (the root package).
+   * @param string $web_root
+   *   The path to the web root.
+   *
+   * @return bool
+   *   True if autoload.php file exists and has been committed to the repository
+   */
+  public static function autoloadFileCommitted(IOInterface $io, $package_name, $web_root) {
+    $autoload_path = static::autoloadPath($package_name, $web_root);
+    $autoload_file = $autoload_path->fullPath();
+    $location = dirname($autoload_file);
+    if (!file_exists($autoload_file)) {
+      return FALSE;
+    }
+    return Git::checkTracked($io, $autoload_file, $location);
+  }
+
+  /**
+   * Generates a scaffold file path object for the autoload file.
+   *
+   * @param string $package_name
+   *   The name of the package defining the autoload file (the root package).
+   * @param string $web_root
+   *   The path to the web root.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   *   Object wrapping the relative and absolute path to the destination file.
+   */
+  protected static function autoloadPath($package_name, $web_root) {
+    $rel_path = 'autoload.php';
+    $dest_rel_path = '[web-root]/' . $rel_path;
+    $dest_full_path = $web_root . '/' . $rel_path;
+    return new ScaffoldFilePath('autoload', $package_name, $dest_rel_path, $dest_full_path);
+  }
+
+  /**
+   * Builds the contents of the autoload file.
+   *
+   * @param string $relative_autoload_path
+   *   The relative path to the autoloader in vendor.
+   *
+   * @return string
+   *   Return the contents for the autoload.php.
+   */
+  protected static function autoLoadContents($relative_autoload_path) {
+    $relative_autoload_path = preg_replace('#^\./#', '', $relative_autoload_path);
+    return <<<EOF
+<?php
+
+/**
+ * @file
+ * Includes the autoloader created by Composer.
+ *
+ * This file was generated by drupal-scaffold.
+ *
+ * @see composer.json
+ * @see index.php
+ * @see core/install.php
+ * @see core/rebuild.php
+ */
+
+return require __DIR__ . '/{$relative_autoload_path}';
+
+EOF;
+  }
+
+}

composer/Plugin/Scaffold/Git.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+// cspell:ignore unmatch
+
+use Composer\IO\IOInterface;
+use Composer\Util\ProcessExecutor;
+
+/**
+ * Provide some Git utility operations.
+ *
+ * @internal
+ */
+class Git {
+
+  /**
+   * This class provides only static methods.
+   */
+  private function __construct() {
+  }
+
+  /**
+   * Determines whether the specified scaffold file is already ignored.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO interface.
+   * @param string $path
+   *   Path to scaffold file to check.
+   * @param string $dir
+   *   Base directory for git process.
+   *
+   * @return bool
+   *   Whether the specified file is already ignored or not (TRUE if ignored).
+   */
+  public static function checkIgnore(IOInterface $io, $path, $dir = NULL) {
+    $process = new ProcessExecutor($io);
+    $output = '';
+    $exitCode = $process->execute('git check-ignore ' . $process->escape($path), $output, $dir);
+    return $exitCode == 0;
+  }
+
+  /**
+   * Determines whether the specified scaffold file is tracked by git.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO interface.
+   * @param string $path
+   *   Path to scaffold file to check.
+   * @param string $dir
+   *   Base directory for git process.
+   *
+   * @return bool
+   *   Whether the specified file is already tracked or not (TRUE if tracked).
+   */
+  public static function checkTracked(IOInterface $io, $path, $dir = NULL) {
+    $process = new ProcessExecutor($io);
+    $output = '';
+    $exitCode = $process->execute('git ls-files --error-unmatch ' . $process->escape($path), $output, $dir);
+    return $exitCode == 0;
+  }
+
+  /**
+   * Checks to see if the project root dir is in a git repository.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO interface.
+   * @param string $dir
+   *   Base directory for git process.
+   *
+   * @return bool
+   *   True if this is a repository.
+   */
+  public static function isRepository(IOInterface $io, $dir = NULL) {
+    $process = new ProcessExecutor($io);
+    $output = '';
+    $exitCode = $process->execute('git rev-parse --show-toplevel', $output, $dir);
+    return $exitCode == 0;
+  }
+
+}

composer/Plugin/Scaffold/Handler.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Composer;
+use Composer\Installer\PackageEvent;
+use Composer\IO\IOInterface;
+use Composer\Package\PackageInterface;
+use Composer\Util\Filesystem;
+use Drupal\Composer\Plugin\Scaffold\Operations\OperationData;
+use Drupal\Composer\Plugin\Scaffold\Operations\OperationFactory;
+use Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldFileCollection;
+
+/**
+ * Core class of the plugin.
+ *
+ * Contains the primary logic which determines the files to be fetched and
+ * processed.
+ *
+ * @internal
+ */
+class Handler {
+
+  /**
+   * Composer hook called before scaffolding begins.
+   */
+  const PRE_DRUPAL_SCAFFOLD_CMD = 'pre-drupal-scaffold-cmd';
+
+  /**
+   * Composer hook called after scaffolding completes.
+   */
+  const POST_DRUPAL_SCAFFOLD_CMD = 'post-drupal-scaffold-cmd';
+
+  /**
+   * The Composer service.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * Composer's I/O service.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * The scaffold options in the top-level composer.json's 'extra' section.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ManageOptions
+   */
+  protected $manageOptions;
+
+  /**
+   * The manager that keeps track of which packages are allowed to scaffold.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\AllowedPackages
+   */
+  protected $manageAllowedPackages;
+
+  /**
+   * The list of listeners that are notified after a package event.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\PostPackageEventListenerInterface[]
+   */
+  protected $postPackageListeners = [];
+
+  /**
+   * Handler constructor.
+   *
+   * @param \Composer\Composer $composer
+   *   The Composer service.
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer I/O service.
+   */
+  public function __construct(Composer $composer, IOInterface $io) {
+    $this->composer = $composer;
+    $this->io = $io;
+    $this->manageOptions = new ManageOptions($composer);
+    $this->manageAllowedPackages = new AllowedPackages($composer, $io, $this->manageOptions);
+  }
+
+  /**
+   * Registers post-package events if the 'require' command was called.
+   */
+  public function requireWasCalled() {
+    // In order to differentiate between post-package events called after
+    // 'composer require' vs. the same events called at other times, we will
+    // only install our handler when a 'require' event is detected.
+    $this->postPackageListeners[] = $this->manageAllowedPackages;
+  }
+
+  /**
+   * Posts package command event.
+   *
+   * We want to detect packages 'require'd that have scaffold files, but are not
+   * yet allowed in the top-level composer.json file.
+   *
+   * @param \Composer\Installer\PackageEvent $event
+   *   Composer package event sent on install/update/remove.
+   */
+  public function onPostPackageEvent(PackageEvent $event) {
+    foreach ($this->postPackageListeners as $listener) {
+      $listener->event($event);
+    }
+  }
+
+  /**
+   * Creates scaffold operation objects for all items in the file mappings.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package that relative paths will be relative from.
+   * @param array $package_file_mappings
+   *   The package file mappings array keyed by destination path and the values
+   *   are operation metadata arrays.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface[]
+   *   A list of scaffolding operation objects
+   */
+  protected function createScaffoldOperations(PackageInterface $package, array $package_file_mappings) {
+    $scaffold_op_factory = new OperationFactory($this->composer);
+    $scaffold_ops = [];
+    foreach ($package_file_mappings as $dest_rel_path => $data) {
+      $operation_data = new OperationData($dest_rel_path, $data);
+      $scaffold_ops[$dest_rel_path] = $scaffold_op_factory->create($package, $operation_data);
+    }
+    return $scaffold_ops;
+  }
+
+  /**
+   * Copies all scaffold files from source to destination.
+   */
+  public function scaffold() {
+    // Recursively get the list of allowed packages. Only allowed packages
+    // may declare scaffold files. Note that the top-level composer.json file
+    // is implicitly allowed.
+    $allowed_packages = $this->manageAllowedPackages->getAllowedPackages();
+    if (empty($allowed_packages)) {
+      $this->io->write("Nothing scaffolded because no packages are allowed in the top-level composer.json file.");
+      return;
+    }
+
+    // Call any pre-scaffold scripts that may be defined.
+    $dispatcher = $this->composer->getEventDispatcher();
+    $dispatcher->dispatchScript(self::PRE_DRUPAL_SCAFFOLD_CMD);
+
+    // Fetch the list of file mappings from each allowed package and normalize
+    // them.
+    $file_mappings = $this->getFileMappingsFromPackages($allowed_packages);
+
+    $location_replacements = $this->manageOptions->getLocationReplacements();
+    $scaffold_options = $this->manageOptions->getOptions();
+
+    // Create a collection of scaffolded files to process. This determines which
+    // take priority and which are combined.
+    $scaffold_files = new ScaffoldFileCollection($file_mappings, $location_replacements);
+
+    // Get the scaffold files whose contents on disk match what we are about to
+    // write. We can remove these from consideration, as rewriting would be a
+    // no-op.
+    $unchanged = $scaffold_files->checkUnchanged();
+    $scaffold_files->filterFiles($unchanged);
+
+    // Process the list of scaffolded files.
+    $scaffold_results = $scaffold_files->processScaffoldFiles($this->io, $scaffold_options);
+
+    // Generate an autoload file in the document root that includes the
+    // autoload.php file in the vendor directory, wherever that is. Drupal
+    // requires this in order to easily locate relocated vendor dirs.
+    $web_root = $this->manageOptions->getOptions()->getLocation('web-root');
+    if (!GenerateAutoloadReferenceFile::autoloadFileCommitted($this->io, $this->rootPackageName(), $web_root)) {
+      $scaffold_results[] = GenerateAutoloadReferenceFile::generateAutoload($this->io, $this->rootPackageName(), $web_root, $this->getVendorPath());
+    }
+
+    // Add the managed scaffold files to .gitignore if applicable.
+    $gitIgnoreManager = new ManageGitIgnore($this->io, getcwd());
+    $gitIgnoreManager->manageIgnored($scaffold_results, $scaffold_options);
+
+    // Call post-scaffold scripts.
+    $dispatcher->dispatchScript(self::POST_DRUPAL_SCAFFOLD_CMD);
+  }
+
+  /**
+   * Gets the path to the 'vendor' directory.
+   *
+   * @return string
+   *   The file path of the vendor directory.
+   */
+  protected function getVendorPath() {
+    $vendor_dir = $this->composer->getConfig()->get('vendor-dir');
+    $filesystem = new Filesystem();
+    return $filesystem->normalizePath(realpath($vendor_dir));
+  }
+
+  /**
+   * Gets a consolidated list of file mappings from all allowed packages.
+   *
+   * @param \Composer\Package\PackageInterface[] $allowed_packages
+   *   A multidimensional array of file mappings, as returned by
+   *   self::getAllowedPackages().
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface[][]
+   *   An array of destination paths => scaffold operation objects.
+   */
+  protected function getFileMappingsFromPackages(array $allowed_packages) {
+    $file_mappings = [];
+    foreach ($allowed_packages as $package_name => $package) {
+      $file_mappings[$package_name] = $this->getPackageFileMappings($package);
+    }
+    return $file_mappings;
+  }
+
+  /**
+   * Gets the array of file mappings provided by a given package.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The Composer package from which to get the file mappings.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface[]
+   *   An array of destination paths => scaffold operation objects.
+   */
+  protected function getPackageFileMappings(PackageInterface $package) {
+    $options = $this->manageOptions->packageOptions($package);
+    if ($options->hasFileMapping()) {
+      return $this->createScaffoldOperations($package, $options->fileMapping());
+    }
+    // Warn the user if they allow a package that does not have any scaffold
+    // files. We will ignore drupal/core, though, as it is implicitly allowed,
+    // but might not have scaffold files (version 8.7.x and earlier).
+    if (!$options->hasAllowedPackages() && ($package->getName() != 'drupal/core')) {
+      $this->io->writeError("The allowed package {$package->getName()} does not provide a file mapping for Composer Scaffold.");
+    }
+    return [];
+  }
+
+  /**
+   * Gets the root package name.
+   *
+   * @return string
+   *   The package name of the root project
+   */
+  protected function rootPackageName() {
+    $root_package = $this->composer->getPackage();
+    return $root_package->getName();
+  }
+
+}

composer/Plugin/Scaffold/Interpolator.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+/**
+ * Injects config values from an associative array into a string.
+ *
+ * @internal
+ */
+class Interpolator {
+
+  /**
+   * The character sequence that identifies the start of a token.
+   *
+   * @var string
+   */
+  protected $startToken;
+
+  /**
+   * The character sequence that identifies the end of a token.
+   *
+   * @var string
+   */
+  protected $endToken;
+
+  /**
+   * The associative array of replacements.
+   *
+   * @var array
+   */
+  protected $data = [];
+
+  /**
+   * Interpolator constructor.
+   *
+   * @param string $start_token
+   *   The start marker for a token, e.g. '['.
+   * @param string $end_token
+   *   The end marker for a token, e.g. ']'.
+   */
+  public function __construct($start_token = '\\[', $end_token = '\\]') {
+    $this->startToken = $start_token;
+    $this->endToken = $end_token;
+  }
+
+  /**
+   * Sets the data set to use when interpolating.
+   *
+   * @param array $data
+   *   The key:value pairs to use when interpolating.
+   *
+   * @return $this
+   */
+  public function setData(array $data) {
+    $this->data = $data;
+    return $this;
+  }
+
+  /**
+   * Adds to the data set to use when interpolating.
+   *
+   * @param array $data
+   *   The key:value pairs to use when interpolating.
+   *
+   * @return $this
+   */
+  public function addData(array $data) {
+    $this->data = array_merge($this->data, $data);
+    return $this;
+  }
+
+  /**
+   * Replaces tokens in a string with values from an associative array.
+   *
+   * Tokens are surrounded by delimiters, e.g. square brackets "[key]". The
+   * characters that surround the key may be defined when the Interpolator is
+   * constructed.
+   *
+   * Example:
+   * If the message is 'Hello, [user.name]', then the value of the user.name
+   * item is fetched from the array, and the token [user.name] is replaced with
+   * the result.
+   *
+   * @param string $message
+   *   Message containing tokens to be replaced.
+   * @param array $extra
+   *   Data to use for interpolation in addition to whatever was provided to
+   *   self::setData().
+   * @param string|bool $default
+   *   (optional) The value to substitute for tokens that are not found in the
+   *   data. If FALSE, then missing tokens are not replaced. Defaults to an
+   *   empty string.
+   *
+   * @return string
+   *   The message after replacements have been made.
+   */
+  public function interpolate($message, array $extra = [], $default = '') {
+    $data = $extra + $this->data;
+    $replacements = $this->replacements($message, $data, $default);
+    return strtr($message, $replacements);
+  }
+
+  /**
+   * Finds the tokens that exist in a message and builds a replacement array.
+   *
+   * All of the replacements in the data array are looked up given the token
+   * keys from the provided message. Keys that do not exist in the configuration
+   * are replaced with the default value.
+   *
+   * @param string $message
+   *   String with tokens.
+   * @param array $data
+   *   Data to use for interpolation.
+   * @param string $default
+   *   (optional) The value to substitute for tokens that are not found in the
+   *   data. If FALSE, then missing tokens are not replaced. Defaults to an
+   *   empty string.
+   *
+   * @return string[]
+   *   An array of replacements to make. Keyed by tokens and the replacements
+   *   are the values.
+   */
+  protected function replacements($message, array $data, $default = '') {
+    $tokens = $this->findTokens($message);
+    $replacements = [];
+    foreach ($tokens as $sourceText => $key) {
+      $replacement_text = array_key_exists($key, $data) ? $data[$key] : $default;
+      if ($replacement_text !== FALSE) {
+        $replacements[$sourceText] = $replacement_text;
+      }
+    }
+    return $replacements;
+  }
+
+  /**
+   * Finds all of the tokens in the provided message.
+   *
+   * @param string $message
+   *   String with tokens.
+   *
+   * @return string[]
+   *   map of token to key, e.g. {{key}} => key
+   */
+  protected function findTokens($message) {
+    $reg_ex = '#' . $this->startToken . '([a-zA-Z0-9._-]+)' . $this->endToken . '#';
+    if (!preg_match_all($reg_ex, $message, $matches, PREG_SET_ORDER)) {
+      return [];
+    }
+    $tokens = [];
+    foreach ($matches as $matchSet) {
+      [$sourceText, $key] = $matchSet;
+      $tokens[$sourceText] = $key;
+    }
+    return $tokens;
+  }
+
+}

composer/Plugin/Scaffold/LICENSE.txt

+        GNU GENERAL PUBLIC LICENSE
+           Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+          Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
+program will individually obtain patent licenses, in effect making the
+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+        GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
+
+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
+    cost of physically performing source distribution, a complete
+    machine-readable copy of the corresponding source code, to be
+    distributed under the terms of Sections 1 and 2 above on a medium
+    customarily used for software interchange; or,
+
+    c) Accompany it with the information you received as to the offer
+    to distribute corresponding source code.  (This alternative is
+    allowed only for noncommercial distribution and only if you
+    received the program in object code or executable form with such
+    an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
+making modifications to it.  For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable.  However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+          NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+         END OF TERMS AND CONDITIONS
+
+      How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.

composer/Plugin/Scaffold/ManageGitIgnore.php

+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\IO\IOInterface;
+
+/**
+ * Manage the .gitignore file.
+ *
+ * @internal
+ */
+class ManageGitIgnore {
+
+  /**
+   * Composer's I/O service.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * The directory where the project is located.
+   *
+   * @var string
+   */
+  protected $dir;
+
+  /**
+   * ManageGitIgnore constructor.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO interface.
+   * @param string $dir
+   *   The directory where the project is located.
+   */
+  public function __construct(IOInterface $io, $dir) {
+    $this->io = $io;
+    $this->dir = $dir;
+  }
+
+  /**
+   * Manages gitignore files.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult[] $files
+   *   A list of scaffold results, each of which holds a path and whether
+   *   or not that file is managed.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions $options
+   *   Configuration options from the composer.json extras section.
+   */
+  public function manageIgnored(array $files, ScaffoldOptions $options) {
+    if (!$this->managementOfGitIgnoreEnabled($options)) {
+      return;
+    }
+
+    // Accumulate entries to add to .gitignore, sorted into buckets based on the
+    // location of the .gitignore file the entry should be added to.
+    $add_to_git_ignore = [];
+    foreach ($files as $scaffoldResult) {
+      $path = $scaffoldResult->destination()->fullPath();
+      $is_ignored = Git::checkIgnore($this->io, $path, $this->dir);
+      if (!$is_ignored) {
+        $is_tracked = Git::checkTracked($this->io, $path, $this->dir);
+        if (!$is_tracked && $scaffoldResult->isManaged()) {
+          $dir = realpath(dirname($path));
+          $name = basename($path);
+          $add_to_git_ignore[$dir][] = '/' . $name;
+        }
+      }
+    }
+    // Write out the .gitignore files one at a time.
+    foreach ($add_to_git_ignore as $dir => $entries) {
+      $this->addToGitIgnore($dir, $entries);
+    }
+  }
+
+  /**
+   * Determines whether we should manage gitignore files.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions $options
+   *   Configuration options from the composer.json extras section.
+   *
+   * @return bool
+   *   Whether or not gitignore files should be managed.
+   */
+  protected function managementOfGitIgnoreEnabled(ScaffoldOptions $options) {
+    // If the composer.json stipulates whether gitignore is managed or not, then
+    // follow its recommendation.
+    if ($options->hasGitIgnore()) {
+      return $options->gitIgnore();
+    }
+
+    // Do not manage .gitignore if there is no repository here.
+    if (!Git::isRepository($this->io, $this->dir)) {
+      return FALSE;
+    }
+
+    // If the composer.json did not specify whether or not .gitignore files
+    // should be managed, then manage them if the vendor directory is ignored.
+    return Git::checkIgnore($this->io, 'vendor', $this->dir);
+  }
+
+  /**
+   * Adds a set of entries to the specified .gitignore file.
+   *
+   * @param string $dir
+   *   Path to directory where gitignore should be written.
+   * @param string[] $entries
+   *   Entries to write to .gitignore file.
+   */
+  protected function addToGitIgnore($dir, array $entries) {
+    sort($entries);
+    $git_ignore_path = $dir . '/.gitignore';
+    $contents = '';
+
+    // Appending to existing .gitignore files.
+    if (file_exists($git_ignore_path)) {
+      $contents = file_get_contents($git_ignore_path);
+      if (!empty($contents) && !str_ends_with($contents, "\n")) {
+        $contents .= "\n";
+      }
+    }
+
+    $contents .= implode("\n", $entries);
+    file_put_contents($git_ignore_path, $contents);
+  }
+
+}