Initial Drupal 11 with DDEV setup

vendor/drupal/core-composer-scaffold/AllowedPackages.php

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+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Composer;
+use Composer\Installer\PackageEvent;
+use Composer\IO\IOInterface;
+use Composer\Package\PackageInterface;
+
+/**
+ * Determine recursively which packages have been allowed to scaffold files.
+ *
+ * If the root-level composer.json allows drupal/core, and drupal/core allows
+ * drupal/assets, then the later package will also implicitly be allowed.
+ *
+ * @internal
+ */
+class AllowedPackages implements PostPackageEventListenerInterface {
+
+  /**
+   * The Composer service.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * Composer's I/O service.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * Manager of the options in the top-level composer.json's 'extra' section.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ManageOptions
+   */
+  protected $manageOptions;
+
+  /**
+   * The list of new packages added by this Composer command.
+   *
+   * @var array
+   */
+  protected $newPackages = [];
+
+  /**
+   * AllowedPackages constructor.
+   *
+   * @param \Composer\Composer $composer
+   *   The composer object.
+   * @param \Composer\IO\IOInterface $io
+   *   IOInterface to write to.
+   * @param \Drupal\Composer\Plugin\Scaffold\ManageOptions $manage_options
+   *   Manager of the options in the top-level composer.json's 'extra' section.
+   */
+  public function __construct(Composer $composer, IOInterface $io, ManageOptions $manage_options) {
+    $this->composer = $composer;
+    $this->io = $io;
+    $this->manageOptions = $manage_options;
+  }
+
+  /**
+   * Gets a list of all packages that are allowed to copy scaffold files.
+   *
+   * We will implicitly allow the projects 'drupal/legacy-scaffold-assets'
+   * and 'drupal/core' to scaffold files, if they are present. Any other
+   * project must be explicitly allowed in the top-level composer.json
+   * file in order to be allowed to override scaffold files.
+   * Configuration for packages specified later will override configuration
+   * specified by packages listed earlier. In other words, the last listed
+   * package has the highest priority. The root package will always be returned
+   * at the end of the list.
+   *
+   * @return \Composer\Package\PackageInterface[]
+   *   An array of allowed Composer packages.
+   */
+  public function getAllowedPackages() {
+    $top_level_packages = $this->getTopLevelAllowedPackages();
+    $allowed_packages = $this->recursiveGetAllowedPackages($top_level_packages);
+    // If the root package defines any file mappings, then implicitly add it
+    // to the list of allowed packages. Add it at the end so that it overrides
+    // all the preceding packages.
+    if ($this->manageOptions->getOptions()->hasFileMapping()) {
+      $root_package = $this->composer->getPackage();
+      unset($allowed_packages[$root_package->getName()]);
+      $allowed_packages[$root_package->getName()] = $root_package;
+    }
+    // Handle any newly-added packages that are not already allowed.
+    return $this->evaluateNewPackages($allowed_packages);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function event(PackageEvent $event) {
+    $operation = $event->getOperation();
+    // Determine the package. Later, in evaluateNewPackages(), we will report
+    // which of the newly-installed packages have scaffold operations, and
+    // whether or not they are allowed to scaffold by the allowed-packages
+    // option in the root-level composer.json file.
+    $package = $operation->getOperationType() === 'update' ? $operation->getTargetPackage() : $operation->getPackage();
+    if (ScaffoldOptions::hasOptions($package->getExtra())) {
+      $this->newPackages[$package->getName()] = $package;
+    }
+  }
+
+  /**
+   * Gets all packages that are allowed in the top-level composer.json.
+   *
+   * We will implicitly allow the projects 'drupal/legacy-scaffold-assets'
+   * and 'drupal/core' to scaffold files, if they are present. Any other
+   * project must be explicitly allowed in the top-level composer.json
+   * file in order to be allowed to override scaffold files.
+   *
+   * @return array
+   *   An array of allowed Composer package names.
+   */
+  protected function getTopLevelAllowedPackages() {
+    $implicit_packages = [
+      'drupal/legacy-scaffold-assets',
+      'drupal/core',
+    ];
+    $top_level_packages = $this->manageOptions->getOptions()->allowedPackages();
+    return array_merge($implicit_packages, $top_level_packages);
+  }
+
+  /**
+   * Builds a name-to-package mapping from a list of package names.
+   *
+   * @param string[] $packages_to_allow
+   *   List of package names to allow.
+   * @param array $allowed_packages
+   *   Mapping of package names to PackageInterface of packages already
+   *   accumulated.
+   *
+   * @return \Composer\Package\PackageInterface[]
+   *   Mapping of package names to PackageInterface in priority order.
+   */
+  protected function recursiveGetAllowedPackages(array $packages_to_allow, array $allowed_packages = []) {
+    foreach ($packages_to_allow as $name) {
+      $package = $this->getPackage($name);
+      if ($package instanceof PackageInterface && !isset($allowed_packages[$name])) {
+        $allowed_packages[$name] = $package;
+        $package_options = $this->manageOptions->packageOptions($package);
+        $allowed_packages = $this->recursiveGetAllowedPackages($package_options->allowedPackages(), $allowed_packages);
+      }
+    }
+    return $allowed_packages;
+  }
+
+  /**
+   * Evaluates newly-added packages and see if they are already allowed.
+   *
+   * For now we will only emit warnings if they are not.
+   *
+   * @param array $allowed_packages
+   *   Mapping of package names to PackageInterface of packages already
+   *   accumulated.
+   *
+   * @return \Composer\Package\PackageInterface[]
+   *   Mapping of package names to PackageInterface in priority order.
+   */
+  protected function evaluateNewPackages(array $allowed_packages) {
+    foreach ($this->newPackages as $name => $newPackage) {
+      if (!array_key_exists($name, $allowed_packages)) {
+        $this->io->write("Not scaffolding files for <comment>{$name}</comment>, because it is not listed in the element 'extra.drupal-scaffold.allowed-packages' in the root-level composer.json file.");
+      }
+      else {
+        $this->io->write("Package <comment>{$name}</comment> has scaffold operations, and is already allowed in the root-level composer.json file.");
+      }
+    }
+    // @todo We could prompt the user and ask if they wish to allow a
+    // newly-added package. This might be useful if, for example, the user
+    // might wish to require an installation profile that contains scaffolded
+    // assets. For more information, see:
+    // https://www.drupal.org/project/drupal/issues/3064990
+    return $allowed_packages;
+  }
+
+  /**
+   * Retrieves a package from the current composer process.
+   *
+   * @param string $name
+   *   Name of the package to get from the current composer installation.
+   *
+   * @return \Composer\Package\PackageInterface|null
+   *   The Composer package.
+   */
+  protected function getPackage($name) {
+    return $this->composer->getRepositoryManager()->getLocalRepository()->findPackage($name, '*');
+  }
+
+}

vendor/drupal/core-composer-scaffold/CommandProvider.php

@@ -0,0 +1,21 @@
+<?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()];
+  }
+
+}

vendor/drupal/core-composer-scaffold/ComposerScaffoldCommand.php

@@ -0,0 +1,56 @@
+<?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;
+  }
+
+}

vendor/drupal/core-composer-scaffold/GenerateAutoloadReferenceFile.php

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+<?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;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Git.php

@@ -0,0 +1,81 @@
+<?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;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Handler.php

@@ -0,0 +1,248 @@
+<?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();
+  }
+
+}

vendor/drupal/core-composer-scaffold/Interpolator.php

@@ -0,0 +1,157 @@
+<?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;
+  }
+
+}

vendor/drupal/core-composer-scaffold/LICENSE.txt

@@ -0,0 +1,339 @@
+        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.

vendor/drupal/core-composer-scaffold/ManageGitIgnore.php

@@ -0,0 +1,127 @@
+<?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);
+  }
+
+}

vendor/drupal/core-composer-scaffold/ManageOptions.php

@@ -0,0 +1,92 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Composer;
+use Composer\Package\PackageInterface;
+use Composer\Util\Filesystem;
+
+/**
+ * Per-project options from the 'extras' section of the composer.json file.
+ *
+ * Projects that describe scaffold files do so via their scaffold options.
+ * This data is pulled from the 'drupal-scaffold' portion of the extras
+ * section of the project data.
+ *
+ * @internal
+ */
+class ManageOptions {
+
+  /**
+   * The Composer service.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * ManageOptions constructor.
+   *
+   * @param \Composer\Composer $composer
+   *   The Composer service.
+   */
+  public function __construct(Composer $composer) {
+    $this->composer = $composer;
+  }
+
+  /**
+   * Gets the root-level scaffold options for this project.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions
+   *   The scaffold options object.
+   */
+  public function getOptions() {
+    return $this->packageOptions($this->composer->getPackage());
+  }
+
+  /**
+   * Gets the scaffold options for the stipulated project.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package to fetch the scaffold options from.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions
+   *   The scaffold options object.
+   */
+  public function packageOptions(PackageInterface $package) {
+    return ScaffoldOptions::create($package->getExtra());
+  }
+
+  /**
+   * Creates an interpolator for the 'locations' element.
+   *
+   * The interpolator returned will replace a path string with the tokens
+   * defined in the 'locations' element.
+   *
+   * Note that only the root package may define locations.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Interpolator
+   *   Interpolator that will do replacements in a string using tokens in
+   *   'locations' element.
+   */
+  public function getLocationReplacements() {
+    return (new Interpolator())->setData($this->ensureLocations());
+  }
+
+  /**
+   * Ensures that all of the locations defined in the scaffold files exist.
+   *
+   * Create them on the filesystem if they do not.
+   */
+  protected function ensureLocations() {
+    $fs = new Filesystem();
+    $locations = $this->getOptions()->locations() + ['web_root' => './'];
+    $locations = array_map(function ($location) use ($fs) {
+      $fs->ensureDirectoryExists($location);
+      $location = realpath($location);
+      return $location;
+    }, $locations);
+    return $locations;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/AbstractOperation.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+
+/**
+ * Provides default behaviors for operations.
+ *
+ * @internal
+ */
+abstract class AbstractOperation implements OperationInterface {
+
+  /**
+   * Cached contents of scaffold file to be written to disk.
+   *
+   * @var string
+   */
+  protected $contents;
+
+  /**
+   * {@inheritdoc}
+   */
+  final public function contents() {
+    if (!isset($this->contents)) {
+      $this->contents = $this->generateContents();
+    }
+    return $this->contents;
+  }
+
+  /**
+   * Load the scaffold contents or otherwise generate what is needed.
+   *
+   * @return string
+   *   The contents of the scaffold file.
+   */
+  abstract protected function generateContents();
+
+  /**
+   * {@inheritdoc}
+   */
+  public function scaffoldOverExistingTarget(OperationInterface $existing_target) {
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function scaffoldAtNewLocation(ScaffoldFilePath $destination) {
+    return $this;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/AppendOp.php

@@ -0,0 +1,216 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Composer\IO\IOInterface;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldOptions;
+
+/**
+ * Scaffold operation to add to the beginning and/or end of a scaffold file.
+ *
+ * @internal
+ */
+class AppendOp extends AbstractOperation {
+
+  /**
+   * Identifies Append operations.
+   */
+  const ID = 'append';
+
+  /**
+   * Path to the source file to prepend, if any.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   */
+  protected $prepend;
+
+  /**
+   * Path to the source file to append, if any.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   */
+  protected $append;
+
+  /**
+   * Path to the default data to use when appending to an empty file.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   */
+  protected $default;
+
+  /**
+   * An indicator of whether the file we are appending to is managed or not.
+   *
+   * @var bool
+   */
+  protected $managed;
+
+  /**
+   * An indicator of whether we are allowed to append to a non-scaffolded file.
+   *
+   * @var bool
+   */
+  protected $forceAppend;
+
+  /**
+   * The contents from the file that we are prepending / appending to.
+   *
+   * @var string
+   */
+  protected $originalContents;
+
+  /**
+   * Constructs an AppendOp.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath|null $prepend_path
+   *   (optional) The relative path to the prepend file.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath|null $append_path
+   *   (optional) The relative path to the append file.
+   * @param bool $force_append
+   *   (optional) TRUE if is okay to append to a file that was not scaffolded.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath|null $default_path
+   *   (optional) The relative path to the default data.
+   */
+  public function __construct(
+    ?ScaffoldFilePath $prepend_path = NULL,
+    ?ScaffoldFilePath $append_path = NULL,
+    $force_append = FALSE,
+    ?ScaffoldFilePath $default_path = NULL,
+  ) {
+    $this->forceAppend = $force_append;
+    $this->prepend = $prepend_path;
+    $this->append = $append_path;
+    $this->default = $default_path;
+    $this->managed = TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function generateContents() {
+    // Fetch the prepend contents, if provided.
+    $prepend_contents = '';
+    if (!empty($this->prepend)) {
+      $prepend_contents = file_get_contents($this->prepend->fullPath()) . "\n";
+    }
+    // Fetch the append contents, if provided.
+    $append_contents = '';
+    if (!empty($this->append)) {
+      $append_contents = "\n" . file_get_contents($this->append->fullPath());
+    }
+
+    // Get the original contents, or the default data if the original is empty.
+    $original_contents = $this->originalContents;
+    if (empty($original_contents) && !empty($this->default)) {
+      $original_contents = file_get_contents($this->default->fullPath());
+    }
+
+    // Attach it all together.
+    return $prepend_contents . $original_contents . $append_contents;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function process(ScaffoldFilePath $destination, IOInterface $io, ScaffoldOptions $options) {
+    $destination_path = $destination->fullPath();
+    $interpolator = $destination->getInterpolator();
+
+    // Be extra-noisy of creating a new file or appending to a non-scaffold
+    // file. Note that if the file already has the append contents, then the
+    // OperationFactory will make a SkipOp instead, and we will not get here.
+    if (!$this->managed) {
+      $message = '  - <info>NOTICE</info> Modifying existing file at <info>[dest-rel-path]</info>.';
+      if (!file_exists($destination_path)) {
+        $message = '  - <info>NOTICE</info> Creating a new file at <info>[dest-rel-path]</info>.';
+      }
+      $message .= ' Examine the contents and ensure that it came out correctly.';
+      $io->write($interpolator->interpolate($message));
+    }
+
+    // Notify that we are prepending, if there is prepend data.
+    if (!empty($this->prepend)) {
+      $this->prepend->addInterpolationData($interpolator, 'prepend');
+      $io->write($interpolator->interpolate("  - Prepend to <info>[dest-rel-path]</info> from <info>[prepend-rel-path]</info>"));
+    }
+    // Notify that we are appending, if there is append data.
+    if (!empty($this->append)) {
+      $this->append->addInterpolationData($interpolator, 'append');
+      $io->write($interpolator->interpolate("  - Append to <info>[dest-rel-path]</info> from <info>[append-rel-path]</info>"));
+    }
+
+    // Write the resulting data
+    file_put_contents($destination_path, $this->contents());
+
+    // Return a ScaffoldResult with knowledge of whether this file is managed.
+    return new ScaffoldResult($destination, $this->managed);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function scaffoldOverExistingTarget(OperationInterface $existing_target) {
+    $this->originalContents = $existing_target->contents();
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function scaffoldAtNewLocation(ScaffoldFilePath $destination) {
+    // If there is no existing scaffold file at the target location, then any
+    // append we do will be to an unmanaged file.
+    $this->managed = FALSE;
+
+    // Default: do not allow an append over a file that was not scaffolded.
+    if (!$this->forceAppend) {
+      $message = "  - Skip <info>[dest-rel-path]</info>: cannot append to a path that was not scaffolded unless 'force-append' property is set.";
+      return new SkipOp($message);
+    }
+
+    // If the target file does not exist, then we will allow the append to
+    // happen if we have default data to provide for it.
+    if (!file_exists($destination->fullPath())) {
+      if (!empty($this->default)) {
+        return $this;
+      }
+      $message = "  - Skip <info>[dest-rel-path]</info>: no file exists at the target path, and no default data provided.";
+      return new SkipOp($message);
+    }
+
+    // If the target file DOES exist, and it already contains the append/prepend
+    // data, then we will skip the operation.
+    $existingData = file_get_contents($destination->fullPath());
+    if ($this->existingFileHasData($existingData, $this->append) || $this->existingFileHasData($existingData, $this->prepend)) {
+      $message = "  - Skip <info>[dest-rel-path]</info>: the file already has the append/prepend data.";
+      return new SkipOp($message);
+    }
+
+    // Cache the original data to use during append.
+    $this->originalContents = $existingData;
+
+    return $this;
+  }
+
+  /**
+   * Check to see if the append/prepend data has already been applied.
+   *
+   * @param string $contents
+   *   The contents of the target file.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $data_path
+   *   The path to the data to append or prepend.
+   *
+   * @return bool
+   *   'TRUE' if the append/prepend data already exists in contents.
+   */
+  protected function existingFileHasData($contents, $data_path) {
+    if (empty($data_path)) {
+      return FALSE;
+    }
+    $data = file_get_contents($data_path->fullPath());
+
+    return str_contains($contents, $data);
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/OperationData.php

@@ -0,0 +1,229 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+/**
+ * Holds parameter data for operation objects during operation creation only.
+ *
+ * @internal
+ */
+class OperationData {
+
+  const MODE = 'mode';
+  const PATH = 'path';
+  const OVERWRITE = 'overwrite';
+  const PREPEND = 'prepend';
+  const APPEND = 'append';
+  const DEFAULT = 'default';
+  const FORCE_APPEND = 'force-append';
+
+  /**
+   * The parameter data.
+   *
+   * @var array
+   */
+  protected $data;
+
+  /**
+   * The destination path.
+   *
+   * @var string
+   */
+  protected $destination;
+
+  /**
+   * OperationData constructor.
+   *
+   * @param string $destination
+   *   The destination path.
+   * @param mixed $data
+   *   The raw data array to wrap.
+   */
+  public function __construct($destination, $data) {
+    $this->destination = $destination;
+    $this->data = $this->normalizeScaffoldMetadata($destination, $data);
+  }
+
+  /**
+   * Gets the destination path that this operation data is associated with.
+   *
+   * @return string
+   *   The destination path for the scaffold result.
+   */
+  public function destination() {
+    return $this->destination;
+  }
+
+  /**
+   * Gets operation mode.
+   *
+   * @return string
+   *   Operation mode.
+   */
+  public function mode() {
+    return $this->data[self::MODE];
+  }
+
+  /**
+   * Checks if path exists.
+   *
+   * @return bool
+   *   Returns true if path exists
+   */
+  public function hasPath() {
+    return isset($this->data[self::PATH]);
+  }
+
+  /**
+   * Gets path.
+   *
+   * @return string
+   *   The path.
+   */
+  public function path() {
+    return $this->data[self::PATH];
+  }
+
+  /**
+   * Determines overwrite.
+   *
+   * @return bool
+   *   Returns true if overwrite mode was selected.
+   */
+  public function overwrite() {
+    return !empty($this->data[self::OVERWRITE]);
+  }
+
+  /**
+   * Determines whether 'force-append' has been set.
+   *
+   * @return bool
+   *   Returns true if 'force-append' mode was selected.
+   */
+  public function forceAppend() {
+    if ($this->hasDefault()) {
+      return TRUE;
+    }
+    return !empty($this->data[self::FORCE_APPEND]);
+  }
+
+  /**
+   * Checks if prepend path exists.
+   *
+   * @return bool
+   *   Returns true if prepend exists.
+   */
+  public function hasPrepend() {
+    return isset($this->data[self::PREPEND]);
+  }
+
+  /**
+   * Gets prepend path.
+   *
+   * @return string
+   *   Path to prepend data
+   */
+  public function prepend() {
+    return $this->data[self::PREPEND];
+  }
+
+  /**
+   * Checks if append path exists.
+   *
+   * @return bool
+   *   Returns true if prepend exists.
+   */
+  public function hasAppend() {
+    return isset($this->data[self::APPEND]);
+  }
+
+  /**
+   * Gets append path.
+   *
+   * @return string
+   *   Path to append data
+   */
+  public function append() {
+    return $this->data[self::APPEND];
+  }
+
+  /**
+   * Checks if default path exists.
+   *
+   * @return bool
+   *   Returns true if there is default data available.
+   */
+  public function hasDefault() {
+    return isset($this->data[self::DEFAULT]);
+  }
+
+  /**
+   * Gets default path.
+   *
+   * @return string
+   *   Path to default data
+   */
+  public function default() {
+    return $this->data[self::DEFAULT];
+  }
+
+  /**
+   * Normalizes metadata by converting literal values into arrays.
+   *
+   * Conversions performed include:
+   *   - Boolean 'false' means "skip".
+   *   - A string means "replace", with the string value becoming the path.
+   *
+   * @param string $destination
+   *   The destination path for the scaffold file.
+   * @param mixed $value
+   *   The metadata for this operation object, which varies by operation type.
+   *
+   * @return array
+   *   Normalized scaffold metadata with default values.
+   */
+  protected function normalizeScaffoldMetadata($destination, $value) {
+    $defaultScaffoldMetadata = [
+      self::MODE => ReplaceOp::ID,
+      self::PREPEND => NULL,
+      self::APPEND => NULL,
+      self::DEFAULT => NULL,
+      self::OVERWRITE => TRUE,
+    ];
+
+    return $this->convertScaffoldMetadata($destination, $value) + $defaultScaffoldMetadata;
+  }
+
+  /**
+   * Performs the conversion-to-array step in normalizeScaffoldMetadata.
+   *
+   * @param string $destination
+   *   The destination path for the scaffold file.
+   * @param mixed $value
+   *   The metadata for this operation object, which varies by operation type.
+   *
+   * @return array
+   *   Normalized scaffold metadata.
+   */
+  protected function convertScaffoldMetadata($destination, $value) {
+    if (is_bool($value)) {
+      if (!$value) {
+        return [self::MODE => SkipOp::ID];
+      }
+      throw new \RuntimeException("File mapping {$destination} cannot be given the value 'true'.");
+    }
+    if (empty($value)) {
+      throw new \RuntimeException("File mapping {$destination} cannot be empty.");
+    }
+    if (is_string($value)) {
+      $value = [self::PATH => $value];
+    }
+    // If there is no 'mode', but there is an 'append' or a 'prepend' path,
+    // then the mode is 'append' (append + prepend).
+    if (!isset($value[self::MODE]) && (isset($value[self::APPEND]) || isset($value[self::PREPEND]))) {
+      $value[self::MODE] = AppendOp::ID;
+    }
+    return $value;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/OperationFactory.php

@@ -0,0 +1,162 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Composer\Composer;
+use Composer\Package\PackageInterface;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+
+/**
+ * Create Scaffold operation objects based on provided metadata.
+ *
+ * @internal
+ */
+class OperationFactory {
+
+  /**
+   * The Composer service.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * OperationFactory constructor.
+   *
+   * @param \Composer\Composer $composer
+   *   Reference to the 'Composer' object, since the Scaffold Operation Factory
+   *   is also responsible for evaluating relative package paths as it creates
+   *   scaffold operations.
+   */
+  public function __construct(Composer $composer) {
+    $this->composer = $composer;
+  }
+
+  /**
+   * Creates a scaffolding operation object as determined by the metadata.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package that relative paths will be relative from.
+   * @param OperationData $operation_data
+   *   The parameter data for this operation object; varies by operation type.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface
+   *   The scaffolding operation object (skip, replace, etc.)
+   *
+   * @throws \RuntimeException
+   *   Exception thrown when parameter data does not identify a known scaffold
+   *   operation.
+   */
+  public function create(PackageInterface $package, OperationData $operation_data) {
+    switch ($operation_data->mode()) {
+      case SkipOp::ID:
+        return new SkipOp();
+
+      case ReplaceOp::ID:
+        return $this->createReplaceOp($package, $operation_data);
+
+      case AppendOp::ID:
+        return $this->createAppendOp($package, $operation_data);
+    }
+    throw new \RuntimeException("Unknown scaffold operation mode <comment>{$operation_data->mode()}</comment>.");
+  }
+
+  /**
+   * Creates a 'replace' scaffold op.
+   *
+   * Replace ops may copy or symlink, depending on settings.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package that relative paths will be relative from.
+   * @param OperationData $operation_data
+   *   The parameter data for this operation object, i.e. the relative 'path'.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface
+   *   A scaffold replace operation object.
+   */
+  protected function createReplaceOp(PackageInterface $package, OperationData $operation_data) {
+    if (!$operation_data->hasPath()) {
+      throw new \RuntimeException("'path' component required for 'replace' operations.");
+    }
+    $package_name = $package->getName();
+    $package_path = $this->getPackagePath($package);
+    $source = ScaffoldFilePath::sourcePath($package_name, $package_path, $operation_data->destination(), $operation_data->path());
+    $op = new ReplaceOp($source, $operation_data->overwrite());
+    return $op;
+  }
+
+  /**
+   * Creates an 'append' (or 'prepend') scaffold op.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package that relative paths will be relative from.
+   * @param OperationData $operation_data
+   *   The parameter data for this operation object, i.e. the relative 'path'.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface
+   *   A scaffold replace operation object.
+   */
+  protected function createAppendOp(PackageInterface $package, OperationData $operation_data) {
+    $package_name = $package->getName();
+    $package_path = $this->getPackagePath($package);
+    $prepend_source_file = NULL;
+    $append_source_file = NULL;
+    $default_data_file = NULL;
+    if ($operation_data->hasPrepend()) {
+      $prepend_source_file = ScaffoldFilePath::sourcePath($package_name, $package_path, $operation_data->destination(), $operation_data->prepend());
+    }
+    if ($operation_data->hasAppend()) {
+      $append_source_file = ScaffoldFilePath::sourcePath($package_name, $package_path, $operation_data->destination(), $operation_data->append());
+    }
+    if ($operation_data->hasDefault()) {
+      $default_data_file = ScaffoldFilePath::sourcePath($package_name, $package_path, $operation_data->destination(), $operation_data->default());
+    }
+    if (!$this->hasContent($prepend_source_file) && !$this->hasContent($append_source_file)) {
+      $message = '  - Keep <info>[dest-rel-path]</info> unchanged: no content to prepend / append was provided.';
+      return new SkipOp($message);
+    }
+
+    return new AppendOp($prepend_source_file, $append_source_file, $operation_data->forceAppend(), $default_data_file);
+  }
+
+  /**
+   * Checks to see if the specified scaffold file exists and has content.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath|null $file
+   *   (optional) Scaffold file to check.
+   *
+   * @return bool
+   *   True if the file exists and has content.
+   */
+  protected function hasContent(?ScaffoldFilePath $file = NULL) {
+    if (!$file) {
+      return FALSE;
+    }
+    $path = $file->fullPath();
+    return is_file($path) && (filesize($path) > 0);
+  }
+
+  /**
+   * Gets the file path of a package.
+   *
+   * Note that if we call getInstallPath on the root package, we get the
+   * wrong answer (the installation manager thinks our package is in
+   * vendor). We therefore add special checking for this case.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package.
+   *
+   * @return string
+   *   The file path.
+   */
+  protected function getPackagePath(PackageInterface $package) {
+    if ($package->getName() == $this->composer->getPackage()->getName()) {
+      // This will respect the --working-dir option if Composer is invoked with
+      // it. There is no API or method to determine the filesystem path of
+      // a package's composer.json file.
+      return getcwd();
+    }
+    return $this->composer->getInstallationManager()->getInstallPath($package);
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/OperationInterface.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Composer\IO\IOInterface;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldOptions;
+
+/**
+ * Interface for scaffold operation objects.
+ *
+ * @internal
+ */
+interface OperationInterface {
+
+  /**
+   * Returns the exact data that will be written to the scaffold files.
+   *
+   * @return string
+   *   Data to be written to the scaffold location.
+   */
+  public function contents();
+
+  /**
+   * Process this scaffold operation.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $destination
+   *   Scaffold file's destination path.
+   * @param \Composer\IO\IOInterface $io
+   *   IOInterface to write to.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions $options
+   *   Various options that may alter the behavior of the operation.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult
+   *   Result of the scaffolding operation.
+   */
+  public function process(ScaffoldFilePath $destination, IOInterface $io, ScaffoldOptions $options);
+
+  /**
+   * Determines what to do if operation is used at same path as a previous op.
+   *
+   * Default behavior is to scaffold this operation at the specified
+   * destination, ignoring whatever was there before.
+   *
+   * @param OperationInterface $existing_target
+   *   Existing file at the destination path that we should combine with.
+   *
+   * @return OperationInterface
+   *   The op to use at this destination.
+   */
+  public function scaffoldOverExistingTarget(OperationInterface $existing_target);
+
+  /**
+   * Determines what to do if operation is used without a previous operation.
+   *
+   * Default behavior is to scaffold this operation at the specified
+   * destination. Most operations overwrite rather than modify existing files,
+   * and therefore do not need to do anything special when there is no existing
+   * file.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $destination
+   *   Scaffold file's destination path.
+   *
+   * @return OperationInterface
+   *   The op to use at this destination.
+   */
+  public function scaffoldAtNewLocation(ScaffoldFilePath $destination);
+
+}

vendor/drupal/core-composer-scaffold/Operations/ReplaceOp.php

@@ -0,0 +1,126 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Composer\IO\IOInterface;
+use Composer\Util\Filesystem;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldOptions;
+
+/**
+ * Scaffold operation to copy or symlink from source to destination.
+ *
+ * @internal
+ */
+class ReplaceOp extends AbstractOperation {
+
+  /**
+   * Identifies Replace operations.
+   */
+  const ID = 'replace';
+
+  /**
+   * The relative path to the source file.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   */
+  protected $source;
+
+  /**
+   * Whether to overwrite existing files.
+   *
+   * @var bool
+   */
+  protected $overwrite;
+
+  /**
+   * Constructs a ReplaceOp.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $sourcePath
+   *   The relative path to the source file.
+   * @param bool $overwrite
+   *   Whether to allow this scaffold file to overwrite files already at
+   *   the destination. Defaults to TRUE.
+   */
+  public function __construct(ScaffoldFilePath $sourcePath, $overwrite = TRUE) {
+    $this->source = $sourcePath;
+    $this->overwrite = $overwrite;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function generateContents() {
+    return file_get_contents($this->source->fullPath());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function process(ScaffoldFilePath $destination, IOInterface $io, ScaffoldOptions $options) {
+    $fs = new Filesystem();
+    $destination_path = $destination->fullPath();
+    // Do nothing if overwrite is 'false' and a file already exists at the
+    // destination.
+    if ($this->overwrite === FALSE && file_exists($destination_path)) {
+      $interpolator = $destination->getInterpolator();
+      $io->write($interpolator->interpolate("  - Skip <info>[dest-rel-path]</info> because it already exists and overwrite is <comment>false</comment>."));
+      return new ScaffoldResult($destination, FALSE);
+    }
+
+    // Get rid of the destination if it exists, and make sure that
+    // the directory where it's going to be placed exists.
+    $fs->remove($destination_path);
+    $fs->ensureDirectoryExists(dirname($destination_path));
+    if ($options->symlink()) {
+      return $this->symlinkScaffold($destination, $io);
+    }
+    return $this->copyScaffold($destination, $io);
+  }
+
+  /**
+   * Copies the scaffold file.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $destination
+   *   Scaffold file to process.
+   * @param \Composer\IO\IOInterface $io
+   *   IOInterface to writing to.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult
+   *   The scaffold result.
+   */
+  protected function copyScaffold(ScaffoldFilePath $destination, IOInterface $io) {
+    $interpolator = $destination->getInterpolator();
+    $this->source->addInterpolationData($interpolator);
+    if (file_put_contents($destination->fullPath(), $this->contents()) === FALSE) {
+      throw new \RuntimeException($interpolator->interpolate("Could not copy source file <info>[src-rel-path]</info> to <info>[dest-rel-path]</info>!"));
+    }
+    $io->write($interpolator->interpolate("  - Copy <info>[dest-rel-path]</info> from <info>[src-rel-path]</info>"));
+    return new ScaffoldResult($destination, $this->overwrite);
+  }
+
+  /**
+   * Symlinks the scaffold file.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $destination
+   *   Scaffold file to process.
+   * @param \Composer\IO\IOInterface $io
+   *   IOInterface to writing to.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult
+   *   The scaffold result.
+   */
+  protected function symlinkScaffold(ScaffoldFilePath $destination, IOInterface $io) {
+    $interpolator = $destination->getInterpolator();
+    try {
+      $fs = new Filesystem();
+      $fs->relativeSymlink($this->source->fullPath(), $destination->fullPath());
+    }
+    catch (\Exception $e) {
+      throw new \RuntimeException($interpolator->interpolate("Could not symlink source file <info>[src-rel-path]</info> to <info>[dest-rel-path]</info>!"), [], $e);
+    }
+    $io->write($interpolator->interpolate("  - Link <info>[dest-rel-path]</info> from <info>[src-rel-path]</info>"));
+    return new ScaffoldResult($destination, $this->overwrite);
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/ScaffoldFileCollection.php

@@ -0,0 +1,198 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Composer\IO\IOInterface;
+use Drupal\Composer\Plugin\Scaffold\Interpolator;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFileInfo;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldOptions;
+
+/**
+ * Collection of scaffold files.
+ *
+ * @internal
+ */
+class ScaffoldFileCollection implements \IteratorAggregate {
+
+  /**
+   * Nested list of all scaffold files.
+   *
+   * The top level array maps from the package name to the collection of
+   * scaffold files provided by that package. Each collection of scaffold files
+   * is keyed by destination path.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFileInfo[][]
+   */
+  protected $scaffoldFilesByProject = [];
+
+  /**
+   * ScaffoldFileCollection constructor.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface[][] $file_mappings
+   *   A multidimensional array of file mappings.
+   * @param \Drupal\Composer\Plugin\Scaffold\Interpolator $location_replacements
+   *   An object with the location mappings (e.g. [web-root]).
+   */
+  public function __construct(array $file_mappings, Interpolator $location_replacements) {
+    // Collection of all destination paths to be scaffolded. Used to determine
+    // when two projects scaffold the same file and we have to either replace or
+    // combine them together.
+    // @see OperationInterface::scaffoldOverExistingTarget().
+    $scaffoldFiles = [];
+
+    // Build the list of ScaffoldFileInfo objects by project.
+    foreach ($file_mappings as $package_name => $package_file_mappings) {
+      foreach ($package_file_mappings as $destination_rel_path => $op) {
+        $destination = ScaffoldFilePath::destinationPath($package_name, $destination_rel_path, $location_replacements);
+
+        // If there was already a scaffolding operation happening at this path,
+        // allow the new operation to decide how to handle the override.
+        // Usually, the new operation will replace whatever was there before.
+        if (isset($scaffoldFiles[$destination_rel_path])) {
+          $previous_scaffold_file = $scaffoldFiles[$destination_rel_path];
+          $op = $op->scaffoldOverExistingTarget($previous_scaffold_file->op());
+
+          // Remove the previous op so we only touch the destination once.
+          $message = "  - Skip <info>[dest-rel-path]</info>: overridden in <comment>{$package_name}</comment>";
+          $this->scaffoldFilesByProject[$previous_scaffold_file->packageName()][$destination_rel_path] = new ScaffoldFileInfo($destination, new SkipOp($message));
+        }
+        // If there is NOT already a scaffolding operation happening at this
+        // path, notify the scaffold operation of this fact.
+        else {
+          $op = $op->scaffoldAtNewLocation($destination);
+        }
+
+        // Combine the scaffold operation with the destination and record it.
+        $scaffold_file = new ScaffoldFileInfo($destination, $op);
+        $scaffoldFiles[$destination_rel_path] = $scaffold_file;
+        $this->scaffoldFilesByProject[$package_name][$destination_rel_path] = $scaffold_file;
+      }
+    }
+  }
+
+  /**
+   * Removes any item that has a path matching any path in the provided list.
+   *
+   * Matching is done via destination path.
+   *
+   * @param string[] $files_to_filter
+   *   List of destination paths.
+   */
+  public function filterFiles(array $files_to_filter) {
+    foreach ($this->scaffoldFilesByProject as $project_name => $scaffold_files) {
+      foreach ($scaffold_files as $destination_rel_path => $scaffold_file) {
+        if (in_array($destination_rel_path, $files_to_filter, TRUE)) {
+          unset($scaffold_files[$destination_rel_path]);
+        }
+      }
+      $this->scaffoldFilesByProject[$project_name] = $scaffold_files;
+      if (!$this->checkListHasItemWithContent($scaffold_files)) {
+        unset($this->scaffoldFilesByProject[$project_name]);
+      }
+    }
+  }
+
+  /**
+   * Scans through a list of scaffold files and determines if any has contents.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFileInfo[] $scaffold_files
+   *   List of scaffold files, path: ScaffoldFileInfo.
+   *
+   * @return bool
+   *   TRUE if at least one item in the list has content
+   */
+  protected function checkListHasItemWithContent(array $scaffold_files) {
+    foreach ($scaffold_files as $scaffold_file) {
+      $contents = $scaffold_file->op()->contents();
+      if (!empty($contents)) {
+        return TRUE;
+      }
+    }
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIterator(): \ArrayIterator {
+    return new \ArrayIterator($this->scaffoldFilesByProject);
+  }
+
+  /**
+   * Processes the files in our collection.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO object.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions $scaffold_options
+   *   The scaffold options.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult[]
+   *   The results array.
+   */
+  public function processScaffoldFiles(IOInterface $io, ScaffoldOptions $scaffold_options) {
+    $results = [];
+    foreach ($this as $project_name => $scaffold_files) {
+      $io->write("Scaffolding files for <comment>{$project_name}</comment>:");
+      foreach ($scaffold_files as $scaffold_file) {
+        $results[$scaffold_file->destination()->relativePath()] = $scaffold_file->process($io, $scaffold_options);
+      }
+    }
+    return $results;
+  }
+
+  /**
+   * Processes the iterator created by ScaffoldFileCollection::create().
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldFileCollection $collection
+   *   The iterator to process.
+   * @param \Composer\IO\IOInterface $io
+   *   The Composer IO object.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions $scaffold_options
+   *   The scaffold options.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult[]
+   *   The results array.
+   *
+   * @deprecated. Called when upgrading from the Core Composer Scaffold plugin
+   *   version 8.8.x due to a bug in the plugin and handler classes. Do not use
+   *   in 8.9.x or 9.x, and remove in Drupal 10.x.
+   */
+  public static function process(ScaffoldFileCollection $collection, IOInterface $io, ScaffoldOptions $scaffold_options) {
+    $results = [];
+    foreach ($collection as $project_name => $scaffold_files) {
+      $io->write("Scaffolding files for <comment>{$project_name}</comment>:");
+      foreach ($scaffold_files as $scaffold_file) {
+        $results[$scaffold_file->destination()->relativePath()] = $scaffold_file->process($io, $scaffold_options);
+      }
+    }
+    return $results;
+  }
+
+  /**
+   * Returns the list of files that have not changed since they were scaffolded.
+   *
+   * Note that there are two reasons a file may have changed:
+   *   - The user modified it after it was scaffolded.
+   *   - The package the file came to was updated, and the file is different in
+   *     the new version.
+   *
+   * With the current scaffold code, we cannot tell the difference between the
+   * two. @see https://www.drupal.org/project/drupal/issues/3092563
+   *
+   * @return string[]
+   *   List of relative paths to unchanged files on disk.
+   */
+  public function checkUnchanged() {
+    $results = [];
+    foreach ($this as $scaffold_files) {
+      foreach ($scaffold_files as $scaffold_file) {
+        if (!$scaffold_file->hasChanged()) {
+          $results[] = $scaffold_file->destination()->relativePath();
+        }
+      }
+    }
+    return $results;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/ScaffoldResult.php

@@ -0,0 +1,61 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+
+/**
+ * Record the result of a scaffold operation.
+ *
+ * @internal
+ */
+class ScaffoldResult {
+
+  /**
+   * The path to the scaffold file that was processed.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   */
+  protected $destination;
+
+  /**
+   * Indicates if this scaffold file is managed by the scaffold command.
+   *
+   * @var bool
+   */
+  protected $managed;
+
+  /**
+   * ScaffoldResult constructor.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $destination
+   *   The path to the scaffold file that was processed.
+   * @param bool $isManaged
+   *   (optional) Whether this result is managed. Defaults to FALSE.
+   */
+  public function __construct(ScaffoldFilePath $destination, $isManaged = FALSE) {
+    $this->destination = $destination;
+    $this->managed = $isManaged;
+  }
+
+  /**
+   * Determines whether this scaffold file is managed.
+   *
+   * @return bool
+   *   TRUE if this scaffold file is managed, FALSE if not.
+   */
+  public function isManaged() {
+    return $this->managed;
+  }
+
+  /**
+   * Gets the destination scaffold file that this result refers to.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   *   The destination path for the scaffold result.
+   */
+  public function destination() {
+    return $this->destination;
+  }
+
+}

vendor/drupal/core-composer-scaffold/Operations/SkipOp.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold\Operations;
+
+use Composer\IO\IOInterface;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath;
+use Drupal\Composer\Plugin\Scaffold\ScaffoldOptions;
+
+/**
+ * Scaffold operation to skip a scaffold file (do nothing).
+ *
+ * @internal
+ */
+class SkipOp extends AbstractOperation {
+
+  /**
+   * Identifies Skip operations.
+   */
+  const ID = 'skip';
+
+  /**
+   * The message to output while processing.
+   *
+   * @var string
+   */
+  protected $message;
+
+  /**
+   * SkipOp constructor.
+   *
+   * @param string $message
+   *   (optional) A custom message to output while skipping.
+   */
+  public function __construct($message = "  - Skip <info>[dest-rel-path]</info>: disabled") {
+    $this->message = $message;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function generateContents() {
+    return '';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function process(ScaffoldFilePath $destination, IOInterface $io, ScaffoldOptions $options) {
+    $interpolator = $destination->getInterpolator();
+    $io->write($interpolator->interpolate($this->message));
+    return new ScaffoldResult($destination, FALSE);
+  }
+
+}

vendor/drupal/core-composer-scaffold/Plugin.php

@@ -0,0 +1,149 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Composer;
+use Composer\EventDispatcher\EventSubscriberInterface;
+use Composer\IO\IOInterface;
+use Composer\Installer\PackageEvent;
+use Composer\Installer\PackageEvents;
+use Composer\Plugin\Capability\CommandProvider;
+use Composer\Plugin\Capable;
+use Composer\Plugin\CommandEvent;
+use Composer\Plugin\PluginEvents;
+use Composer\Plugin\PluginInterface;
+use Composer\Script\Event;
+use Composer\Script\ScriptEvents;
+use Drupal\Composer\Plugin\Scaffold\CommandProvider as ScaffoldCommandProvider;
+
+/**
+ * Composer plugin for handling drupal scaffold.
+ *
+ * @internal
+ */
+class Plugin implements PluginInterface, EventSubscriberInterface, Capable {
+
+  /**
+   * The Composer service.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * Composer's I/O service.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * The Composer Scaffold handler.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\Handler
+   */
+  protected $handler;
+
+  /**
+   * Record whether the 'require' command was called.
+   *
+   * @var bool
+   */
+  protected $requireWasCalled;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function activate(Composer $composer, IOInterface $io) {
+    $this->composer = $composer;
+    $this->io = $io;
+    $this->requireWasCalled = FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deactivate(Composer $composer, IOInterface $io) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function uninstall(Composer $composer, IOInterface $io) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCapabilities() {
+    return [CommandProvider::class => ScaffoldCommandProvider::class];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    // Important note: We only instantiate our handler on "post" events.
+    return [
+      ScriptEvents::POST_UPDATE_CMD => 'postCmd',
+      ScriptEvents::POST_INSTALL_CMD => 'postCmd',
+      PackageEvents::POST_PACKAGE_INSTALL => 'postPackage',
+      PluginEvents::COMMAND => 'onCommand',
+    ];
+  }
+
+  /**
+   * Post command event callback.
+   *
+   * @param \Composer\Script\Event $event
+   *   The Composer event.
+   */
+  public function postCmd(Event $event) {
+    $this->handler()->scaffold();
+  }
+
+  /**
+   * Post package event behavior.
+   *
+   * @param \Composer\Installer\PackageEvent $event
+   *   Composer package event sent on install/update/remove.
+   */
+  public function postPackage(PackageEvent $event) {
+    $this->handler()->onPostPackageEvent($event);
+  }
+
+  /**
+   * Pre command event callback.
+   *
+   * @param \Composer\Plugin\CommandEvent $event
+   *   The Composer command event.
+   */
+  public function onCommand(CommandEvent $event) {
+    if ($event->getCommandName() == 'require') {
+      if ($this->handler) {
+        throw new \Error('Core Scaffold Plugin handler instantiated too early. See https://www.drupal.org/project/drupal/issues/3104922');
+      }
+      $this->requireWasCalled = TRUE;
+    }
+  }
+
+  /**
+   * Instantiates the handler object upon demand.
+   *
+   * It is dangerous to update a Composer plugin if it loads any classes prior
+   * to the `composer update` operation, and later tries to use them in a
+   * post-update hook.
+   */
+  protected function handler() {
+    if (!$this->handler) {
+      $this->handler = new Handler($this->composer, $this->io);
+      // On instantiation of our handler, notify it if the 'require' command
+      // was executed.
+      if ($this->requireWasCalled) {
+        $this->handler->requireWasCalled();
+      }
+    }
+    return $this->handler;
+  }
+
+}

vendor/drupal/core-composer-scaffold/PostPackageEventListenerInterface.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Installer\PackageEvent;
+
+/**
+ * Interface for post package event listeners.
+ *
+ * @see \Drupal\Composer\Plugin\Scaffold\Handler::onPostPackageEvent
+ *
+ * @internal
+ */
+interface PostPackageEventListenerInterface {
+
+  /**
+   * Handles package events during a 'composer require' operation.
+   *
+   * @param \Composer\Installer\PackageEvent $event
+   *   Composer package event sent on install/update/remove.
+   */
+  public function event(PackageEvent $event);
+
+}

vendor/drupal/core-composer-scaffold/README.md

@@ -0,0 +1,522 @@
+# Drupal Composer Scaffold
+
+This project provides a composer plugin making the Drupal core Composer package
+work correctly in a Composer project.
+
+This takes care of:
+  - Placing scaffold files (like `index.php`, `update.php`, …) from the
+    `drupal/core` project into their desired location inside the web root. Only
+    individual files may be scaffolded with this plugin.
+  - Writing an autoload.php file to the web root, which includes the Composer
+    autoload.php file.
+
+The purpose of scaffolding files is to allow Drupal sites to be fully managed by
+Composer, and still allow individual asset files to be placed in arbitrary
+locations. The goal of doing this is to enable a properly configured composer
+template to produce a file layout that exactly matches the file layout of a
+Drupal 8.7.x and earlier tarball distribution. Other file layouts will also be
+possible; for example, a project layout very similar to the current
+[drupal-composer/drupal-project](https://github.com/drupal-composer/drupal-scaffold)
+template will also be provided. When one of these projects is used, the user
+should be able to use `composer require` and `composer update` on a Drupal site
+immediately after extracting the downloaded archive.
+
+Note that the dependencies of a Drupal site are only able to scaffold files if
+explicitly granted that right in the top-level composer.json file. See
+[allowed packages](#allowed-packages), below.
+
+## Usage
+
+Drupal Composer Scaffold is used by requiring `drupal/core-composer-scaffold` in your
+project, and providing configuration settings in the `extra` section of your
+project's composer.json file. Additional configuration from the composer.json
+file of your project's dependencies is also consulted in order to scaffold the
+files a project needs. Additional information may be added to the beginning or
+end of scaffold files, as is commonly done to `.htaccess` and `robots.txt`
+files. See [altering scaffold files](#altering-scaffold-files) for more
+information.
+
+Typically, the scaffold operations run automatically as needed, e.g. after
+`composer install`, so it is usually not necessary to do anything different
+to scaffold a project once the configuration is set up in the project
+composer.json file, as described below. To scaffold files directly, run:
+```
+composer drupal:scaffold
+```
+
+### Allowed Packages
+
+Scaffold files are stored inside of projects that are required from the main
+project's composer.json file as usual. The scaffolding operation happens after
+`composer install`, and involves copying or symlinking the desired assets to
+their destination location. In order to prevent arbitrary dependencies from
+copying files via the scaffold mechanism, only those projects that are
+specifically permitted by the top-level project will be used to scaffold files.
+
+Example: Permit scaffolding from the project `upstream/project`
+```
+  "name": "my/project",
+  ...
+  "extra": {
+    "drupal-scaffold": {
+      "allowed-packages": [
+        "upstream/project"
+      ],
+      ...
+    }
+  }
+```
+Allowing a package to scaffold files also permits it to delegate permission to
+scaffold to any project that it requires itself. This allows a package to
+organize its scaffold assets as it sees fit. For example, if `upstream/project`
+stores its assets in a subproject `upstream/assets`, `upstream/assets` would
+implicitly be allowed to scaffold files.
+
+It is possible for a project to obtain scaffold files from multiple projects.
+For example, a Drupal project using a distribution, and installing on a specific
+web hosting service provider might take its scaffold files from:
+
+- Drupal core
+- Its distribution
+- A project provided by the hosting provider
+- The project itself
+
+Each project allowed to scaffold by the top-level project will be used in turn,
+with projects declared later in the `allowed-packages` list taking precedence
+over the projects named before. `drupal/core` is implicitly allowed and will be
+placed at the top of the list. The top-level composer.json itself is also
+implicitly allowed to scaffold files, and its scaffold files have highest
+priority.
+
+### Defining Project Locations
+
+The top-level project in turn must define where the web root is located. It does
+so via the `locations` mapping, as shown below:
+```
+  "name": "my/project",
+  ...
+  "extra": {
+    "drupal-scaffold": {
+      "locations": {
+        "web-root": "./docroot"
+      },
+      ...
+    }
+  }
+```
+This makes it possible to configure a project with different file layouts; for
+example, either the `drupal/drupal` file layout or the
+`drupal-composer/drupal-project` file layout could be used to set up a project.
+
+If a web-root is not explicitly defined, then it will default to `.`, the same
+directory as the composer.json file.
+
+### Altering Scaffold Files
+
+Sometimes, a project might wish to use a scaffold file provided by a dependency,
+but alter it in some way. Two forms of alteration are supported: appending and
+patching.
+
+The example below shows a project that appends additional entries onto the end
+of the `robots.txt` file provided by `drupal/core`:
+```
+  "name": "my/project",
+  ...
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/robots.txt": {
+          "append": "assets/my-robots-additions.txt",
+        }
+      }
+    }
+  }
+```
+It is also possible to prepend to a scaffold file instead of, or in addition to
+appending by including a "prepend" entry that provides the relative path to the
+file to prepend to the scaffold file.
+
+The example below demonstrates the use of the `post-drupal-scaffold-cmd` hook
+to patch the `.htaccess` file using a patch.
+```
+  "name": "my/project",
+  ...
+  "scripts": {
+    "post-drupal-scaffold-cmd": [
+      "cd docroot && patch -p1 <../patches/htaccess-ssl.patch"
+    ]
+  }
+```
+
+### Defining Scaffold Files
+
+The placement of scaffold assets is under the control of the project that
+provides them, but the location is always relative to some directory defined by
+the root project -- usually the web root. For example, the scaffold file
+`robots.txt` is copied from its source location, `assets/robots.txt` into the
+web root in the snippet below.
+```
+{
+  "name": "drupal/assets",
+  ...
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/robots.txt": "assets/robots.txt",
+        ...
+      }
+    }
+  }
+}
+```
+
+### Excluding Scaffold Files
+
+Sometimes, a project might prefer to entirely replace a scaffold file provided
+by a dependency, and receive no further updates for it. This can be done by
+setting the value for the scaffold file to exclude to `false`:
+```
+  "name": "my/project",
+  ...
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/robots.txt": false
+      }
+    }
+  }
+```
+If possible, use the `append` and `prepend` directives as explained in [altering
+scaffold files](#altering-scaffold-files), above. Excluding a file means that
+your project will not get any bug fixes or other updates to files that are
+modified locally.
+
+### Overwrite
+
+By default, scaffold files overwrite whatever content exists at the target
+location. Sometimes a project may wish to provide the initial contents for a
+file that will not be changed in subsequent updates. This can be done by setting
+the `overwrite` flag to `false`, as shown in the example below:
+```
+{
+  "name": "service-provider/d8-scaffold-files",
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/sites/default/settings.php": {
+          "mode": "replace",
+          "path": "assets/sites/default/settings.php",
+          "overwrite": false
+        }
+      }
+    }
+  }
+}
+```
+Note that the `overwrite` directive is intended to be used by starter kits,
+service providers, and so on. Individual Drupal sites should exclude the file
+by setting its value to false instead.
+
+### Autoload File
+
+The scaffold tool automatically creates the required `autoload.php` file at the
+Drupal root as part of the scaffolding operation. This file should not be
+modified or customized in any way. If it is committed to the repository, though,
+then the scaffold tool will stop managing it. If the location of the `vendor`
+directory is changed for any reason, and the `autoload.php` file has been
+committed to the repository, manually delete it and then run `composer install`
+to update it.
+
+## Specifications
+
+Reference section for the configuration directives for the "drupal-scaffold"
+section of the "extra" section of a `composer.json` file appear below.
+
+### allowed-packages
+
+The `allowed-packages` configuration setting contains an ordered list of package
+names that will be used during the scaffolding phase.
+```
+"allowed-packages": [
+  "example/assets",
+],
+```
+### file-mapping
+
+The `file-mapping` configuration setting consists of a map from the destination
+path of the file to scaffold to a set of properties that control how the file
+should be scaffolded.
+
+The available properties are as follows:
+
+- mode: One of "replace", "append" or "skip".
+- path: The path to the source file to write over the destination file.
+- prepend: The path to the source file to prepend to the destination file, which
+  must always be a scaffold file provided by some other project.
+- append: Like `prepend`, but appends content rather than prepends.
+- overwrite: If `false`, prevents a `replace` from happening if the destination
+  already exists.
+
+The mode may be inferred from the other properties. If the mode is not
+specified, then the following defaults will be supplied:
+
+- replace: Selected if a `path` property is present, or if the entry's value is
+  a string rather than a property set.
+- append: Selected if a `prepend` or `append` property is present.
+- skip: Selected if the entry's value is a boolean `false`.
+
+Examples:
+```
+"file-mapping": {
+  "[web-root]/sites/default/default.settings.php": {
+    "mode": "replace",
+    "path": "assets/sites/default/default.settings.php",
+    "overwrite": true
+  },
+  "[web-root]/sites/default/settings.php": {
+    "mode": "replace",
+    "path": "assets/sites/default/settings.php",
+    "overwrite": false
+  },
+  "[web-root]/robots.txt": {
+    "mode": "append",
+    "prepend": "assets/robots-prequel.txt",
+    "append": "assets/robots-append.txt"
+  },
+  "[web-root]/.htaccess": {
+    "mode": "skip",
+  }
+}
+```
+The short-form of the above example would be:
+```
+"file-mapping": {
+  "[web-root]/sites/default/default.settings.php": "assets/sites/default/default.settings.php",
+  "[web-root]/sites/default/settings.php": {
+    "path": "assets/sites/default/settings.php",
+    "overwrite": false
+  },
+  "[web-root]/robots.txt": {
+    "prepend": "assets/robots-prequel.txt",
+    "append": "assets/robots-append.txt"
+  },
+  "[web-root]/.htaccess": false
+}
+```
+Note that there is no distinct "prepend" mode; "append" mode is used to both
+append and prepend to scaffold files. The reason for this is that scaffold file
+entries are identified in the file-mapping section keyed by their destination
+path, and it is not possible for multiple entries to have the same key. If
+"prepend" were a separate mode, then it would not be possible to both prepend
+and append to the same file.
+
+By default, append operations may only be applied to files that were scaffolded
+by a previously evaluated project. If the `force-append` attribute is added to
+an `append` operation, though, then the append will be made to non-scaffolded
+files if and only if the append text does not already appear in the file. When
+using this mode, it is also possible to provide default contents to use in the
+event that the destination file is entirely missing.
+
+The example below demonstrates scaffolding a settings-custom.php file, and
+including it from the existing `settings.php` file.
+
+```
+"file-mapping": {
+  "[web-root]/sites/default/settings-custom.php": "assets/settings-custom.php",
+  "[web-root]/sites/default/settings.php": {
+    "append": "assets/include-settings-custom.txt",
+    "force-append": true,
+    "default": "assets/initial-default-settings.txt"
+  }
+}
+```
+
+Note that the example above still works if used with a project that scaffolds
+the settings.php file.
+
+### gitignore
+
+The `gitignore` configuration setting controls whether or not this plugin will
+manage `.gitignore` files for files written during the scaffold operation.
+
+- true: `.gitignore` files will be updated when scaffold files are written.
+- false: `.gitignore` files will never be modified.
+- Not set: `.gitignore` files will be updated if the target directory is a local
+working copy of a git repository, and the `vendor` directory is ignored
+in that repository.
+
+### locations
+
+The `locations` configuration setting contains a list of named locations that
+may be used in placing scaffold files. The only required location is `web-root`.
+Other locations may also be defined if desired.
+```
+"locations": {
+  "web-root": "./docroot"
+},
+```
+### symlink
+
+The `symlink` property causes `replace` operations to make a symlink to the
+source file rather than copying it. This is useful when doing core development,
+as the symlink files themselves should not be edited. Note that `append`
+operations override the `symlink` option, to prevent the original scaffold
+assets from being altered.
+```
+"symlink": true,
+```
+## Managing Scaffold Files
+
+Scaffold files should be treated the same way that the `vendor` directory is
+handled. If you need to commit `vendor` (e.g. in order to deploy your site),
+then you should also commit your scaffold files. You should not commit your
+`vendor` directory or scaffold files unless it is necessary.
+
+If a dependency provides a scaffold file with `overwrite` set to `false`, that
+file should be committed to your repository.
+
+By default, `.gitignore` files will be automatically updated if needed when
+scaffold files are written. See the `gitignore` setting in the Specifications
+section above.
+
+## Examples
+
+Some full-length examples appear below.
+
+Sample composer.json for a project that relies on packages that use composer-scaffold:
+```
+{
+  "name": "my/project",
+  "require": {
+    "drupal/core-composer-scaffold": "*",
+    "composer/installers": "^2.3",
+    "cweagans/composer-patches": "^1.6.5",
+    "drupal/core": "^8.8.x-dev",
+    "service-provider/d8-scaffold-files": "^1"
+  },
+  "config": {
+    "optimize-autoloader": true,
+    "sort-packages": true
+  },
+  "extra": {
+    "drupal-scaffold": {
+      "locations": {
+        "web-root": "./docroot"
+      },
+      "symlink": true,
+      "file-mapping": {
+        "[web-root]/.htaccess": false,
+        "[web-root]/robots.txt": "assets/robots-default.txt"
+      }
+    }
+  }
+}
+```
+
+Sample composer.json for drupal/core, with assets placed in a different project:
+
+```
+{
+  "name": "drupal/core",
+  "extra": {
+    "drupal-scaffold": {
+      "allowed-packages": [
+        "drupal/assets",
+      ]
+    }
+  }
+}
+```
+
+Sample composer.json for composer-scaffold files in drupal/assets:
+
+```
+{
+  "name": "drupal/assets",
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/.csslintrc": "assets/.csslintrc",
+        "[web-root]/.editorconfig": "assets/.editorconfig",
+        "[web-root]/.eslintignore": "assets/.eslintignore",
+        "[web-root]/.eslintrc.json": "assets/.eslintrc.json",
+        "[web-root]/.gitattributes": "assets/.gitattributes",
+        "[web-root]/.ht.router.php": "assets/.ht.router.php",
+        "[web-root]/.htaccess": "assets/.htaccess",
+        "[web-root]/sites/default/default.services.yml": "assets/default.services.yml",
+        "[web-root]/sites/default/default.settings.php": "assets/default.settings.php",
+        "[web-root]/sites/example.settings.local.php": "assets/example.settings.local.php",
+        "[web-root]/sites/example.sites.php": "assets/example.sites.php",
+        "[web-root]/index.php": "assets/index.php",
+        "[web-root]/robots.txt": "assets/robots.txt",
+        "[web-root]/update.php": "assets/update.php",
+      }
+    }
+  }
+}
+```
+
+Sample composer.json for a library that implements composer-scaffold:
+
+```
+{
+  "name": "service-provider/d8-scaffold-files",
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/sites/default/settings.php": "assets/sites/default/settings.php"
+      }
+    }
+  }
+}
+```
+
+Append to robots.txt:
+
+```
+{
+  "name": "service-provider/d8-scaffold-files",
+  "extra": {
+    "drupal-scaffold": {
+      "file-mapping": {
+        "[web-root]/robots.txt": {
+          "append": "assets/my-robots-additions.txt",
+        }
+      }
+    }
+  }
+}
+```
+
+Patch a file after it's copied:
+
+```
+"post-drupal-scaffold-cmd": [
+  "cd docroot && patch -p1 <../patches/htaccess-ssl.patch"
+]
+```
+
+## Related Plugins
+
+### drupal-composer/drupal-scaffold
+
+Previous versions of Drupal Composer Scaffold (see community project,
+[drupal-composer/drupal-scaffold](https://github.com/drupal-composer/drupal-project))
+downloaded each scaffold file directly from its distribution server (e.g.
+`https://git.drupalcode.org`) to the desired destination directory. This was
+necessary, because there was no subtree split of the scaffold files available.
+Copying the scaffold assets from projects already downloaded by Composer is more
+effective, as downloading and unpacking archive files is more efficient than
+downloading each scaffold file individually.
+
+### composer/installers
+
+The [composer/installers](https://github.com/composer/installers) plugin is
+similar to this plugin in that it allows dependencies to be installed in
+locations other than the `vendor` directory. However, Composer and the
+`composer/installers` plugin have a limitation that one project cannot be moved
+inside of another project. Therefore, if you use `composer/installers` to place
+Drupal modules inside the directory `web/modules/contrib`, then you cannot also
+use `composer/installers` to place files such as `index.php` and `robots.txt`
+into the `web` directory. The drupal-scaffold plugin was created to work around
+this limitation.

vendor/drupal/core-composer-scaffold/ScaffoldFileInfo.php

@@ -0,0 +1,140 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\IO\IOInterface;
+use Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface;
+
+/**
+ * Data object that keeps track of one scaffold file.
+ *
+ * Scaffold files are identified primarily by their destination path. Each
+ * scaffold file also has an 'operation' object that controls how the scaffold
+ * file will be placed (e.g. via copy or symlink, or maybe by appending multiple
+ * files together). The operation may have one or more source files.
+ *
+ * @internal
+ */
+class ScaffoldFileInfo {
+
+  /**
+   * The path to the destination.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   */
+  protected $destination;
+
+  /**
+   * The operation used to create the destination.
+   *
+   * @var \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface
+   */
+  protected $op;
+
+  /**
+   * Constructs a ScaffoldFileInfo object.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath $destination
+   *   The full and relative paths to the destination file and the package
+   *   defining it.
+   * @param \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface $op
+   *   Operations object that will handle scaffolding operations.
+   */
+  public function __construct(ScaffoldFilePath $destination, OperationInterface $op) {
+    $this->destination = $destination;
+    $this->op = $op;
+  }
+
+  /**
+   * Gets the Scaffold operation.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\OperationInterface
+   *   Operations object that handles scaffolding (copy, make symlink, etc).
+   */
+  public function op() {
+    return $this->op;
+  }
+
+  /**
+   * Gets the package name.
+   *
+   * @return string
+   *   The name of the package this scaffold file info was collected from.
+   */
+  public function packageName() {
+    return $this->destination->packageName();
+  }
+
+  /**
+   * Gets the destination.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\ScaffoldFilePath
+   *   The scaffold path to the destination file.
+   */
+  public function destination() {
+    return $this->destination;
+  }
+
+  /**
+   * Determines if this scaffold file has been overridden by another package.
+   *
+   * @param string $providing_package
+   *   The name of the package that provides the scaffold file at this location,
+   *   as returned by self::findProvidingPackage()
+   *
+   * @return bool
+   *   Whether this scaffold file if overridden or removed.
+   */
+  public function overridden($providing_package) {
+    return $this->packageName() !== $providing_package;
+  }
+
+  /**
+   * Replaces placeholders in a message.
+   *
+   * @param string $message
+   *   Message with placeholders to fill in.
+   * @param array $extra
+   *   Additional data to merge with the interpolator.
+   * @param mixed $default
+   *   Default value to use for missing placeholders, or FALSE to keep them.
+   *
+   * @return string
+   *   Interpolated string with placeholders replaced.
+   */
+  public function interpolate($message, array $extra = [], $default = FALSE) {
+    $interpolator = $this->destination->getInterpolator();
+    return $interpolator->interpolate($message, $extra, $default);
+  }
+
+  /**
+   * Moves a single scaffold file from source to destination.
+   *
+   * @param \Composer\IO\IOInterface $io
+   *   The scaffold file to be processed.
+   * @param \Drupal\Composer\Plugin\Scaffold\ScaffoldOptions $options
+   *   Assorted operational options, e.g. whether the destination should be a
+   *   symlink.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Operations\ScaffoldResult
+   *   The scaffold result.
+   */
+  public function process(IOInterface $io, ScaffoldOptions $options) {
+    return $this->op()->process($this->destination, $io, $options);
+  }
+
+  /**
+   * Returns TRUE if the target does not exist or has changed.
+   *
+   * @return bool
+   *   TRUE if the target does not exist or has changed, FALSE otherwise.
+   */
+  final public function hasChanged() {
+    $path = $this->destination()->fullPath();
+    if (!file_exists($path)) {
+      return TRUE;
+    }
+    return $this->op()->contents() !== file_get_contents($path);
+  }
+
+}

vendor/drupal/core-composer-scaffold/ScaffoldFilePath.php

@@ -0,0 +1,202 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+use Composer\Util\Filesystem;
+
+/**
+ * Manage the path to a file to scaffold.
+ *
+ * Both the relative and full path to the file is maintained so that the shorter
+ * name may be used in progress and error messages, as needed. The name of the
+ * package that provided the file path is also recorded for the same reason.
+ *
+ * ScaffoldFilePaths may be used to represent destination scaffold files, or the
+ * source files used to create them. Static factory methods named
+ * destinationPath and sourcePath, respectively, are provided to create
+ * ScaffoldFilePath objects.
+ *
+ * @internal
+ */
+class ScaffoldFilePath {
+
+  /**
+   * The type of scaffold file this is,'autoload', 'dest' or 'src'.
+   *
+   * @var string
+   */
+  protected $type;
+
+  /**
+   * The name of the package containing the file.
+   *
+   * @var string
+   */
+  protected $packageName;
+
+  /**
+   * The relative path to the file.
+   *
+   * @var string
+   */
+  protected $relativePath;
+
+  /**
+   * The full path to the file.
+   *
+   * @var string
+   */
+  protected $fullPath;
+
+  /**
+   * ScaffoldFilePath constructor.
+   *
+   * @param string $path_type
+   *   The type of scaffold file this is,'autoload', 'dest' or 'src'.
+   * @param string $package_name
+   *   The name of the package containing the file.
+   * @param string $rel_path
+   *   The relative path to the file.
+   * @param string $full_path
+   *   The full path to the file.
+   */
+  public function __construct($path_type, $package_name, $rel_path, $full_path) {
+    $this->type = $path_type;
+    $this->packageName = $package_name;
+    $this->relativePath = $rel_path;
+    $this->fullPath = $full_path;
+
+    // Ensure that the full path really is a full path. We do not use
+    // 'realpath' here because the file specified by the full path might
+    // not exist yet.
+    $fs = new Filesystem();
+    if (!$fs->isAbsolutePath($this->fullPath)) {
+      $this->fullPath = getcwd() . '/' . $this->fullPath;
+    }
+  }
+
+  /**
+   * Gets the name of the package this source file was pulled from.
+   *
+   * @return string
+   *   Name of package.
+   */
+  public function packageName() {
+    return $this->packageName;
+  }
+
+  /**
+   * Gets the relative path to the source file (best to use in messages).
+   *
+   * @return string
+   *   Relative path to file.
+   */
+  public function relativePath() {
+    return $this->relativePath;
+  }
+
+  /**
+   * Gets the full path to the source file.
+   *
+   * @return string
+   *   Full path to file.
+   */
+  public function fullPath() {
+    return $this->fullPath;
+  }
+
+  /**
+   * Converts the relative source path into an absolute path.
+   *
+   * The path returned will be relative to the package installation location.
+   *
+   * @param string $package_name
+   *   The name of the package containing the source file. Only used for error
+   *   messages.
+   * @param string $package_path
+   *   The installation path of the package containing the source file.
+   * @param string $destination
+   *   Destination location provided as a relative path. Only used for error
+   *   messages.
+   * @param string $source
+   *   Source location provided as a relative path.
+   *
+   * @return self
+   *   Object wrapping the relative and absolute path to the source file.
+   */
+  public static function sourcePath($package_name, $package_path, $destination, $source) {
+    // Complain if there is no source path.
+    if (empty($source)) {
+      throw new \RuntimeException("No scaffold file path given for {$destination} in package {$package_name}.");
+    }
+    // Calculate the full path to the source scaffold file.
+    $source_full_path = $package_path . '/' . $source;
+    if (!file_exists($source_full_path)) {
+      throw new \RuntimeException("Scaffold file {$source} not found in package {$package_name}.");
+    }
+    if (is_dir($source_full_path)) {
+      throw new \RuntimeException("Scaffold file {$source} in package {$package_name} is a directory; only files may be scaffolded.");
+    }
+    return new self('src', $package_name, $source, $source_full_path);
+  }
+
+  /**
+   * Converts the relative destination path into an absolute path.
+   *
+   * Any placeholders in the destination path, e.g. '[web-root]', will be
+   * replaced using the provided location replacements interpolator.
+   *
+   * @param string $package_name
+   *   The name of the package defining the destination path.
+   * @param string $destination
+   *   The relative path to the destination file being scaffolded.
+   * @param \Drupal\Composer\Plugin\Scaffold\Interpolator $location_replacements
+   *   Interpolator that includes the [web-root] and any other available
+   *   placeholder replacements.
+   *
+   * @return self
+   *   Object wrapping the relative and absolute path to the destination file.
+   */
+  public static function destinationPath($package_name, $destination, Interpolator $location_replacements) {
+    $dest_full_path = $location_replacements->interpolate($destination);
+    return new self('dest', $package_name, $destination, $dest_full_path);
+  }
+
+  /**
+   * Adds data about the relative and full path to the provided interpolator.
+   *
+   * @param \Drupal\Composer\Plugin\Scaffold\Interpolator $interpolator
+   *   Interpolator to add data to.
+   * @param string $name_prefix
+   *   (optional) Prefix to add before -rel-path and -full-path item names.
+   *   Defaults to path type provided when constructing this object.
+   */
+  public function addInterpolationData(Interpolator $interpolator, $name_prefix = '') {
+    if (empty($name_prefix)) {
+      $name_prefix = $this->type;
+    }
+    $data = [
+      'package-name' => $this->packageName(),
+      "{$name_prefix}-rel-path" => $this->relativePath(),
+      "{$name_prefix}-full-path" => $this->fullPath(),
+    ];
+    $interpolator->addData($data);
+  }
+
+  /**
+   * Interpolate a string using the data from this scaffold file info.
+   *
+   * @param string $name_prefix
+   *   (optional) Prefix to add before -rel-path and -full-path item names.
+   *   Defaults to path type provided when constructing this object.
+   *
+   * @return \Drupal\Composer\Plugin\Scaffold\Interpolator
+   *   An interpolator for making string replacements.
+   */
+  public function getInterpolator($name_prefix = '') {
+    $interpolator = new Interpolator();
+    $this->addInterpolationData($interpolator, $name_prefix);
+    return $interpolator;
+  }
+
+}

vendor/drupal/core-composer-scaffold/ScaffoldOptions.php

@@ -0,0 +1,203 @@
+<?php
+
+namespace Drupal\Composer\Plugin\Scaffold;
+
+/**
+ * Per-project options from the 'extras' section of the composer.json file.
+ *
+ * Projects that describe scaffold files do so via their scaffold options. This
+ * data is pulled from the 'drupal-scaffold' portion of the extras section of
+ * the project data.
+ *
+ * @internal
+ */
+class ScaffoldOptions {
+
+  /**
+   * The raw data from the 'extras' section of the top-level composer.json file.
+   *
+   * @var array
+   */
+  protected $options = [];
+
+  /**
+   * ScaffoldOptions constructor.
+   *
+   * @param array $options
+   *   The scaffold options taken from the 'drupal-scaffold' section.
+   */
+  protected function __construct(array $options) {
+    $this->options = $options + [
+      "allowed-packages" => [],
+      "locations" => [],
+      "symlink" => FALSE,
+      "file-mapping" => [],
+    ];
+
+    // Define any default locations.
+    $this->options['locations'] += [
+      'project-root' => '.',
+      'web-root' => '.',
+    ];
+  }
+
+  /**
+   * Determines if the provided 'extras' section has scaffold options.
+   *
+   * @param array $extras
+   *   The contents of the 'extras' section.
+   *
+   * @return bool
+   *   True if scaffold options have been declared
+   */
+  public static function hasOptions(array $extras) {
+    return array_key_exists('drupal-scaffold', $extras);
+  }
+
+  /**
+   * Creates a scaffold options object.
+   *
+   * @param array $extras
+   *   The contents of the 'extras' section.
+   *
+   * @return self
+   *   The scaffold options object representing the provided scaffold options
+   */
+  public static function create(array $extras) {
+    $options = static::hasOptions($extras) ? $extras['drupal-scaffold'] : [];
+    return new self($options);
+  }
+
+  /**
+   * Creates a new scaffold options object with some values overridden.
+   *
+   * @param array $options
+   *   Override values.
+   *
+   * @return self
+   *   The scaffold options object representing the provided scaffold options
+   */
+  protected function override(array $options) {
+    return new self($options + $this->options);
+  }
+
+  /**
+   * Creates a new scaffold options object with an overridden 'symlink' value.
+   *
+   * @param bool $symlink
+   *   Whether symlinking should be enabled or not.
+   *
+   * @return self
+   *   The scaffold options object representing the provided scaffold options
+   */
+  public function overrideSymlink($symlink) {
+    return $this->override(['symlink' => $symlink]);
+  }
+
+  /**
+   * Determines whether any allowed packages were defined.
+   *
+   * @return bool
+   *   Whether there are allowed packages
+   */
+  public function hasAllowedPackages() {
+    return !empty($this->allowedPackages());
+  }
+
+  /**
+   * Gets allowed packages from these options.
+   *
+   * @return array
+   *   The list of allowed packages
+   */
+  public function allowedPackages() {
+    return $this->options['allowed-packages'];
+  }
+
+  /**
+   * Gets the location mapping table, e.g. 'webroot' => './'.
+   *
+   * @return array
+   *   A map of name : location values
+   */
+  public function locations() {
+    return $this->options['locations'];
+  }
+
+  /**
+   * Determines whether a given named location is defined.
+   *
+   * @param string $name
+   *   The location name to search for.
+   *
+   * @return bool
+   *   True if the specified named location exist.
+   */
+  protected function hasLocation($name) {
+    return array_key_exists($name, $this->locations());
+  }
+
+  /**
+   * Gets a specific named location.
+   *
+   * @param string $name
+   *   The name of the location to fetch.
+   *
+   * @return string
+   *   The value of the provided named location
+   */
+  public function getLocation($name) {
+    return $this->hasLocation($name) ? $this->locations()[$name] : FALSE;
+  }
+
+  /**
+   * Determines if symlink mode is set.
+   *
+   * @return bool
+   *   Whether or not 'symlink' mode
+   */
+  public function symlink() {
+    return $this->options['symlink'];
+  }
+
+  /**
+   * Determines if there are file mappings.
+   *
+   * @return bool
+   *   Whether or not the scaffold options contain any file mappings
+   */
+  public function hasFileMapping() {
+    return !empty($this->fileMapping());
+  }
+
+  /**
+   * Returns the actual file mappings.
+   *
+   * @return array
+   *   File mappings for just this config type.
+   */
+  public function fileMapping() {
+    return $this->options['file-mapping'];
+  }
+
+  /**
+   * Determines if there is defined a value for the 'gitignore' option.
+   *
+   * @return bool
+   *   Whether or not there is a 'gitignore' option setting
+   */
+  public function hasGitIgnore() {
+    return isset($this->options['gitignore']);
+  }
+
+  /**
+   * Gets the value of the 'gitignore' option.
+   *
+   * @return bool
+   *   The 'gitignore' option, or TRUE if undefined.
+   */
+  public function gitIgnore() {
+    return $this->hasGitIgnore() ? $this->options['gitignore'] : TRUE;
+  }
+
+}

vendor/drupal/core-composer-scaffold/TESTING.txt

@@ -0,0 +1,18 @@
+HOW-TO: Test this Drupal composer plugin
+
+In order to test this plugin, you'll need to get the entire Drupal repo and
+run the tests there.
+
+You'll find the tests under core/tests/Drupal/Tests/Composer/Plugin.
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can find more information about running PHPUnit tests with Drupal here:
+https://www.drupal.org/node/2116263
+
+Each component in the Drupal\Composer\Plugin namespace has its own annotated test
+group. You can use this group to run only the tests for this component. Like
+this:
+
+$ ./vendor/bin/phpunit -c core --group Scaffold

vendor/drupal/core-composer-scaffold/composer.json

@@ -0,0 +1,32 @@
+{
+  "name": "drupal/core-composer-scaffold",
+  "description": "A flexible Composer project scaffold builder.",
+  "type": "composer-plugin",
+  "keywords": ["drupal"],
+  "homepage": "https://www.drupal.org/project/drupal",
+  "license": "GPL-2.0-or-later",
+  "require": {
+    "composer-plugin-api": "^2",
+    "php": ">=7.3.0"
+  },
+  "conflict": {
+    "drupal-composer/drupal-scaffold": "*"
+  },
+  "autoload": {
+    "psr-4": {
+      "Drupal\\Composer\\Plugin\\Scaffold\\": ""
+    }
+  },
+  "extra": {
+    "class": "Drupal\\Composer\\Plugin\\Scaffold\\Plugin",
+    "branch-alias": {
+      "dev-master": "1.0.x-dev"
+    }
+  },
+  "config": {
+    "sort-packages": true
+  },
+  "require-dev": {
+    "composer/composer": "^1.8@stable"
+  }
+}

vendor/drupal/core-project-message/LICENSE.txt

@@ -0,0 +1,339 @@
+        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
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+
+  When we speak of free software, we are referring to freedom, not
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+
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+
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+
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+
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+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
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+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.

vendor/drupal/core-project-message/Message.php

@@ -0,0 +1,117 @@
+<?php
+
+namespace Drupal\Composer\Plugin\ProjectMessage;
+
+use Composer\Package\RootPackageInterface;
+
+/**
+ * Determine configuration.
+ *
+ * @internal
+ */
+class Message {
+
+  /**
+   * The root package.
+   *
+   * @var \Composer\Package\RootPackageInterface
+   */
+  protected $rootPackage;
+
+  /**
+   * The name of the event.
+   *
+   * @var string
+   */
+  protected $eventName;
+
+  /**
+   * The message to display.
+   *
+   * @var string[]
+   */
+  protected $messageText = [];
+
+  /**
+   * Construct a Config object.
+   *
+   * @param \Composer\Package\RootPackageInterface $root_package
+   *   Composer package object for the root package.
+   * @param string $event_name
+   *   The event name.
+   */
+  public function __construct(RootPackageInterface $root_package, $event_name) {
+    $this->rootPackage = $root_package;
+    $this->eventName = $event_name;
+  }
+
+  public function getText() {
+    if ($this->messageText) {
+      return $this->messageText;
+    }
+    $package_config = $this->rootPackage->getExtra();
+    $file = $this->eventName . '-message.txt';
+    if ($config_file = $package_config['drupal-core-project-message'][$this->eventName . '-file'] ?? FALSE) {
+      $file = $config_file;
+    }
+
+    $message = $package_config['drupal-core-project-message'][$this->eventName . '-message'] ?? [];
+
+    if ($message) {
+      $this->messageText = $message;
+    }
+    else {
+      $this->messageText = $this->getMessageFromFile($file);
+    }
+
+    // Include structured support info from composer.json.
+    if ($config_keys = $package_config['drupal-core-project-message']['include-keys'] ?? FALSE) {
+      foreach ($config_keys as $config_key) {
+        switch ($config_key) {
+          case 'name':
+            if ($homepage = $this->rootPackage->getName()) {
+              $this->messageText[] = '  * Name: ' . $homepage;
+            }
+            break;
+
+          case 'description':
+            if ($homepage = $this->rootPackage->getDescription()) {
+              $this->messageText[] = '  * Description: ' . $homepage;
+            }
+            break;
+
+          case 'homepage':
+            if ($homepage = $this->rootPackage->getHomepage()) {
+              $this->messageText[] = '  * Homepage: ' . $homepage;
+            }
+            break;
+
+          case 'support':
+            if ($support = $this->rootPackage->getSupport()) {
+              $this->messageText[] = '  * Support:';
+              foreach ($support as $support_key => $support_value) {
+                $this->messageText[] = '    * ' . $support_key . ': ' . $support_value;
+              }
+            }
+            break;
+        }
+      }
+    }
+
+    return $this->messageText;
+  }
+
+  /**
+   * Reads the message file as an array.
+   *
+   * @param string $file
+   *   The file to read. Relative paths are relative to the project directory.
+   *
+   * @return string[]
+   *   The message text.
+   */
+  protected function getMessageFromFile($file) {
+    return file_exists($file) ? file($file, FILE_IGNORE_NEW_LINES) : [];
+  }
+
+}

vendor/drupal/core-project-message/MessagePlugin.php

@@ -0,0 +1,77 @@
+<?php
+
+namespace Drupal\Composer\Plugin\ProjectMessage;
+
+use Composer\Composer;
+use Composer\EventDispatcher\EventSubscriberInterface;
+use Composer\IO\IOInterface;
+use Composer\Plugin\PluginInterface;
+use Composer\Script\Event;
+use Composer\Script\ScriptEvents;
+
+/**
+ * A Composer plugin to display a message after creating a project.
+ *
+ * @internal
+ */
+class MessagePlugin implements PluginInterface, EventSubscriberInterface {
+
+  /**
+   * Composer object.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * IO object.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * Configuration.
+   *
+   * @var \Drupal\Composer\Plugin\VendorHardening\Config
+   */
+  protected $config;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function activate(Composer $composer, IOInterface $io) {
+    $this->composer = $composer;
+    $this->io = $io;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deactivate(Composer $composer, IOInterface $io) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function uninstall(Composer $composer, IOInterface $io) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      ScriptEvents::POST_CREATE_PROJECT_CMD => 'displayPostCreateMessage',
+      ScriptEvents::POST_INSTALL_CMD => 'displayPostCreateMessage',
+    ];
+  }
+
+  public function displayPostCreateMessage(Event $event) {
+    $message = new Message($this->composer->getPackage(), $event->getName());
+    if ($message = $message->getText()) {
+      $this->io->write($message);
+    }
+  }
+
+}

vendor/drupal/core-project-message/README.md

@@ -0,0 +1,101 @@
+The Drupal Project Message Plugin
+=================================
+
+Thanks for using this Drupal component.
+
+You can participate in its development on Drupal.org, through our issue system:
+https://www.drupal.org/project/issues/drupal
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can browse the full Drupal repo here:
+https://git.drupalcode.org/project/drupal
+
+What does it do?
+----------------
+
+This Composer plugin displays a configurable message after Composer installation
+processes have finished.
+
+This is ideal for a 'next steps' type prompt to help get the user oriented.
+
+Currently only two Composer events are supported:
+- post-create-project-cmd, when a `composer create-project` command has
+  finished.
+- post-install-cmd, when a `composer install` command has finished.
+
+How do I set it up?
+-------------------
+
+Require this Composer plugin in your project template composer.json file:
+
+    "require": {
+      "drupal/core-project-message": "^8.8"
+    }
+
+### Configuration
+
+There are three ways to configure this plugin to output information:
+- Using a text file.
+- Using composer.json schema keys.
+- Embedding the information in the extra section of the composer.json file.
+
+### Using a text file
+
+By default, the plugin will respond to `post-install-cmd` or
+`post-create-project-cmd` Composer events by looking for a similarly-named file
+in the root of the project. For instance, if the user issues a `composer
+create-project` command, when that command is finished, the plugin will look for
+a file named `post-create-project-cmd-message.txt` and then display it on the
+command line.
+
+The file should be plain text, with markup suitable for Symfony's
+`OutputInterface::writeln()` method. See documentation here:
+https://symfony.com/doc/3.4/console/coloring.html
+
+You can also configure your own file(s), using the `extra` section of your
+composer.json file:
+
+    "extra": {
+      "drupal-core-project-message": {
+        "post-create-project-cmd-file": "bespoke/special_file.txt"
+      }
+    }
+
+### Using composer.json schema keys
+
+You can tell the plugin to output the structured support information from the
+composer.json file by telling it the keys you wish to display.
+
+Currently, only `name`, `description`, `homepage` and `support` are supported.
+
+    "extra": {
+        "drupal-core-project-message": {
+            "include-keys": ["homepage", "support"],
+        }
+    }
+
+Then you can include this information in your composer.json file, which you
+should probably be doing anyway.
+
+### Embedding the information in the extra section
+
+You can specify text directly within the `extra` section by using the
+`[event-name]-message` key. This message should be an array, with one string for
+each line:
+
+    "extra": {
+      "drupal-core-project-message": {
+        "post-create-project-cmd-message": [
+          "Thanks for installing this project.",
+          "Read our documentation here: http://example.com/docs"
+        ]
+      }
+    }
+
+These strings should be plain text, with markup suitable for Symfony's
+`OutputInterface::writeln()` method. See documentation here:
+https://symfony.com/doc/3.4/console/coloring.html
+
+The `-message` section will always override `-file` for a given event.

vendor/drupal/core-project-message/TESTING.txt

@@ -0,0 +1,18 @@
+HOW-TO: Test this Drupal component
+
+In order to test this component, you'll need to get the entire Drupal repo and
+run the tests there.
+
+You'll find the tests under core/tests/Drupal/Tests/Plugin.
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can find more information about running PHPUnit tests with Drupal here:
+https://www.drupal.org/node/2116263
+
+Each component in the Drupal\Composer namespace has its own annotated test
+group. You can use this group to run only the tests for this component. Like
+this:
+
+$ ./vendor/bin/phpunit -c core --group ProjectMessage

vendor/drupal/core-project-message/composer.json

@@ -0,0 +1,20 @@
+{
+  "name": "drupal/core-project-message",
+  "description": "Adds a message after Composer installation.",
+  "keywords": ["drupal"],
+  "homepage": "https://www.drupal.org/project/drupal",
+  "license": "GPL-2.0-or-later",
+  "type": "composer-plugin",
+  "autoload": {
+    "psr-4": {
+      "Drupal\\Composer\\Plugin\\ProjectMessage\\": "."
+    }
+  },
+  "extra": {
+    "class": "Drupal\\Composer\\Plugin\\ProjectMessage\\MessagePlugin"
+  },
+  "require": {
+    "php": ">=7.3.0",
+    "composer-plugin-api": "^2"
+  }
+}

vendor/drupal/core-recipe-unpack/CommandProvider.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Plugin\Capability\CommandProvider as CommandProviderCapability;
+
+/**
+ * List of all commands provided by this package.
+ *
+ * @internal
+ */
+final class CommandProvider implements CommandProviderCapability {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCommands(): array {
+    return [new UnpackCommand()];
+  }
+
+}

vendor/drupal/core-recipe-unpack/Plugin.php

@@ -0,0 +1,170 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Command\RequireCommand;
+use Composer\Composer;
+use Composer\EventDispatcher\EventSubscriberInterface;
+use Composer\Installer;
+use Composer\IO\IOInterface;
+use Composer\Package\PackageInterface;
+use Composer\Plugin\Capability\CommandProvider;
+use Composer\Plugin\Capable;
+use Composer\Plugin\PluginInterface;
+use Composer\Script\Event;
+use Composer\Script\ScriptEvents;
+use Drupal\Composer\Plugin\RecipeUnpack\CommandProvider as UnpackCommandProvider;
+
+/**
+ * Composer plugin for handling dependency unpacking.
+ *
+ * @internal
+ */
+final class Plugin implements PluginInterface, EventSubscriberInterface, Capable {
+
+  /**
+   * The composer package type of Drupal recipes.
+   */
+  public const string RECIPE_PACKAGE_TYPE = 'drupal-recipe';
+
+  /**
+   * The handler for dependency unpacking.
+   */
+  private UnpackManager $manager;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCapabilities(): array {
+    return [CommandProvider::class => UnpackCommandProvider::class];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function activate(Composer $composer, IOInterface $io): void {
+    $this->manager = new UnpackManager($composer, $io);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function deactivate(Composer $composer, IOInterface $io): void {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function uninstall(Composer $composer, IOInterface $io): void {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    return [
+      ScriptEvents::POST_UPDATE_CMD => 'unpackOnRequire',
+      ScriptEvents::POST_CREATE_PROJECT_CMD => 'unpackOnCreateProject',
+    ];
+  }
+
+  /**
+   * Post update command event callback.
+   */
+  public function unpackOnRequire(Event $event): void {
+    if (!$this->manager->unpackOptions->options['on-require']) {
+      return;
+    }
+
+    // @todo https://www.drupal.org/project/drupal/issues/3523269 Use Composer
+    //   API once it exists.
+    $backtrace = debug_backtrace();
+    $composer = $event->getComposer();
+    foreach ($backtrace as $trace) {
+      if (isset($trace['object']) && $trace['object'] instanceof Installer) {
+        $installer = $trace['object'];
+
+        // Get the list of packages being required. This code is largely copied
+        // from https://github.com/symfony/flex/blob/2.x/src/Flex.php#L218.
+        $updateAllowList = \Closure::bind(function () {
+          return $this->updateAllowList ?? [];
+        }, $installer, $installer)();
+
+        // Determine if the --no-install flag has been passed to require.
+        $isInstalling = \Closure::bind(function () {
+          return $this->install;
+        }, $installer, $installer)();
+      }
+
+      // If the command is a require command, populate the list of recipes to
+      // unpack.
+      if (isset($trace['object']) && $trace['object'] instanceof RequireCommand && isset($installer, $updateAllowList, $isInstalling)) {
+        // Determines if a message has been sent about require-dev and recipes.
+        $devRecipeWarningEmitted = FALSE;
+        $unpackCollection = new UnpackCollection();
+
+        foreach ($updateAllowList as $package_name) {
+          $packages = $composer->getRepositoryManager()->getLocalRepository()->findPackages($package_name);
+          $package = reset($packages);
+
+          if (!$package instanceof PackageInterface) {
+            if (!$isInstalling) {
+              $event->getIO()->write('Recipes are not unpacked when the --no-install option is used.', verbosity: IOInterface::VERBOSE);
+              return;
+            }
+            $event->getIO()->error(sprintf('%s does not resolve to a package.', $package_name));
+            return;
+          }
+
+          // Only recipes are supported.
+          if ($package->getType() === self::RECIPE_PACKAGE_TYPE) {
+            if ($this->manager->unpackOptions->isIgnored($package)) {
+              $event->getIO()->write(sprintf('<info>%s</info> not unpacked because it is ignored.', $package_name), verbosity: IOInterface::VERBOSE);
+            }
+            elseif (UnpackManager::isDevRequirement($package)) {
+              if (!$devRecipeWarningEmitted) {
+                $event->getIO()->write('<info>Recipes required as a development dependency are not automatically unpacked.</info>');
+                $devRecipeWarningEmitted = TRUE;
+              }
+            }
+            else {
+              $unpackCollection->add($package);
+            }
+          }
+        }
+
+        // Unpack any recipes that have been added to the collection.
+        $this->manager->unpack($unpackCollection);
+        // The trace has been processed far enough and the $updateAllowList has
+        // been used.
+        break;
+      }
+    }
+  }
+
+  /**
+   * Post create-project command event callback.
+   */
+  public function unpackOnCreateProject(Event $event): void {
+    $composer = $event->getComposer();
+    $unpackCollection = new UnpackCollection();
+    foreach ($composer->getRepositoryManager()->getLocalRepository()->getPackages() as $package) {
+      // Only recipes are supported.
+      if ($package->getType() === self::RECIPE_PACKAGE_TYPE) {
+        if ($this->manager->unpackOptions->isIgnored($package)) {
+          $event->getIO()->write(sprintf('<info>%s</info> not unpacked because it is ignored.', $package->getName()), verbosity: IOInterface::VERBOSE);
+        }
+        elseif (UnpackManager::isDevRequirement($package)) {
+          continue;
+        }
+        else {
+          $unpackCollection->add($package);
+        }
+      }
+    }
+
+    // Unpack any recipes that have been registered.
+    $this->manager->unpack($unpackCollection);
+  }
+
+}

vendor/drupal/core-recipe-unpack/README.md

@@ -0,0 +1,256 @@
+# Drupal Recipe Unpack Plugin
+
+Thanks for using this Drupal component.
+
+You can participate in its development on Drupal.org, through our issue system:
+https://www.drupal.org/project/issues/drupal
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can browse the full Drupal repo here:
+https://git.drupalcode.org/project/drupal
+
+## Overview
+
+The Recipe Unpacking system is a Composer plugin that manages "drupal-recipe"
+packages. Recipes are special Composer packages designed to bootstrap Drupal
+projects with necessary dependencies. When a recipe is installed, this plugin
+"unpacks" it by moving the recipe's dependencies directly into your project's
+root `composer.json`, and removes the recipe as a project dependency.
+
+## Key Concepts
+
+### What is a Recipe?
+
+A recipe is a Composer package with type `drupal-recipe` that contains a curated
+set of dependencies, configuration and content but no code of its own. Recipes
+are meant to be "unpacked" and "applied" rather than remain as runtime
+dependencies.
+
+### What is Unpacking?
+
+Unpacking is the process where:
+
+1. A recipe's dependencies are added to your project's root `composer.json`
+2. The recipe itself is removed from your dependencies
+3. The `composer.lock` and vendor installation files are updated accordingly
+4. The recipe will remain in the project's recipes folder so it can be applied
+
+## Commands
+
+### `drupal:recipe-unpack`
+
+Unpack a recipe package that's already required in your project.
+
+```bash
+composer drupal:recipe-unpack drupal/example_recipe
+```
+
+Unpack all recipes that are required in your project.
+
+```bash
+composer drupal:recipe-unpack
+```
+
+#### Options
+
+This command doesn't take additional options.
+
+## Automatic Unpacking
+
+### After `composer require`
+
+By default, recipes are automatically unpacked after running `composer require`
+for a recipe package:
+
+```bash
+composer require drupal/example_recipe
+```
+
+This will:
+1. Download the recipe and its dependencies
+2. Add the recipe's dependencies to your project's root `composer.json`
+3. Remove the recipe itself from your dependencies
+4. Update your `composer.lock` file
+
+### After `composer create-project`
+
+Recipes are always automatically unpacked when creating a new project from a
+template that requires this plugin:
+
+```bash
+composer create-project drupal/recommended-project my-project
+```
+
+Any recipes included in the project template will be unpacked during
+installation, as long as the plugin is enabled.
+
+## Configuration
+
+Configuration options are set in the `extra` section of your `composer.json`
+file:
+
+```json
+{
+  "extra": {
+    "drupal-recipe-unpack": {
+      "ignore": ["drupal/recipe_to_ignore"],
+      "on-require": true
+    }
+  }
+}
+```
+
+### Available Options
+
+| Option | Type | Default | Description |
+|--------|------|---------|-------------|
+| `ignore` | array | `[]` | List of recipe packages to exclude from unpacking |
+| `on-require` | boolean | `true` | Automatically unpack recipes when required by `composer require` |
+
+## How Recipe Unpacking Works
+
+1. The system identifies packages of type `drupal-recipe` during installation
+2. For each recipe not in the ignore list, it:
+   - Extracts its dependencies
+   - Adds them to the root `composer.json`
+   - Recursively processes any dependencies that are also recipes
+   - Removes the recipe and any dependencies that are also recipes from the root
+     `composer.json`
+3. Updates all necessary Composer files:
+   - `composer.json`
+   - `composer.lock`
+   - `vendor/composer/installed.json`
+   - `vendor/composer/installed.php`
+
+## Cases Where Recipes Will Not Be Unpacked
+
+Recipes will **not** be unpacked in the following scenarios:
+
+1. **Explicit Ignore List**: If the recipe is listed in the `ignore` array in
+   your `extra.drupal-recipe-unpack` configuration
+   ```json
+   {
+     "extra": {
+       "drupal-recipe-unpack": {
+         "ignore": ["drupal/recipe_name"]
+       }
+     }
+   }
+   ```
+
+2. **Disabled Automatic Unpacking**: If `on-require` is set to `false` in your
+   `extra.drupal-recipe-unpack` configuration
+   ```json
+   {
+     "extra": {
+       "drupal-recipe-unpack": {
+         "on-require": false
+       }
+     }
+   }
+   ```
+
+3. **Development Dependencies**: Recipes in the `require-dev` section are not
+   automatically unpacked
+   ```json
+   {
+     "require-dev": {
+       "drupal/dev_recipe": "^1.0"
+     }
+   }
+   ```
+   You will need to manually unpack these using the `drupal:recipe-unpack`
+   command if desired.
+
+4. **With `--no-install` Option**: When using `composer require` with the
+   `--no-install` flag
+   ```bash
+   composer require drupal/example_recipe --no-install
+   ```
+   In this case, you'll need to run `composer install` afterward and then
+   manually unpack using the `drupal:recipe-unpack` command.
+
+## Example Usage Scenarios
+
+### Basic Recipe Installation
+
+```bash
+# This will automatically install and unpack the recipe
+composer require drupal/example_recipe
+```
+
+The result:
+- Dependencies from `drupal/example_recipe` are added to your root
+  `composer.json`
+- `drupal/example_recipe` itself is removed from your dependencies
+- You'll see a message: "drupal/example_recipe unpacked successfully."
+- The recipe files will be present in the drupal-recipe installer path
+
+### Manual Recipe Unpacking
+
+```bash
+# First require the recipe without unpacking
+composer require drupal/example_recipe --no-install
+composer install
+
+# Then manually unpack it
+composer drupal:recipe-unpack drupal/example_recipe
+```
+
+### Working with Dev Recipes
+
+```bash
+# This won't automatically unpack (dev dependencies aren't auto-unpacked)
+composer require --dev drupal/dev_recipe
+
+# You'll need to manually unpack if desired (with confirmation prompt)
+composer drupal:recipe-unpack drupal/dev_recipe
+```
+
+### Creating a New Project with Recipes
+
+```bash
+composer create-project drupal/recipe-based-project my-project
+```
+
+Any recipes included in the project template will be automatically unpacked
+during installation.
+
+## Best Practices
+
+1. **Review Recipe Contents**: Before requiring a recipe, review its
+   dependencies to understand what will be added to your project.
+
+2. **Consider Versioning**: When a recipe is unpacked, its version constraints
+   for dependencies are merged with your existing constraints, which may result
+   in complex version requirements.
+
+3. **Dev Dependencies**: Be cautious when unpacking development recipes, as
+   their dependencies will be moved to the main `require` section, not
+   `require-dev`.
+
+4. **Custom Recipes**: When creating custom recipes, ensure they have the
+   correct package type `drupal-recipe` and include appropriate dependencies.
+
+## Troubleshooting
+
+### Recipe Not Unpacking
+
+- Check if the package type is `drupal-recipe`
+- Verify it's not in your ignore list
+- Confirm it's not in `require-dev` (which requires manual unpacking)
+- Ensure you haven't used the `--no-install` flag without following up with
+  installation and manual unpacking
+
+### Unpacking Errors
+
+If you encounter issues during unpacking:
+
+1. Check Composer's error output for specific issues and run commands with the
+   `--verbose` flag
+2. Verify that version constraints between your existing dependencies and the
+   recipe's dependencies are compatible
+3. For manual troubleshooting, consider temporarily setting `on-require` to
+   `false` and unpacking recipes one by one

vendor/drupal/core-recipe-unpack/RootComposer.php

@@ -0,0 +1,161 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Composer;
+use Composer\Factory;
+use Composer\IO\IOInterface;
+use Composer\Json\JsonFile;
+use Composer\Json\JsonManipulator;
+use Composer\Package\Locker;
+use Composer\Package\RootPackageInterface;
+
+/**
+ * Provides access to and manipulation of the root composer files.
+ *
+ * @internal
+ */
+final class RootComposer {
+
+  /**
+   * The JSON manipulator for the contents of the root composer.json.
+   */
+  private JsonManipulator $composerManipulator;
+
+  /**
+   * The locked root composer.json content.
+   *
+   * @var array<string, mixed>|null
+   */
+  private ?array $composerLockedContent = NULL;
+
+  public function __construct(
+    private readonly Composer $composer,
+    private readonly IOInterface $io,
+  ) {}
+
+  /**
+   * Retrieves the JSON manipulator for the contents of the root composer.json.
+   *
+   * @return \Composer\Json\JsonManipulator
+   *   The JSON manipulator.
+   */
+  public function getComposerManipulator(): JsonManipulator {
+    $this->composerManipulator ??= new JsonManipulator(file_get_contents(Factory::getComposerFile()));
+    return $this->composerManipulator;
+  }
+
+  /**
+   * Gets the locked root composer.json content.
+   *
+   * @return array<string, mixed>
+   *   The locked root composer.json content.
+   */
+  public function getComposerLockedContent(): array {
+    $this->composerLockedContent ??= $this->composer->getLocker()->getLockData();
+    return $this->composerLockedContent;
+  }
+
+  /**
+   * Removes an element from the composer lock.
+   *
+   * @param string $key
+   *   The key of the element to remove.
+   * @param string $index
+   *   The index of the element to remove.
+   */
+  public function removeFromComposerLock(string $key, string $index): void {
+    unset($this->composerLockedContent[$key][$index]);
+  }
+
+  /**
+   * Adds an element to the composer lock.
+   *
+   * @param string $key
+   *   The key of the element to add.
+   * @param array $data
+   *   The data to add.
+   */
+  public function addToComposerLock(string $key, array $data): void {
+    $this->composerLockedContent[$key][] = $data;
+  }
+
+  /**
+   * Writes the root composer files.
+   *
+   * The files written are:
+   *   - composer.json
+   *   - composer.lock
+   *   - vendor/composer/installed.json
+   *   - vendor/composer/installed.php
+   *
+   * @throws \RuntimeException
+   *   If the root composer could not be updated.
+   */
+  public function writeFiles(): void {
+    // Write composer.json.
+    $composer_json = Factory::getComposerFile();
+    $composer_content = $this->getComposerManipulator()->getContents();
+    if (!file_put_contents($composer_json, $composer_content)) {
+      throw new \RuntimeException(sprintf('Could not update %s', $composer_json));
+    }
+
+    // Create package lists for lock file update.
+    $local_repo = $this->composer->getRepositoryManager()->getLocalRepository();
+    $packages = $dev_packages = [];
+    $dev_package_names = $local_repo->getDevPackageNames();
+    foreach ($local_repo->getPackages() as $package) {
+      if (in_array($package->getName(), $dev_package_names, TRUE)) {
+        $dev_packages[] = $package;
+      }
+      else {
+        $packages[] = $package;
+      }
+    }
+
+    $lock_file_path = Factory::getLockFile(Factory::getComposerFile());
+    $lock_file = new JsonFile($lock_file_path, io: $this->io);
+    $old_locker = $this->composer->getLocker();
+    $locker = new Locker($this->io, $lock_file, $this->composer->getInstallationManager(), $composer_content);
+    $composer_locker_content = $this->getComposerLockedContent();
+
+    // Write the lock file.
+    $locker->setLockData(
+      $packages,
+      $dev_packages,
+      $composer_locker_content['platform'],
+      $composer_locker_content['platform-dev'],
+      $composer_locker_content['aliases'],
+      $old_locker->getMinimumStability(),
+      $old_locker->getStabilityFlags(),
+      $old_locker->getPreferStable(),
+      $old_locker->getPreferLowest(),
+      $old_locker->getPlatformOverrides(),
+    );
+    $this->composer->setLocker($locker);
+
+    // Update installed.json and installed.php.
+    $local_repo->write($local_repo->getDevMode() ?? TRUE, $this->composer->getInstallationManager());
+
+    $this->io->write("Unpacking has updated the root composer files.", verbosity: IOInterface::VERBOSE);
+
+    assert(self::checkRootPackage($composer_content, $this->composer->getPackage()), 'Composer root package and composer.json match');
+  }
+
+  /**
+   * Checks that the composer content and root package match.
+   *
+   * @param string $composer_content
+   *   The root composer content.
+   * @param \Composer\Package\RootPackageInterface $root_package
+   *   The root package.
+   *
+   * @return bool
+   *   TRUE if the composer content and root package match, FALSE if not.
+   */
+  private static function checkRootPackage(string $composer_content, RootPackageInterface $root_package): bool {
+    $composer = JsonFile::parseJson($composer_content);
+    return empty(array_diff_key($root_package->getRequires(), $composer['require'] ?? [])) && empty(array_diff_key($root_package->getDevRequires(), $composer['require-dev'] ?? []));
+  }
+
+}

vendor/drupal/core-recipe-unpack/SemVer.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Semver\Constraint\MatchNoneConstraint;
+use Composer\Semver\Constraint\MultiConstraint;
+use Composer\Semver\Intervals;
+use Composer\Semver\VersionParser;
+
+/**
+ * Helper class to manipulate semantic versioning constraints.
+ *
+ * @internal
+ */
+final class SemVer {
+
+  private function __construct() {}
+
+  /**
+   * Minimizes two constraints.
+   *
+   * Compares two constraints and determines if one is a subset of the other. If
+   * this is the case, the constraint that is a subset is returned. For example,
+   * if called with '^6.2' and '^6.3' the function will return '^6.3'. If
+   * neither constraint is a subset then the constraints are compacted and the
+   * intersection is returned. For example, if called with ">=10.3" and
+   * "^10.4 || ^11" the function will return ">=10.4.0.0-dev, <12.0.0.0-dev".
+   *
+   * @param \Composer\Semver\VersionParser $version_parser
+   *   A version parser.
+   * @param string $constraint_a
+   *   A constraint to compact.
+   * @param string $constraint_b
+   *   A constraint to compact.
+   *
+   * @return string
+   *   The compacted constraint.
+   *
+   * @throws \LogicException
+   *   Thrown when the provided constraints have no intersection.
+   */
+  public static function minimizeConstraints(VersionParser $version_parser, string $constraint_a, string $constraint_b): string {
+    $constraint_object_a = $version_parser->parseConstraints($constraint_a);
+    $constraint_object_b = $version_parser->parseConstraints($constraint_b);
+    if (Intervals::isSubsetOf($constraint_object_a, $constraint_object_b)) {
+      return $constraint_a;
+    }
+    if (Intervals::isSubsetOf($constraint_object_b, $constraint_object_a)) {
+      return $constraint_b;
+    }
+    $constraint = Intervals::compactConstraint(new MultiConstraint([$constraint_object_a, $constraint_object_b]));
+    if ($constraint instanceof MatchNoneConstraint) {
+      throw new \LogicException(sprintf('The constraints "%s" and "%s" do not intersect and cannot be minimized.', $constraint_a, $constraint_b));
+    }
+    return sprintf(
+      '%s%s, %s%s',
+      $constraint->getLowerBound()->isInclusive() ? '>=' : '>',
+      $constraint->getLowerBound()->getVersion(),
+      $constraint->getUpperBound()->isInclusive() ? '<=' : '<',
+      $constraint->getUpperBound()->getVersion()
+    );
+  }
+
+}

vendor/drupal/core-recipe-unpack/UnpackCollection.php

@@ -0,0 +1,104 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Package\PackageInterface;
+
+/**
+ * A collection with packages to unpack.
+ *
+ * @internal
+ */
+final class UnpackCollection implements \Iterator, \Countable {
+
+  /**
+   * The queue of packages to unpack.
+   *
+   * @var \Composer\Package\PackageInterface[]
+   */
+  private array $packagesToUnpack = [];
+
+  /**
+   * The list of packages that have been unpacked.
+   *
+   * @var array<string, \Composer\Package\PackageInterface>
+   */
+  private array $unpackedPackages = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function rewind(): void {
+    reset($this->packagesToUnpack);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function current(): PackageInterface|false {
+    return current($this->packagesToUnpack);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function key(): ?string {
+    return key($this->packagesToUnpack);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function next(): void {
+    next($this->packagesToUnpack);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function valid(): bool {
+    return current($this->packagesToUnpack) !== FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function count(): int {
+    return count($this->packagesToUnpack);
+  }
+
+  /**
+   * Adds a package to the queue of packages to unpack.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package to add to the queue.
+   */
+  public function add(PackageInterface $package): self {
+    $this->packagesToUnpack[$package->getUniqueName()] = $package;
+    return $this;
+  }
+
+  /**
+   * Marks a package as unpacked.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package that has been unpacked.
+   */
+  public function markPackageUnpacked(PackageInterface $package): void {
+    $this->unpackedPackages[$package->getUniqueName()] = $package;
+  }
+
+  /**
+   * Checks if a package has been unpacked, or it's queued for unpacking.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package to check.
+   *
+   * @return bool
+   *   TRUE if the package has been unpacked.
+   */
+  public function isUnpacked(PackageInterface $package): bool {
+    return isset($this->unpackedPackages[$package->getUniqueName()]);
+  }
+
+}

vendor/drupal/core-recipe-unpack/UnpackCommand.php

@@ -0,0 +1,113 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Command\BaseCommand;
+use Composer\Package\PackageInterface;
+use Composer\Repository\PlatformRepository;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * The "drupal:recipe-unpack" command class.
+ *
+ * Manually run the unpack operation that normally happens after
+ * 'composer require'.
+ *
+ * @internal
+ */
+final class UnpackCommand extends BaseCommand {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function configure(): void {
+    $name = 'drupal:recipe-unpack';
+    $this
+      ->setName($name)
+      ->setDescription('Unpack Drupal recipes.')
+      ->addArgument('recipes', InputArgument::IS_ARRAY, "A list of recipe package names separated by a space, e.g. drupal/recipe_one drupal/recipe_two. If not provided, all recipes listed in the require section of the root composer are unpacked.")
+      ->setHelp(
+        <<<EOT
+The <info>$name</info> command unpacks dependencies from the specified recipe
+packages into the composer.json file.
+
+<info>php composer.phar $name drupal/my-recipe [...]</info>
+
+It is usually not necessary to call <info>$name</info> manually,
+because by default it is called automatically as needed, after a
+<info>require</info> command.
+EOT
+            );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function execute(InputInterface $input, OutputInterface $output): int {
+    $composer = $this->requireComposer();
+    $io = $this->getIO();
+    $local_repo = $composer->getRepositoryManager()->getLocalRepository();
+    $package_names = $input->getArgument('recipes') ?? [];
+
+    // If no recipes are provided unpack all recipes that are required by the
+    // root package.
+    if (empty($package_names)) {
+      foreach ($composer->getPackage()->getRequires() as $link) {
+        $target = $link->getTarget();
+        // Skip platform requirements, since those don't resolve to a real
+        // package.
+        // @see https://getcomposer.org/doc/articles/composer-platform-dependencies.md
+        if (PlatformRepository::isPlatformPackage($target)) {
+          continue;
+        }
+        $package = $local_repo->findPackage($target, $link->getConstraint());
+        if ($package->getType() === Plugin::RECIPE_PACKAGE_TYPE) {
+          $package_names[] = $package->getName();
+        }
+      }
+      if (empty($package_names)) {
+        $io->write('<info>No recipes to unpack.</info>');
+        return 0;
+      }
+    }
+
+    $manager = new UnpackManager($composer, $io);
+    $unpack_collection = new UnpackCollection();
+    foreach ($package_names as $package_name) {
+      if (!$manager->isRootDependency($package_name)) {
+        $io->error(sprintf('<info>%s</info> not found in the root composer.json.', $package_name));
+        return 1;
+      }
+      $packages = $local_repo->findPackages($package_name);
+      $package = reset($packages);
+
+      if (!$package instanceof PackageInterface) {
+        $io->error(sprintf('<info>%s</info> does not resolve to a package.', $package_name));
+        return 1;
+      }
+
+      if ($package->getType() !== Plugin::RECIPE_PACKAGE_TYPE) {
+        $io->error(sprintf('<info>%s</info> is not a recipe.', $package->getPrettyName()));
+        return 1;
+      }
+
+      if ($manager->unpackOptions->isIgnored($package)) {
+        $io->error(sprintf('<info>%s</info> is in the extra.drupal-recipe-unpack.ignore list.', $package->getName()));
+        return 1;
+      }
+
+      if (UnpackManager::isDevRequirement($package)) {
+        $io->warning(sprintf('<info>%s</info> is present in the require-dev key. Unpacking will move the recipe\'s dependencies to the require key.', $package->getName()));
+        if ($io->isInteractive() && !$io->askConfirmation('<info>Do you want to continue</info> [<comment>yes</comment>]?')) {
+          return 0;
+        }
+      }
+      $unpack_collection->add($package);
+    }
+    $manager->unpack($unpack_collection);
+    return 0;
+  }
+
+}

vendor/drupal/core-recipe-unpack/UnpackManager.php

@@ -0,0 +1,99 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Composer;
+use Composer\InstalledVersions;
+use Composer\IO\IOInterface;
+use Composer\Package\PackageInterface;
+use Composer\Semver\Intervals;
+
+/**
+ * Manages the recipe unpacking process.
+ *
+ * @internal
+ */
+final readonly class UnpackManager {
+
+  /**
+   * The root composer with the root dependencies to be manipulated.
+   */
+  private RootComposer $rootComposer;
+
+  /**
+   * The unpack options.
+   */
+  public UnpackOptions $unpackOptions;
+
+  public function __construct(
+    private Composer $composer,
+    private IOInterface $io,
+  ) {
+    $this->rootComposer = new RootComposer($composer, $io);
+    $this->unpackOptions = UnpackOptions::create($composer->getPackage()->getExtra());
+  }
+
+  /**
+   * Unpacks the packages in the provided collection.
+   *
+   * @param \Drupal\Composer\Plugin\RecipeUnpack\UnpackCollection $unpackCollection
+   *   The collection of recipe packages to unpack.
+   */
+  public function unpack(UnpackCollection $unpackCollection): void {
+    if (count($unpackCollection) === 0) {
+      // Early return to avoid unnecessary work.
+      return;
+    }
+
+    foreach ($unpackCollection as $package) {
+      $unpacker = new Unpacker(
+        $package,
+        $this->composer,
+        $this->rootComposer,
+        $unpackCollection,
+        $this->unpackOptions,
+        $this->io,
+      );
+      $unpacker->unpackDependencies();
+      $this->io->write("<info>{$package->getName()}</info> unpacked.");
+    }
+
+    // Unpacking uses \Composer\Semver\Intervals::isSubsetOf() to choose between
+    // constraints.
+    Intervals::clear();
+
+    $this->rootComposer->writeFiles();
+  }
+
+  /**
+   * Determines if the provided package is present in the root composer.json.
+   *
+   * @param string $package_name
+   *   The package name to check.
+   *
+   * @return bool
+   *   TRUE if the package is present in the root composer.json, FALSE if not.
+   */
+  public function isRootDependency(string $package_name): bool {
+    $root_package = $this->composer->getPackage();
+    return isset($root_package->getRequires()[$package_name]) || isset($root_package->getDevRequires()[$package_name]);
+  }
+
+  /**
+   * Checks if a package is a dev requirement.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package to check.
+   *
+   * @return bool
+   *   TRUE if the package is present in require-dev or due to a package in
+   *   require-dev, FALSE if not.
+   */
+  public static function isDevRequirement(PackageInterface $package): bool {
+    // Check if package is either a regular or dev requirement.
+    return InstalledVersions::isInstalled($package->getName()) &&
+      // Check if package is a regular requirement.
+      !InstalledVersions::isInstalled($package->getName(), FALSE);
+  }
+
+}

vendor/drupal/core-recipe-unpack/UnpackOptions.php

@@ -0,0 +1,79 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Package\PackageInterface;
+
+/**
+ * Per-project options from the 'extras' section of the composer.json file.
+ *
+ * Projects that implement dependency unpacking plugin can further configure it.
+ * This data is pulled from the 'drupal-recipe-unpack' portion of the extras
+ * section.
+ *
+ * @code
+ *  "extras": {
+ *    "drupal-recipe-unpack": {
+ *      "ignore": ["drupal/recipe_name"],
+ *      "on-require": true
+ *    }
+ *  }
+ * @endcode
+ *
+ * Supported options:
+ * - `ignore` (array):
+ *   Specifies packages to exclude from unpacking into the root composer.json.
+ * - `on-require` (boolean):
+ *   Whether to unpack recipes automatically on require.
+ *
+ * @internal
+ */
+final readonly class UnpackOptions {
+
+  /**
+   * The ID of the extra section in the top-level composer.json file.
+   */
+  const string ID = 'drupal-recipe-unpack';
+
+  /**
+   * The raw data from the 'extras' section of the top-level composer.json file.
+   *
+   * @var array{ignore: string[], on-require: boolean}
+   */
+  public array $options;
+
+  private function __construct(array $options) {
+    $this->options = $options + [
+      'ignore' => [],
+      'on-require' => TRUE,
+    ];
+  }
+
+  /**
+   * Checks if a package should be ignored.
+   *
+   * @param \Composer\Package\PackageInterface $package
+   *   The package.
+   *
+   * @return bool
+   *   TRUE if the package should be ignored, FALSE if not.
+   */
+  public function isIgnored(PackageInterface $package): bool {
+    return in_array($package->getName(), $this->options['ignore'], TRUE);
+  }
+
+  /**
+   * Creates an unpack options object.
+   *
+   * @param array $extras
+   *   The contents of the 'extras' section.
+   *
+   * @return self
+   *   The unpack options object representing the provided unpack options
+   */
+  public static function create(array $extras): self {
+    $options = $extras[self::ID] ?? [];
+    return new self($options);
+  }
+
+}

vendor/drupal/core-recipe-unpack/Unpacker.php

@@ -0,0 +1,217 @@
+<?php
+
+namespace Drupal\Composer\Plugin\RecipeUnpack;
+
+use Composer\Composer;
+use Composer\IO\IOInterface;
+use Composer\Package\Link;
+use Composer\Package\PackageInterface;
+use Composer\Semver\VersionParser;
+
+/**
+ * Handles the details of unpacking a specific recipe.
+ *
+ * @internal
+ */
+final readonly class Unpacker {
+
+  /**
+   * The version parser.
+   */
+  private VersionParser $versionParser;
+
+  public function __construct(
+    private PackageInterface $package,
+    private Composer $composer,
+    private RootComposer $rootComposer,
+    private UnpackCollection $unpackCollection,
+    private UnpackOptions $unpackOptions,
+    private IOInterface $io,
+  ) {
+    $this->versionParser = new VersionParser();
+  }
+
+  /**
+   * Unpacks the package's dependencies to the root composer.json and lock file.
+   */
+  public function unpackDependencies(): void {
+    $this->updateComposerJsonPackages();
+    $this->updateComposerLockContent();
+    $this->unpackCollection->markPackageUnpacked($this->package);
+  }
+
+  /**
+   * Processes dependencies of the package that is being unpacked.
+   *
+   * If the dependency is a recipe and should be unpacked, we add it into the
+   * package queue so that it will be unpacked as well. If the dependency is not
+   * a recipe, or an ignored recipe, the package link will be yielded.
+   *
+   * @param array<string, \Composer\Package\Link> $package_dependency_links
+   *   The package dependencies to process.
+   *
+   * @return iterable<\Composer\Package\Link>
+   *   The package dependencies to add to composer.json.
+   */
+  private function processPackageDependencies(array $package_dependency_links): iterable {
+    foreach ($package_dependency_links as $link) {
+      if ($link->getTarget() === $this->package->getName()) {
+        // This dependency is the same as the current package, so let's skip it.
+        continue;
+      }
+
+      $package = $this->getPackageFromLinkTarget($link);
+
+      // If we can't find the package in the local repository that's because it
+      // has already been removed therefore skip it.
+      if ($package === NULL) {
+        continue;
+      }
+
+      if ($package->getType() === Plugin::RECIPE_PACKAGE_TYPE) {
+        if ($this->unpackCollection->isUnpacked($package)) {
+          // This dependency is already unpacked.
+          continue;
+        }
+
+        if (!$this->unpackOptions->isIgnored($package)) {
+          // This recipe should be unpacked as well.
+          $this->unpackCollection->add($package);
+          continue;
+        }
+        else {
+          // This recipe should not be unpacked. But it might need to be added
+          // to the root composer.json
+          $this->io->write(sprintf('<info>%s</info> not unpacked because it is ignored.', $package->getName()), verbosity: IOInterface::VERBOSE);
+        }
+      }
+
+      yield $link;
+    }
+  }
+
+  /**
+   * Updates the composer.json content with the package being unpacked.
+   *
+   * This method will add all the package dependencies to the root composer.json
+   * content and also remove the package itself from the root composer.json.
+   *
+   * @throws \RuntimeException
+   *   If the composer.json could not be updated.
+   */
+  private function updateComposerJsonPackages(): void {
+    $composer_manipulator = $this->rootComposer->getComposerManipulator();
+    $composer_config = $this->composer->getConfig();
+    $sort_packages = $composer_config->get('sort-packages');
+    $root_package = $this->composer->getPackage();
+    $root_requires = $root_package->getRequires();
+    $root_dev_requires = $root_package->getDevRequires();
+
+    foreach ($this->processPackageDependencies($this->package->getRequires()) as $package_dependency) {
+      $dependency_name = $package_dependency->getTarget();
+      $recipe_constraint_string = $package_dependency->getPrettyConstraint();
+      if (isset($root_requires[$dependency_name])) {
+        $recipe_constraint_string = SemVer::minimizeConstraints($this->versionParser, $recipe_constraint_string, $root_requires[$dependency_name]->getPrettyConstraint());
+        if ($recipe_constraint_string === $root_requires[$dependency_name]) {
+          // This dependency is already in the required section with the
+          // correct constraint.
+          continue;
+        }
+      }
+      elseif (isset($root_dev_requires[$dependency_name])) {
+        $recipe_constraint_string = SemVer::minimizeConstraints($this->versionParser, $recipe_constraint_string, $root_dev_requires[$dependency_name]->getPrettyConstraint());
+        // This dependency is already in the require-dev section. We will
+        // move it to the require section.
+        $composer_manipulator->removeSubNode('require-dev', $dependency_name);
+      }
+
+      // Add the dependency to the required section. If it cannot be added, then
+      // throw an exception.
+      if (!$composer_manipulator->addLink(
+          'require',
+          $dependency_name,
+          $recipe_constraint_string,
+          $sort_packages,
+      )) {
+        throw new \RuntimeException(sprintf('Unable to manipulate composer.json during the unpack of %s',
+          $dependency_name,
+        ));
+      }
+      $link = new Link($root_package->getName(), $dependency_name, $this->versionParser->parseConstraints($recipe_constraint_string), Link::TYPE_REQUIRE, $recipe_constraint_string);
+      $root_requires[$dependency_name] = $link;
+      unset($root_dev_requires[$dependency_name]);
+      $this->io->write(sprintf('Adding <info>%s</info> (<comment>%s</comment>) to composer.json during the unpack of <info>%s</info>', $dependency_name, $recipe_constraint_string, $this->package->getName()), verbosity: IOInterface::VERBOSE);
+    }
+
+    // Ensure the written packages are no longer in the dev package names.
+    $local_repo = $this->composer->getRepositoryManager()->getLocalRepository();
+    $local_repo->setDevPackageNames(array_diff($local_repo->getDevPackageNames(), array_keys($root_requires)));
+
+    // Update the root package to reflect the changes.
+    $root_package->setDevRequires($root_dev_requires);
+    $root_package->setRequires($root_requires);
+
+    $composer_manipulator->removeSubNode(UnpackManager::isDevRequirement($this->package) ? 'require-dev' : 'require', $this->package->getName());
+    $this->io->write(sprintf('Removing <info>%s</info> from composer.json', $this->package->getName()), verbosity: IOInterface::VERBOSE);
+
+    $composer_manipulator->removeMainKeyIfEmpty('require-dev');
+  }
+
+  /**
+   * Updates the composer.lock content and keeps the local repo in sync.
+   *
+   * This method will remove the package itself from the composer.lock content
+   * in the root composer.
+   */
+  private function updateComposerLockContent(): void {
+    $composer_locker_content = $this->rootComposer->getComposerLockedContent();
+    $root_package = $this->composer->getPackage();
+    $root_requires = $root_package->getRequires();
+    $root_dev_requires = $root_package->getDevRequires();
+    $local_repo = $this->composer->getRepositoryManager()->getLocalRepository();
+
+    if (isset($root_requires[$this->package->getName()])) {
+      unset($root_requires[$this->package->getName()]);
+      $root_package->setRequires($root_requires);
+    }
+
+    foreach ($composer_locker_content['packages'] as $key => $lock_data) {
+      // Find the package being unpacked in the composer.lock content and
+      // remove it.
+      if ($lock_data['name'] === $this->package->getName()) {
+        $this->rootComposer->removeFromComposerLock('packages', $key);
+        // If the package is in require-dev we need to move the lock data.
+        if (isset($root_dev_requires[$lock_data['name']])) {
+          $this->rootComposer->addToComposerLock('packages-dev', $lock_data);
+          $dev_package_names = $local_repo->getDevPackageNames();
+          $dev_package_names[] = $lock_data['name'];
+          $local_repo->setDevPackageNames($dev_package_names);
+          return;
+        }
+        break;
+      }
+    }
+    $local_repo->setDevPackageNames(array_diff($local_repo->getDevPackageNames(), [$this->package->getName()]));
+    $local_repo->removePackage($this->package);
+    if (isset($root_dev_requires[$this->package->getName()])) {
+      unset($root_dev_requires[$this->package->getName()]);
+      $root_package->setDevRequires($root_dev_requires);
+    }
+  }
+
+  /**
+   * Gets the package object from a link's target.
+   *
+   * @param \Composer\Package\Link $dependency
+   *   The link dependency.
+   *
+   * @return \Composer\Package\PackageInterface|null
+   *   The package object.
+   */
+  private function getPackageFromLinkTarget(Link $dependency): ?PackageInterface {
+    return $this->composer->getRepositoryManager()
+      ->getLocalRepository()
+      ->findPackage($dependency->getTarget(), $dependency->getConstraint());
+  }
+
+}

vendor/drupal/core-recipe-unpack/composer.json

@@ -0,0 +1,26 @@
+{
+  "name": "drupal/core-recipe-unpack",
+  "description": "A Composer project unpacker for Drupal recipes.",
+  "type": "composer-plugin",
+  "keywords": ["drupal"],
+  "homepage": "https://www.drupal.org/project/drupal",
+  "license": "GPL-2.0-or-later",
+  "require": {
+    "composer-plugin-api": "^2",
+    "php": ">=8.3"
+  },
+  "autoload": {
+    "psr-4": {
+      "Drupal\\Composer\\Plugin\\RecipeUnpack\\": ""
+    }
+  },
+  "extra": {
+    "class": "Drupal\\Composer\\Plugin\\RecipeUnpack\\Plugin"
+  },
+  "config": {
+    "sort-packages": true
+  },
+  "require-dev": {
+    "composer/composer": "^2.7"
+  }
+}