diff --git a/composer.json b/composer.json
index 9ce7358439..ba39243944 100644
--- a/composer.json
+++ b/composer.json
@@ -50,8 +50,6 @@
     "scripts": {
         "pre-autoload-dump": "Drupal\\Core\\Composer\\Composer::preAutoloadDump",
         "post-autoload-dump": "Drupal\\Core\\Composer\\Composer::ensureHtaccess",
-        "post-package-install": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
-        "post-package-update": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
         "drupal-phpunit-upgrade-check": "Drupal\\Core\\Composer\\Composer::upgradePHPUnit",
         "drupal-phpunit-upgrade": "@composer update phpunit/phpunit phpspec/prophecy symfony/yaml --with-dependencies --no-progress",
         "phpcs": "phpcs --standard=core/phpcs.xml.dist --runtime-set installed_paths $($COMPOSER_BINARY config vendor-dir)/drupal/coder/coder_sniffer --",
@@ -62,5 +60,8 @@
             "type": "composer",
             "url": "https://packages.drupal.org/8"
         }
-    ]
+    ],
+    "require-dev": {
+        "composer/composer": "^1.8"
+    }
 }
diff --git a/composer.lock b/composer.lock
index 41e5a866f1..7d5e540e67 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "d764df12b2cff2be49d45e95ecbeb5d7",
+    "content-hash": "d893afc1da2c9fa30925841809a51e05",
     "packages": [
         {
             "name": "asm89/stack-cors",
@@ -3026,6 +3026,247 @@
             ],
             "time": "2018-01-07T19:17:08+00:00"
         },
+        {
+            "name": "composer/ca-bundle",
+            "version": "1.1.3",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/composer/ca-bundle.git",
+                "reference": "8afa52cd417f4ec417b4bfe86b68106538a87660"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/composer/ca-bundle/zipball/8afa52cd417f4ec417b4bfe86b68106538a87660",
+                "reference": "8afa52cd417f4ec417b4bfe86b68106538a87660",
+                "shasum": ""
+            },
+            "require": {
+                "ext-openssl": "*",
+                "ext-pcre": "*",
+                "php": "^5.3.2 || ^7.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.5",
+                "psr/log": "^1.0",
+                "symfony/process": "^2.5 || ^3.0 || ^4.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Composer\\CaBundle\\": "src"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be",
+                    "homepage": "http://seld.be"
+                }
+            ],
+            "description": "Lets you find a path to the system CA bundle, and includes a fallback to the Mozilla CA bundle.",
+            "keywords": [
+                "cabundle",
+                "cacert",
+                "certificate",
+                "ssl",
+                "tls"
+            ],
+            "time": "2018-10-18T06:09:13+00:00"
+        },
+        {
+            "name": "composer/composer",
+            "version": "1.8.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/composer/composer.git",
+                "reference": "d8aef3af866b28786ce9b8647e52c42496436669"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/composer/composer/zipball/d8aef3af866b28786ce9b8647e52c42496436669",
+                "reference": "d8aef3af866b28786ce9b8647e52c42496436669",
+                "shasum": ""
+            },
+            "require": {
+                "composer/ca-bundle": "^1.0",
+                "composer/semver": "^1.0",
+                "composer/spdx-licenses": "^1.2",
+                "composer/xdebug-handler": "^1.1",
+                "justinrainbow/json-schema": "^3.0 || ^4.0 || ^5.0",
+                "php": "^5.3.2 || ^7.0",
+                "psr/log": "^1.0",
+                "seld/jsonlint": "^1.4",
+                "seld/phar-utils": "^1.0",
+                "symfony/console": "^2.7 || ^3.0 || ^4.0",
+                "symfony/filesystem": "^2.7 || ^3.0 || ^4.0",
+                "symfony/finder": "^2.7 || ^3.0 || ^4.0",
+                "symfony/process": "^2.7 || ^3.0 || ^4.0"
+            },
+            "conflict": {
+                "symfony/console": "2.8.38"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.8.35 || ^5.7",
+                "phpunit/phpunit-mock-objects": "^2.3 || ^3.0"
+            },
+            "suggest": {
+                "ext-openssl": "Enabling the openssl extension allows you to access https URLs for repositories and packages",
+                "ext-zip": "Enabling the zip extension allows you to unzip archives",
+                "ext-zlib": "Allow gzip compression of HTTP requests"
+            },
+            "bin": [
+                "bin/composer"
+            ],
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.8-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Composer\\": "src/Composer"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Nils Adermann",
+                    "email": "naderman@naderman.de",
+                    "homepage": "http://www.naderman.de"
+                },
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be",
+                    "homepage": "http://seld.be"
+                }
+            ],
+            "description": "Composer helps you declare, manage and install dependencies of PHP projects, ensuring you have the right stack everywhere.",
+            "homepage": "https://getcomposer.org/",
+            "keywords": [
+                "autoload",
+                "dependency",
+                "package"
+            ],
+            "time": "2018-12-03T09:31:16+00:00"
+        },
+        {
+            "name": "composer/spdx-licenses",
+            "version": "1.5.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/composer/spdx-licenses.git",
+                "reference": "7a9556b22bd9d4df7cad89876b00af58ef20d3a2"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/composer/spdx-licenses/zipball/7a9556b22bd9d4df7cad89876b00af58ef20d3a2",
+                "reference": "7a9556b22bd9d4df7cad89876b00af58ef20d3a2",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.3.2 || ^7.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.5",
+                "phpunit/phpunit-mock-objects": "2.3.0 || ^3.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Composer\\Spdx\\": "src"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Nils Adermann",
+                    "email": "naderman@naderman.de",
+                    "homepage": "http://www.naderman.de"
+                },
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be",
+                    "homepage": "http://seld.be"
+                },
+                {
+                    "name": "Rob Bast",
+                    "email": "rob.bast@gmail.com",
+                    "homepage": "http://robbast.nl"
+                }
+            ],
+            "description": "SPDX licenses list and validation library.",
+            "keywords": [
+                "license",
+                "spdx",
+                "validator"
+            ],
+            "time": "2018-11-01T09:45:54+00:00"
+        },
+        {
+            "name": "composer/xdebug-handler",
+            "version": "1.3.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/composer/xdebug-handler.git",
+                "reference": "dc523135366eb68f22268d069ea7749486458562"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/composer/xdebug-handler/zipball/dc523135366eb68f22268d069ea7749486458562",
+                "reference": "dc523135366eb68f22268d069ea7749486458562",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.3.2 || ^7.0",
+                "psr/log": "^1.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.5"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "Composer\\XdebugHandler\\": "src"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "John Stevenson",
+                    "email": "john-stevenson@blueyonder.co.uk"
+                }
+            ],
+            "description": "Restarts a process without xdebug.",
+            "keywords": [
+                "Xdebug",
+                "performance"
+            ],
+            "time": "2018-11-29T10:59:02+00:00"
+        },
         {
             "name": "doctrine/instantiator",
             "version": "1.0.5",
@@ -3088,6 +3329,12 @@
                 "url": "https://git.drupal.org/project/coder.git",
                 "reference": "984c54a7b1e8f27ff1c32348df69712afd86b17f"
             },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/klausi/coder/zipball/984c54a7b1e8f27ff1c32348df69712afd86b17f",
+                "reference": "984c54a7b1e8f27ff1c32348df69712afd86b17f",
+                "shasum": ""
+            },
             "require": {
                 "ext-mbstring": "*",
                 "php": ">=5.4.0",
@@ -3382,6 +3629,72 @@
             ],
             "time": "2016-10-04T09:27:04+00:00"
         },
+        {
+            "name": "justinrainbow/json-schema",
+            "version": "5.2.7",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/justinrainbow/json-schema.git",
+                "reference": "8560d4314577199ba51bf2032f02cd1315587c23"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/justinrainbow/json-schema/zipball/8560d4314577199ba51bf2032f02cd1315587c23",
+                "reference": "8560d4314577199ba51bf2032f02cd1315587c23",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.3"
+            },
+            "require-dev": {
+                "friendsofphp/php-cs-fixer": "^2.1",
+                "json-schema/json-schema-test-suite": "1.2.0",
+                "phpunit/phpunit": "^4.8.35"
+            },
+            "bin": [
+                "bin/validate-json"
+            ],
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "5.0.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "JsonSchema\\": "src/JsonSchema/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Bruno Prieto Reis",
+                    "email": "bruno.p.reis@gmail.com"
+                },
+                {
+                    "name": "Justin Rainbow",
+                    "email": "justin.rainbow@gmail.com"
+                },
+                {
+                    "name": "Igor Wiedler",
+                    "email": "igor@wiedler.ch"
+                },
+                {
+                    "name": "Robert Schönthal",
+                    "email": "seroscho@googlemail.com"
+                }
+            ],
+            "description": "A library to validate a json schema.",
+            "homepage": "https://github.com/justinrainbow/json-schema",
+            "keywords": [
+                "json",
+                "schema"
+            ],
+            "time": "2018-02-14T22:26:30+00:00"
+        },
         {
             "name": "mikey179/vfsStream",
             "version": "v1.6.5",
@@ -4288,6 +4601,99 @@
             "homepage": "https://github.com/sebastianbergmann/version",
             "time": "2015-06-21T13:59:46+00:00"
         },
+        {
+            "name": "seld/jsonlint",
+            "version": "1.7.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/Seldaek/jsonlint.git",
+                "reference": "d15f59a67ff805a44c50ea0516d2341740f81a38"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/Seldaek/jsonlint/zipball/d15f59a67ff805a44c50ea0516d2341740f81a38",
+                "reference": "d15f59a67ff805a44c50ea0516d2341740f81a38",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^5.3 || ^7.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.0"
+            },
+            "bin": [
+                "bin/jsonlint"
+            ],
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "Seld\\JsonLint\\": "src/Seld/JsonLint/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be",
+                    "homepage": "http://seld.be"
+                }
+            ],
+            "description": "JSON Linter",
+            "keywords": [
+                "json",
+                "linter",
+                "parser",
+                "validator"
+            ],
+            "time": "2018-01-24T12:46:19+00:00"
+        },
+        {
+            "name": "seld/phar-utils",
+            "version": "1.0.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/Seldaek/phar-utils.git",
+                "reference": "7009b5139491975ef6486545a39f3e6dad5ac30a"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/Seldaek/phar-utils/zipball/7009b5139491975ef6486545a39f3e6dad5ac30a",
+                "reference": "7009b5139491975ef6486545a39f3e6dad5ac30a",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Seld\\PharUtils\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Jordi Boggiano",
+                    "email": "j.boggiano@seld.be"
+                }
+            ],
+            "description": "PHAR file format utilities, for when PHP phars you up",
+            "keywords": [
+                "phra"
+            ],
+            "time": "2015-10-13T18:44:15+00:00"
+        },
         {
             "name": "squizlabs/php_codesniffer",
             "version": "2.8.1",
@@ -4533,6 +4939,105 @@
             "homepage": "https://symfony.com",
             "time": "2018-07-26T10:03:52+00:00"
         },
+        {
+            "name": "symfony/filesystem",
+            "version": "v4.2.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/filesystem.git",
+                "reference": "2f4c8b999b3b7cadb2a69390b01af70886753710"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/filesystem/zipball/2f4c8b999b3b7cadb2a69390b01af70886753710",
+                "reference": "2f4c8b999b3b7cadb2a69390b01af70886753710",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.1.3",
+                "symfony/polyfill-ctype": "~1.8"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "4.2-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\Filesystem\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony Filesystem Component",
+            "homepage": "https://symfony.com",
+            "time": "2018-11-11T19:52:12+00:00"
+        },
+        {
+            "name": "symfony/finder",
+            "version": "v4.2.1",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/finder.git",
+                "reference": "e53d477d7b5c4982d0e1bfd2298dbee63d01441d"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/finder/zipball/e53d477d7b5c4982d0e1bfd2298dbee63d01441d",
+                "reference": "e53d477d7b5c4982d0e1bfd2298dbee63d01441d",
+                "shasum": ""
+            },
+            "require": {
+                "php": "^7.1.3"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "4.2-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\Finder\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony Finder Component",
+            "homepage": "https://symfony.com",
+            "time": "2018-11-11T19:52:12+00:00"
+        },
         {
             "name": "symfony/phpunit-bridge",
             "version": "v3.4.15",
diff --git a/core/composer.json b/core/composer.json
index 8dfd8a10f2..a59df438a6 100644
--- a/core/composer.json
+++ b/core/composer.json
@@ -194,6 +194,7 @@
                 "core/lib/Drupal/Component/Plugin/composer.json",
                 "core/lib/Drupal/Component/ProxyBuilder/composer.json",
                 "core/lib/Drupal/Component/Render/composer.json",
+                "core/lib/Drupal/Component/Scaffold/composer.json",
                 "core/lib/Drupal/Component/Serialization/composer.json",
                 "core/lib/Drupal/Component/Transliteration/composer.json",
                 "core/lib/Drupal/Component/Utility/composer.json",
diff --git a/core/drupalci.yml b/core/drupalci.yml
index 2085b9737b..c01c31ffe2 100644
--- a/core/drupalci.yml
+++ b/core/drupalci.yml
@@ -3,17 +3,6 @@
 # https://www.drupal.org/drupalorg/docs/drupal-ci/customizing-drupalci-testing
 build:
   assessment:
-    validate_codebase:
-      phplint:
-      csslint:
-        halt-on-fail: false
-      eslint:
-        # A test must pass eslinting standards check in order to continue processing.
-        halt-on-fail: false
-      phpcs:
-        # phpcs will use core's specified version of Coder.
-        sniff-all-files: false
-        halt-on-fail: false
     testing:
       # run_tests task is executed several times in order of performance speeds.
       # halt-on-fail can be set on the run_tests tasks in order to fail fast.
@@ -24,27 +13,3 @@ build:
         testgroups: '--all'
         suppress-deprecations: false
         halt-on-fail: false
-      run_tests.kernel:
-        types: 'PHPUnit-Kernel'
-        testgroups: '--all'
-        suppress-deprecations: false
-        halt-on-fail: false
-      run_tests.simpletest:
-         types: 'Simpletest'
-         testgroups: '--all'
-         suppress-deprecations: false
-         halt-on-fail: false
-      run_tests.functional:
-        types: 'PHPUnit-Functional'
-        testgroups: '--all'
-        suppress-deprecations: false
-        halt-on-fail: false
-      run_tests.javascript:
-        concurrency: 15
-        types: 'PHPUnit-FunctionalJavascript'
-        testgroups: '--all'
-        suppress-deprecations: false
-        halt-on-fail: false
-      # Run nightwatch testing.
-      # @see https://www.drupal.org/project/drupal/issues/2869825
-      nightwatchjs:
diff --git a/core/lib/Drupal/Component/Scaffold/CommandProvider.php b/core/lib/Drupal/Component/Scaffold/CommandProvider.php
new file mode 100644
index 0000000000..22350a9b97
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/CommandProvider.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Drupal\Component\Scaffold;
+
+use Composer\Plugin\Capability\CommandProvider as CommandProviderCapability;
+
+/**
+ * Lists composer commands provided by this package.
+ */
+class CommandProvider implements CommandProviderCapability {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCommands() {
+    return [
+      new DrupalScaffoldCommand(),
+    ];
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Scaffold/DrupalScaffoldCommand.php b/core/lib/Drupal/Component/Scaffold/DrupalScaffoldCommand.php
new file mode 100644
index 0000000000..14498bf7c8
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/DrupalScaffoldCommand.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\Component\Scaffold;
+
+use Composer\Command\BaseCommand;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * The "drupal:scaffold" command class.
+ *
+ * Downloads scaffold files and generates the autoload.php file.
+ */
+class DrupalScaffoldCommand extends BaseCommand {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function configure() {
+    parent::configure();
+    $this
+      ->setName('drupal:scaffold')
+      ->setDescription('Update the Drupal scaffold files.');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function execute(InputInterface $input, OutputInterface $output) {
+    $handler = new Handler($this->getComposer(), $this->getIO());
+    $handler->downloadScaffold();
+    // Generate the autoload.php file after generating the scaffold files.
+    $handler->generateAutoload();
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Scaffold/FileFetcher.php b/core/lib/Drupal/Component/Scaffold/FileFetcher.php
new file mode 100644
index 0000000000..c5907427ff
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/FileFetcher.php
@@ -0,0 +1,136 @@
+<?php
+
+namespace Drupal\Component\Scaffold;
+
+use Composer\IO\IOInterface;
+use Composer\Util\Filesystem;
+use Composer\Util\RemoteFilesystem;
+
+/**
+ * Downloads all required files and writes them to the file system.
+ */
+class FileFetcher {
+
+  /**
+   * Composer utility to retrieve remote files.
+   *
+   * @var \Composer\Util\RemoteFilesystem
+   */
+  protected $remoteFilesystem;
+
+  /**
+   * The composer IO object for printing messages to the console.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * A boolean indicating if progress should be displayed.
+   *
+   * @var bool
+   */
+  protected $progress;
+
+  /**
+   * The url pattern where scaffold files may be retrieved.
+   *
+   * @var string
+   */
+  protected $source;
+
+  /**
+   * Array of filenames to fetch from the source repository.
+   *
+   * @var array
+   */
+  protected $filenames;
+
+  /**
+   * Composer utility for working with the local filesystem.
+   *
+   * @var \Composer\Util\Filesystem
+   */
+  protected $fs;
+
+  /**
+   * Constructs this FileFetcher object.
+   *
+   * @param \Composer\Util\RemoteFilesystem $remoteFilesystem
+   *   Composer utility to retrieve remote files.
+   * @param string $source
+   *   The url pattern where scaffold files may be retrieved.
+   * @param \Composer\IO\IOInterface $io
+   *   The composer IO object for printing messages to the console.
+   * @param bool $progress
+   *   A boolean indicating if progress should be displayed.
+   */
+  public function __construct(RemoteFilesystem $remoteFilesystem, $source, IOInterface $io, $progress = TRUE) {
+    $this->remoteFilesystem = $remoteFilesystem;
+    $this->io = $io;
+    $this->source = $source;
+    // TODO: this should be injectable.
+    $this->fs = new Filesystem();
+    $this->progress = $progress;
+  }
+
+  /**
+   * Downloads all required files and writes it to the file system.
+   *
+   * @param string $version
+   *   The version of the scaffold file to be retrieved.
+   * @param string $destination
+   *   The location on the filesystem where we will place the file.
+   * @param bool $override
+   *   Whether the file should be overridden or left in place.
+   */
+  public function fetch($version, $destination, $override) {
+    foreach ($this->filenames as $sourceFilename => $filename) {
+      $target = "$destination/$filename";
+      if ($override || !file_exists($target)) {
+        $url = $this->getUri($sourceFilename, $version);
+        $this->fs->ensureDirectoryExists($destination . '/' . dirname($filename));
+        if ($this->progress) {
+          $this->io->writeError("  - <info>$filename</info> (<comment>$url</comment>): ", FALSE);
+          $this->remoteFilesystem->copy($url, $url, $target, $this->progress);
+          // Used to put a new line because the remote file system does not put
+          // one.
+          $this->io->writeError('');
+        }
+        else {
+          $this->remoteFilesystem->copy($url, $url, $target, $this->progress);
+        }
+      }
+    }
+  }
+
+  /**
+   * Set filenames.
+   *
+   * @param array $filenames
+   *   An array of filenames to retrieve from the drupal git repository.
+   */
+  public function setFilenames(array $filenames) {
+    $this->filenames = $filenames;
+  }
+
+  /**
+   * Replace filename and version in the source pattern with their values.
+   *
+   * @param string $filename
+   *   The filename to retrieve.
+   * @param string $version
+   *   The version of the git drupal repository.
+   *
+   * @return string
+   *   A uri of the filename/version combination.
+   */
+  protected function getUri($filename, $version) {
+    $map = [
+      '{path}' => $filename,
+      '{version}' => $version,
+    ];
+    return str_replace(array_keys($map), array_values($map), $this->source);
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Scaffold/Handler.php b/core/lib/Drupal/Component/Scaffold/Handler.php
new file mode 100644
index 0000000000..5aeaac64fa
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/Handler.php
@@ -0,0 +1,649 @@
+<?php
+
+namespace Drupal\Component\Scaffold;
+
+use Composer\DependencyResolver\Operation\OperationInterface;
+use Composer\Script\Event;
+use Composer\Installer\PackageEvent;
+use Composer\Plugin\CommandEvent;
+use Composer\Composer;
+use Composer\DependencyResolver\Operation\InstallOperation;
+use Composer\DependencyResolver\Operation\UpdateOperation;
+use Composer\EventDispatcher\EventDispatcher;
+use Composer\IO\IOInterface;
+use Composer\Package\PackageInterface;
+use Composer\Util\Filesystem;
+use Composer\Util\RemoteFilesystem;
+use Symfony\Component\Filesystem\Filesystem as SymfonyFilesystem;
+
+/**
+ * Primary class of the plugin that determines which files should be fetched.
+ */
+class Handler {
+
+  /**
+   * Defines a composer event that fires prior to building the scaffold.
+   */
+  const PRE_DRUPAL_SCAFFOLD_CMD = 'pre-drupal-scaffold-cmd';
+
+  /**
+   * Defines a composer event that fires after the scaffold is built.
+   */
+  const POST_DRUPAL_SCAFFOLD_CMD = 'post-drupal-scaffold-cmd';
+
+  /**
+   * The Composer application object.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * The composer IO object for printing messages to the console.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * A boolean indicating if progress should be displayed.
+   *
+   * @var bool
+   */
+  protected $progress;
+
+  /**
+   * Composer package for drupal/core.
+   *
+   * @var \Composer\Package\PackageInterface
+   */
+  protected $drupalCorePackage;
+
+  /**
+   * Array of core's dependencies' unwanted folders.
+   *
+   * @var array
+   */
+  protected static $packageToCleanup = [
+    'behat/mink' => ['tests', 'driver-testsuite'],
+    'behat/mink-browserkit-driver' => ['tests'],
+    'behat/mink-goutte-driver' => ['tests'],
+    'drupal/coder' => ['coder_sniffer/Drupal/Test', 'coder_sniffer/DrupalPractice/Test'],
+    'doctrine/cache' => ['tests'],
+    'doctrine/collections' => ['tests'],
+    'doctrine/common' => ['tests'],
+    'doctrine/inflector' => ['tests'],
+    'doctrine/instantiator' => ['tests'],
+    'egulias/email-validator' => ['documentation', 'tests'],
+    'fabpot/goutte' => ['Goutte/Tests'],
+    'guzzlehttp/promises' => ['tests'],
+    'guzzlehttp/psr7' => ['tests'],
+    'jcalderonzumba/gastonjs' => ['docs', 'examples', 'tests'],
+    'jcalderonzumba/mink-phantomjs-driver' => ['tests'],
+    'masterminds/html5' => ['test'],
+    'mikey179/vfsStream' => ['src/test'],
+    'paragonie/random_compat' => ['tests'],
+    'phpdocumentor/reflection-docblock' => ['tests'],
+    'phpunit/php-code-coverage' => ['tests'],
+    'phpunit/php-timer' => ['tests'],
+    'phpunit/php-token-stream' => ['tests'],
+    'phpunit/phpunit' => ['tests'],
+    'phpunit/php-mock-objects' => ['tests'],
+    'sebastian/comparator' => ['tests'],
+    'sebastian/diff' => ['tests'],
+    'sebastian/environment' => ['tests'],
+    'sebastian/exporter' => ['tests'],
+    'sebastian/global-state' => ['tests'],
+    'sebastian/recursion-context' => ['tests'],
+    'stack/builder' => ['tests'],
+    'symfony/browser-kit' => ['Tests'],
+    'symfony/class-loader' => ['Tests'],
+    'symfony/console' => ['Tests'],
+    'symfony/css-selector' => ['Tests'],
+    'symfony/debug' => ['Tests'],
+    'symfony/dependency-injection' => ['Tests'],
+    'symfony/dom-crawler' => ['Tests'],
+    // @see \Drupal\Tests\Component\EventDispatcher\ContainerAwareEventDispatcherTest
+    // 'symfony/event-dispatcher' => ['Tests'],
+    'symfony/http-foundation' => ['Tests'],
+    'symfony/http-kernel' => ['Tests'],
+    'symfony/process' => ['Tests'],
+    'symfony/psr-http-message-bridge' => ['Tests'],
+    'symfony/routing' => ['Tests'],
+    'symfony/serializer' => ['Tests'],
+    'symfony/translation' => ['Tests'],
+    'symfony/validator' => ['Tests', 'Resources'],
+    'symfony/yaml' => ['Tests'],
+    'symfony-cmf/routing' => ['Test', 'Tests'],
+    'twig/twig' => ['doc', 'ext', 'test'],
+  ];
+
+  /**
+   * Handler constructor.
+   *
+   * @param \Composer\Composer $composer
+   *   The primary composer application object.
+   * @param \Composer\IO\IOInterface $io
+   *   The composer IO object for printing messages to the console.
+   */
+  public function __construct(Composer $composer, IOInterface $io) {
+    $this->composer = $composer;
+    $this->io = $io;
+    $this->progress = TRUE;
+
+    // Pre-load all of the plugins classes so that when we update the
+    // drupal/drupal-scaffold plugin itself, we do not run into issues with
+    // api mismatches between versions.
+    $this->manualLoad();
+  }
+
+  /**
+   * Pre-load all of our sources on initial load.
+   *
+   * This ensures that we will not get a more recent version of one of
+   * our classes e.g. after a 'composer update' operation.
+   */
+  protected function manualLoad() {
+    $src_dir = __DIR__;
+
+    $classes = [
+      'CommandProvider',
+      'DrupalScaffoldCommand',
+      'FileFetcher',
+      'PrestissimoFileFetcher',
+    ];
+
+    foreach ($classes as $src) {
+      if (!class_exists('\\Drupal\\Component\\Scaffold\\' . $src)) {
+        include "{$src_dir}/{$src}.php";
+      }
+    }
+  }
+
+  /**
+   * Determines if drupal/core is being changed by the install or update.
+   *
+   * @param \Composer\DependencyResolver\Operation\OperationInterface $operation
+   *   Determines what type of Composer package operation is occurring.
+   *
+   * @return mixed
+   *   Returns 'drupal/core' if core is being updated, otherwise returns null.
+   */
+  protected function getCorePackage(OperationInterface $operation) {
+    if ($operation instanceof InstallOperation) {
+      $package = $operation->getPackage();
+    }
+    elseif ($operation instanceof UpdateOperation) {
+      $package = $operation->getTargetPackage();
+    }
+    if (isset($package) && $package instanceof PackageInterface && $package->getName() == 'drupal/core') {
+      return $package;
+    }
+    return NULL;
+  }
+
+  /**
+   * Get the command options.
+   *
+   * @param \Composer\Plugin\CommandEvent $event
+   *   The Composer event that called this listener.
+   */
+  public function onCmdBeginsEvent(CommandEvent $event) {
+    if ($event->getInput()->hasOption('no-progress')) {
+      $this->progress = !($event->getInput()->getOption('no-progress'));
+    }
+    else {
+      $this->progress = TRUE;
+    }
+  }
+
+  /**
+   * Event handler that fires after an install or update command.
+   *
+   * Files to be processed are marked, and potentially problematic test files
+   * are removed from vendor packages.
+   *
+   * @param \Composer\Installer\PackageEvent $event
+   *   The install or update event object from Composer.
+   */
+  public function onPostPackageEvent(PackageEvent $event) {
+    $package = $this->getCorePackage($event->getOperation());
+    if ($package) {
+      // By explicitly setting the core package, the onPostCmdEvent() will
+      // process the scaffolding automatically.
+      $this->drupalCorePackage = $package;
+    }
+
+    $vendor_dir = $event->getComposer()->getConfig()->get('vendor-dir');
+    $io = $event->getIO();
+
+    // Get target package if we're updating, package otherwise.
+    $operation = $event->getOperation();
+    if ($operation->getJobType() == 'update') {
+      $package = $operation->getTargetPackage();
+    }
+    else {
+      $package = $operation->getPackage();
+    }
+
+    // Get the case-adjusted package name, which is also the path to the package
+    // within the vendor directory.
+    $package_name = static::findPackageKey($package->getName());
+    if ($package_name) {
+      $cleanup_paths = static::$packageToCleanup[$package_name];
+      static::doTestCodeCleanup($vendor_dir, $package_name, $cleanup_paths, $io);
+    }
+  }
+
+  /**
+   * Post install command event to execute the scaffolding.
+   *
+   * @param \Composer\Script\Event $event
+   *   The Composer event.
+   */
+  public function onPostCmdEvent(Event $event) {
+    // Only install the scaffolding if drupal/core was installed,
+    // AND there are no scaffolding files present.
+    if (isset($this->drupalCorePackage)) {
+      $this->downloadScaffold();
+      // Generate the autoload.php file after generating the scaffold files.
+      $this->generateAutoload();
+    }
+  }
+
+  /**
+   * Downloads drupal scaffold files for the current process.
+   */
+  public function downloadScaffold() {
+    $drupal_core_package = $this->getDrupalCorePackage();
+    $webroot = realpath($this->getWebRoot());
+
+    // Collect options, excludes and settings files.
+    $options = $this->getOptions();
+    $files = array_diff($this->getIncludes(), $this->getExcludes());
+
+    // Call any pre-scaffold scripts that may be defined.
+    $dispatcher = new EventDispatcher($this->composer, $this->io);
+    $dispatcher->dispatch(self::PRE_DRUPAL_SCAFFOLD_CMD);
+
+    $version = $this->getDrupalCoreVersion($drupal_core_package);
+
+    $remoteFs = new RemoteFilesystem($this->io);
+
+    $fetcher = new PrestissimoFileFetcher($remoteFs, $options['source'], $this->io, $this->progress, $this->composer->getConfig());
+    $fetcher->setFilenames(array_combine($files, $files));
+    $fetcher->fetch($version, $webroot, TRUE);
+
+    $fetcher->setFilenames($this->getInitial());
+    $fetcher->fetch($version, $webroot, FALSE);
+
+    // Call post-scaffold scripts.
+    $dispatcher->dispatch(self::POST_DRUPAL_SCAFFOLD_CMD);
+  }
+
+  /**
+   * Generate the autoload file at the Drupal root.
+   *
+   * Include the autoload file that Composer generated.
+   */
+  public function generateAutoload() {
+    $vendor_path = $this->getVendorPath();
+    $webroot = $this->getWebRoot();
+
+    // Calculate the relative path from the webroot (location of the
+    // project autoload.php) to the vendor directory.
+    $fs = new SymfonyFilesystem();
+    $relative_vendor_path = $fs->makePathRelative($vendor_path, realpath($webroot));
+
+    $fs->dumpFile($webroot . "/autoload.php", $this->autoLoadContents($relative_vendor_path));
+  }
+
+  /**
+   * Build the contents of the docroot autoload file.
+   *
+   * This allows the vendor directory to live outside of the docroot.
+   *
+   * @param string $relativeVendorPath
+   *   Path to the vendor directory, relative to the Drupal root.
+   *
+   * @return string
+   *   The contents of the autoload.php for the docroot directory.
+   */
+  protected function autoLoadContents($relativeVendorPath) {
+    $relativeVendorPath = rtrim($relativeVendorPath, '/');
+
+    $autoload_contents = <<<EOF
+<?php
+
+/**
+ * @file
+ * Includes the autoloader created by Composer.
+ *
+ * @see composer.json
+ * @see index.php
+ * @see core/install.php
+ * @see core/rebuild.php
+ * @see core/modules/statistics/statistics.php
+ */
+
+return require __DIR__ . '/$relativeVendorPath/autoload.php';
+
+EOF;
+    return $autoload_contents;
+  }
+
+  /**
+   * Get the path to the 'vendor' directory.
+   *
+   * @return string
+   *   The full path to the vendor directory.
+   */
+  public function getVendorPath() {
+    $config = $this->composer->getConfig();
+    $filesystem = new Filesystem();
+    $filesystem->ensureDirectoryExists($config->get('vendor-dir'));
+    $vendor_path = $filesystem->normalizePath(realpath($config->get('vendor-dir')));
+
+    return $vendor_path;
+  }
+
+  /**
+   * Returns the drupal core package object.
+   *
+   * Look up the Drupal core package object, or return it from where we cached
+   * it in the $drupalCorePackage field.
+   *
+   * @return \Composer\Package\PackageInterface
+   *   Composer package for drupal/core.
+   */
+  public function getDrupalCorePackage() {
+    if (!isset($this->drupalCorePackage)) {
+      $this->drupalCorePackage = $this->getPackage('drupal/core');
+    }
+    return $this->drupalCorePackage;
+  }
+
+  /**
+   * Returns the Drupal core version for the given package.
+   *
+   * @param \Composer\Package\PackageInterface $drupalCorePackage
+   *   The Composer package for drupal/core.
+   *
+   * @return string
+   *   The version number of drupal/core in this installation.
+   */
+  protected function getDrupalCoreVersion(PackageInterface $drupalCorePackage) {
+    $version = $drupalCorePackage->getPrettyVersion();
+    if ($drupalCorePackage->getStability() == 'dev' && substr($version, -4) == '-dev') {
+      $version = substr($version, 0, -4);
+      return $version;
+    }
+    return $version;
+  }
+
+  /**
+   * Retrieve the path to the web root.
+   *
+   * @return string
+   *   The webroot. Well, actually, the drupal root.
+   */
+  public function getWebRoot() {
+    $drupal_core_package = $this->getDrupalCorePackage();
+    $installation_manager = $this->composer->getInstallationManager();
+    $core_path = $installation_manager->getInstallPath($drupal_core_package);
+    // Webroot is the parent path of the drupal core installation path.
+    $webroot = dirname($core_path);
+
+    return $webroot;
+  }
+
+  /**
+   * Retrieve a package from the current composer process.
+   *
+   * @param string $name
+   *   Name of the package to get from the current composer installation.
+   *
+   * @return \Composer\Package\PackageInterface
+   *   A Composer Package matching the given name.
+   */
+  protected function getPackage($name) {
+    return $this->composer->getRepositoryManager()->getLocalRepository()->findPackage($name, '*');
+  }
+
+  /**
+   * Retrieve excludes from optional "extra" configuration.
+   *
+   * @return string[]
+   *   Any scaffold files that we would like to exclude from the default config.
+   */
+  protected function getExcludes() {
+    return $this->getNamedOptionList('excludes', 'getExcludesDefault');
+  }
+
+  /**
+   * Retrieve list of additional files from optional "extra" configuration.
+   *
+   * @return string[]
+   *   Additional scaffold files we want to retrieve.
+   */
+  protected function getIncludes() {
+    return $this->getNamedOptionList('includes', 'getIncludesDefault');
+  }
+
+  /**
+   * Retrieve list of initial files from optional "extra" configuration.
+   *
+   * @return string[]
+   *   A list of files that should only be scaffolded on primary installation.
+   */
+  protected function getInitial() {
+    return $this->getNamedOptionList('initial', 'getInitialDefault');
+  }
+
+  /**
+   * Gets a configuration value from extra config for drupal-scaffold.
+   *
+   * Retrieve a named list of options from optional "extra" configuration.
+   * Respects 'omit-defaults', and either includes or does not include the
+   * default values, as requested.
+   *
+   * @param string $optionName
+   *   The particular option value to retrieve.
+   * @param string $defaultFn
+   *   Function to gather defaults from for this option.
+   *
+   * @return string[]
+   *   Array of defined values in the extra config.
+   */
+  protected function getNamedOptionList($optionName, $defaultFn) {
+    $options = $this->getOptions();
+    $result = [];
+    if (empty($options['omit-defaults'])) {
+      $result = $this->$defaultFn();
+    }
+    $result = array_merge($result, (array) $options[$optionName]);
+
+    return $result;
+  }
+
+  /**
+   * Retrieve excludes from optional "extra" configuration.
+   *
+   * The 'source' option is the url pattern where we locate the files, e.g.
+   * Github: https://raw.githubusercontent.com/drupal/drupal/{version}/{path}
+   * Drupal.org: https://cgit.drupalcode.org/drupal/plain/{path}?h={version}
+   *
+   * @return string[]
+   *   An array of plugin configuration options.
+   */
+  protected function getOptions() {
+    $extra = $this->composer->getPackage()->getExtra() + ['drupal-scaffold' => []];
+    $options = $extra['drupal-scaffold'] + [
+      'omit-defaults' => FALSE,
+      'excludes' => [],
+      'includes' => [],
+      'initial' => [],
+      'source' => 'https://cgit.drupalcode.org/drupal/plain/{path}?h={version}',
+    ];
+    return $options;
+  }
+
+  /**
+   * Holds default excludes.
+   *
+   * @return string[]
+   *   Nothing is excluded by default.
+   */
+  protected function getExcludesDefault() {
+    return [];
+  }
+
+  /**
+   * Holds default settings files list.
+   *
+   * @return string[]
+   *   The default scaffolding files that come with drupal.
+   */
+  protected function getIncludesDefault() {
+
+    $common = [
+      '.csslintrc',
+      '.editorconfig',
+      '.eslintignore',
+      '.eslintrc.json',
+      '.gitattributes',
+      '.ht.router.php',
+      '.htaccess',
+      'autoload.php',
+      'example.gitignore',
+      'index.php',
+      'INSTALL.txt',
+      'README.txt',
+      'robots.txt',
+      'update.php',
+      'web.config',
+      'modules/README.txt',
+      'profiles/README.txt',
+      'sites/default/default.settings.php',
+      'sites/default/default.services.yml',
+      'sites/development.services.yml',
+      'sites/example.settings.local.php',
+      'sites/example.sites.php',
+      'sites/README.txt',
+      'themes/README.txt',
+    ];
+
+    sort($common);
+    return $common;
+  }
+
+  /**
+   * Holds default initial files.
+   *
+   * @return string[]
+   *   Empty array for no initial default.
+   */
+  protected function getInitialDefault() {
+    return [];
+  }
+
+  /**
+   * Remove possibly problematic test files from a single vendor package.
+   *
+   * @param string $vendor_dir
+   *   Full path to the vendor directory.
+   * @param string $package_path
+   *   The package path within the vendor directory. Should also happen to be
+   *   the package name. Example: psr/log.
+   * @param string[] $cleanup_paths
+   *   An array of relative paths within the vendor path which should be
+   *   removed.
+   * @param \Composer\IO\IOInterface $io
+   *   IO object provided by Composer.
+   */
+  protected static function doTestCodeCleanup($vendor_dir, $package_path, array $cleanup_paths, IOInterface $io) {
+    $package_dir = $vendor_dir . '/' . $package_path;
+    if (is_dir($package_dir)) {
+      $io->write(sprintf("    Test code cleanup for <comment>%s</comment>", $package_path), TRUE, $io::VERY_VERBOSE);
+      foreach ($cleanup_paths as $cleanup_path) {
+        $cleanup_dir = $package_dir . '/' . $cleanup_path;
+        if (is_dir($cleanup_dir)) {
+          // Try to clean up.
+          if (static::deleteRecursive($cleanup_dir)) {
+            $io->write(sprintf("      <info>Removing directory '%s'</info>", $cleanup_path), TRUE, $io::VERY_VERBOSE);
+          }
+          else {
+            // Always display a message if this fails as it means something
+            // has gone wrong. Therefore the message has to include the
+            // package name as the first informational message might not
+            // exist.
+            $io->write(sprintf("      <error>Failure removing directory '%s'</error> in package <comment>%s</comment>.", $cleanup_path, $package_path), TRUE, IOInterface::NORMAL);
+          }
+        }
+        else {
+          // If the package has changed or the --prefer-dist version does not
+          // include the directory this is not an error.
+          $io->write(sprintf("      Directory '%s' does not exist", $cleanup_dir), TRUE, $io::VERY_VERBOSE);
+        }
+      }
+      $io->write('', TRUE, $io::VERY_VERBOSE);
+    }
+  }
+
+  /**
+   * Find the array key for a given package name with a case-insensitive search.
+   *
+   * @param string $package_name
+   *   The package name from composer. This is always already lower case.
+   *
+   * @return string|null
+   *   The string key, or NULL if none was found.
+   */
+  protected static function findPackageKey($package_name) {
+    $package_key = NULL;
+    // In most cases the package name is already used as the array key.
+    if (isset(static::$packageToCleanup[$package_name])) {
+      $package_key = $package_name;
+    }
+    else {
+      // Handle any mismatch in case between the package name and array key.
+      // For example, the array key 'mikey179/vfsStream' needs to be found
+      // when composer returns a package name of 'mikey179/vfsstream'.
+      foreach (static::$packageToCleanup as $key => $dirs) {
+        if (strtolower($key) === $package_name) {
+          $package_key = $key;
+          break;
+        }
+      }
+    }
+    return $package_key;
+  }
+
+  /**
+   * Helper method to remove directories and the files they contain.
+   *
+   * @param string $path
+   *   The directory or file to remove. It must exist.
+   *
+   * @return bool
+   *   TRUE on success or FALSE on failure.
+   */
+  protected static function deleteRecursive($path) {
+    if (is_file($path) || is_link($path)) {
+      return unlink($path);
+    }
+    $success = TRUE;
+    $dir = dir($path);
+    while (($entry = $dir->read()) !== FALSE) {
+      if ($entry == '.' || $entry == '..') {
+        continue;
+      }
+      $entry_path = $path . '/' . $entry;
+      $success = static::deleteRecursive($entry_path) && $success;
+    }
+    $dir->close();
+
+    return rmdir($path) && $success;
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Scaffold/LICENSE.txt b/core/lib/Drupal/Component/Scaffold/LICENSE.txt
new file mode 100644
index 0000000000..94fb84639c
--- /dev/null
+++ b/core/lib/Drupal/Component/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.
diff --git a/core/lib/Drupal/Component/Scaffold/Plugin.php b/core/lib/Drupal/Component/Scaffold/Plugin.php
new file mode 100644
index 0000000000..81f27d8ea2
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/Plugin.php
@@ -0,0 +1,92 @@
+<?php
+
+namespace Drupal\Component\Scaffold;
+
+use Composer\Script\Event;
+use Composer\Plugin\CommandEvent;
+use Composer\Composer;
+use Composer\EventDispatcher\EventSubscriberInterface;
+use Composer\Installer\PackageEvent;
+use Composer\Installer\PackageEvents;
+use Composer\IO\IOInterface;
+use Composer\Plugin\Capable;
+use Composer\Plugin\PluginEvents;
+use Composer\Plugin\PluginInterface;
+use Composer\Script\ScriptEvents;
+
+/**
+ * Composer plugin for handling drupal scaffold.
+ */
+class Plugin implements PluginInterface, EventSubscriberInterface, Capable {
+
+  /**
+   * Handler class that does the actual processing of the scaffolding.
+   *
+   * @var \Drupal\Component\Scaffold\Handler
+   */
+  protected $handler;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function activate(Composer $composer, IOInterface $io) {
+    // We use a separate PluginScripts object. This way we separate
+    // functionality and also avoid some debug issues with the plugin being
+    // copied on initialisation.
+    // @see \Composer\Plugin\PluginManager::registerPackage()
+    $this->handler = new Handler($composer, $io);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCapabilities() {
+    return [
+      'Composer\Plugin\Capability\CommandProvider' => 'Drupal\Component\Scaffold\CommandProvider',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      PackageEvents::POST_PACKAGE_INSTALL => 'postPackage',
+      PackageEvents::POST_PACKAGE_UPDATE => 'postPackage',
+      ScriptEvents::POST_UPDATE_CMD => 'postCmd',
+      ScriptEvents::POST_CREATE_PROJECT_CMD => 'postCmd',
+      PluginEvents::COMMAND => 'cmdBegins',
+    ];
+  }
+
+  /**
+   * Command begins event callback.
+   *
+   * @param \Composer\Plugin\CommandEvent $event
+   *   Composer event sent on command execution.
+   */
+  public function cmdBegins(CommandEvent $event) {
+    $this->handler->onCmdBeginsEvent($event);
+  }
+
+  /**
+   * Post package event behaviour.
+   *
+   * @param \Composer\Installer\PackageEvent $event
+   *   Composer package event sent on install/update/remove.
+   */
+  public function postPackage(PackageEvent $event) {
+    $this->handler->onPostPackageEvent($event);
+  }
+
+  /**
+   * Post command event callback.
+   *
+   * @param \Composer\Script\Event $event
+   *   Composer script event sent when commands are run.
+   */
+  public function postCmd(Event $event) {
+    $this->handler->onPostCmdEvent($event);
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Scaffold/PrestissimoFileFetcher.php b/core/lib/Drupal/Component/Scaffold/PrestissimoFileFetcher.php
new file mode 100644
index 0000000000..cbc4e5bb88
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/PrestissimoFileFetcher.php
@@ -0,0 +1,100 @@
+<?php
+
+namespace Drupal\Component\Scaffold;
+
+use Composer\Util\RemoteFilesystem;
+use Composer\Config;
+use Composer\IO\IOInterface;
+use Hirak\Prestissimo\CopyRequest;
+use Hirak\Prestissimo\CurlMulti;
+
+/**
+ * Extends the default FileFetcher for parallel downloads.
+ *
+ * If hirak/prestissimo is available, it will use, otherwise it will default to
+ * FileFetcher default behavior.
+ */
+class PrestissimoFileFetcher extends FileFetcher {
+
+  /**
+   * Composer configuration data.
+   *
+   * @var \Composer\Config
+   */
+  protected $config;
+
+  /**
+   * Constructs this PrestissimoFileFetcher object.
+   *
+   * @param \Composer\Util\RemoteFilesystem $remoteFilesystem
+   *   Composer utility to retrieve remote files.
+   * @param string $source
+   *   The url pattern where scaffold files may be retrieved.
+   * @param \Composer\IO\IOInterface $io
+   *   The composer IO object for printing messages to the console.
+   * @param bool $progress
+   *   A boolean indicating if progress should be displayed.
+   * @param \Composer\Config $config
+   *   Composer config.
+   */
+  public function __construct(RemoteFilesystem $remoteFilesystem, $source, IOInterface $io, $progress = TRUE, Config $config) {
+    parent::__construct($remoteFilesystem, $source, $io, $progress);
+    $this->config = $config;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fetch($version, $destination, $override) {
+    if (class_exists(CurlMulti::class)) {
+      $this->fetchWithPrestissimo($version, $destination, $override);
+      return;
+    }
+    parent::fetch($version, $destination, $override);
+  }
+
+  /**
+   * Fetch files in parallel.
+   *
+   * @param string $version
+   *   The version of the scaffold file to be retrieved.
+   * @param string $destination
+   *   The location on the filesystem where we will place the file.
+   * @param bool $override
+   *   Whether the file should be overridden or left in place.
+   */
+  protected function fetchWithPrestissimo($version, $destination, $override) {
+    $requests = [];
+
+    foreach ($this->filenames as $sourceFilename => $filename) {
+      $target = "$destination/$filename";
+      if ($override || !file_exists($target)) {
+        $url = $this->getUri($sourceFilename, $version);
+        $this->fs->ensureDirectoryExists($destination . '/' . dirname($filename));
+        $requests[] = new CopyRequest($url, $target, FALSE, $this->io, $this->config);
+      }
+    }
+
+    $successCnt = $failureCnt = 0;
+    $totalCnt = count($requests);
+    if ($totalCnt == 0) {
+      return;
+    }
+
+    $multi = new CurlMulti();
+    $multi->setRequests($requests);
+    do {
+      $multi->setupEventLoop();
+      $multi->wait();
+      $result = $multi->getFinishedResults();
+      $successCnt += $result['successCnt'];
+      $failureCnt += $result['failureCnt'];
+      if ($this->progress) {
+        foreach ($result['urls'] as $url) {
+          $this->io->writeError("  - Downloading <comment>$successCnt</comment>/<comment>$totalCnt</comment>: <info>$url</info>", TRUE);
+        }
+      }
+    } while ($multi->remain());
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Scaffold/README.md b/core/lib/Drupal/Component/Scaffold/README.md
new file mode 100644
index 0000000000..3ead55067f
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/README.md
@@ -0,0 +1,126 @@
+# drupal-scaffold
+
+Composer plugin for automatically downloading Drupal scaffold files (like
+`index.php`, `update.php`, etc) when requiring `drupal/core` via Composer.
+
+It is recommended that the vendor directory be placed in its standard location
+at the project root, outside of the Drupal root; however, the location of the
+vendor directory and the Drupal root may be placed in whatever
+location suits the project. Drupal-scaffold will generate the autoload.php
+file at the Drupal root to require the Composer-generated autoload file in the
+vendor directory.
+
+## Usage
+
+Run `composer require drupal/drupal-scaffold` in your Composer
+project before installing or updating `drupal/core`.
+
+Once drupal-scaffold is required by your project, it will automatically update
+your scaffold files whenever `composer update` changes the version of
+`drupal/core` installed.
+
+## Configuration
+
+You can configure the plugin by providing some settings in the `extra` section
+of your root `composer.json`.
+
+```json
+{
+  "extra": {
+    "drupal-scaffold": {
+      "source": "https://cgit.drupalcode.org/drupal/plain/{path}?h={version}",
+      "excludes": [
+        "google123.html",
+        "robots.txt"
+      ],
+      "includes": [
+        "sites/default/example.settings.my.php"
+      ],
+      "initial": {
+        "sites/default/default.services.yml": "sites/default/services.yml",
+        "sites/default/default.settings.php": "sites/default/settings.php"
+      },
+      "omit-defaults": false
+    }
+  }
+}
+```
+The `source` option may be used to specify the URL to download the
+scaffold files from; the default source is cgit.drupalcode.org. The literal string
+`{version}` in the `source` option is replaced with the current version of
+Drupal core being updated prior to download.
+
+With the `drupal-scaffold` option `excludes`, you can provide additional paths
+that should not be copied or overwritten. The plugin provides no excludes by
+default.
+
+Default includes are provided by the plugin:
+```
+.csslintrc
+.editorconfig
+.eslintignore
+.eslintrc.json
+.gitattributes
+.ht.router.php
+.htaccess
+example.gitignore
+index.php
+INSTALL.txt
+README.txt
+robots.txt
+modules/README.txt
+profiles/README.txt
+sites/README.txt
+sites/default/default.settings.php
+sites/default/default.services.yml
+sites/development.services.yml
+sites/example.settings.local.php
+sites/example.sites.php
+themes/README.txt
+update.php
+web.config
+```
+
+When setting `omit-defaults` to `true`, neither the default excludes nor the
+default includes will be provided; in this instance, only those files explicitly
+listed in the `excludes` and `includes` options will be considered. If
+`omit-defaults` is `false` (the default), then any items listed in `excludes`
+or `includes` will be in addition to the usual defaults.
+
+The `initial` hash lists files that should be copied over only if they do not
+exist in the destination. The key specifies the path to the source file, and
+the value indicates the path to the destination file.
+
+## Limitation
+
+When using Composer to install or update the Drupal development branch, the
+scaffold files are always taken from the HEAD of the branch (or, more
+specifically, from the most recent development .tar.gz archive). This might
+not be what you want when using an old development version (e.g. when the
+version is fixed via composer.lock). To avoid problems, always commit your
+scaffold files to the repository any time that composer.lock is committed.
+Note that the correct scaffold files are retrieved when using a tagged release
+of `drupal/core` (recommended).
+
+## Custom command
+
+The plugin by default is only downloading the scaffold files when installing or
+updating `drupal/core`. You can call it manually with "composer drupal:scaffold"
+or "@composer drupal:scaffold" in Composer Scripts.
+
+```json
+"scripts": {
+    "post-install-cmd": [
+        "@composer drupal:scaffold",
+        "..."
+    ],
+    "post-update-cmd": [
+        "@composer drupal:scaffold",
+        "..."
+    ]
+},
+```
+
+It is assumed that the scaffold files will be committed to the repository, to
+ensure that the correct files are used on the CI server (see **Limitation**,
+above). Commit the scaffold files to your repository after running `composer install` for the first time.
diff --git a/core/lib/Drupal/Component/Scaffold/TESTING.txt b/core/lib/Drupal/Component/Scaffold/TESTING.txt
new file mode 100644
index 0000000000..3186f0f901
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/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/Component.
+
+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\Component 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
diff --git a/core/lib/Drupal/Component/Scaffold/composer.json b/core/lib/Drupal/Component/Scaffold/composer.json
new file mode 100644
index 0000000000..6f77bf7ad0
--- /dev/null
+++ b/core/lib/Drupal/Component/Scaffold/composer.json
@@ -0,0 +1,27 @@
+{
+    "name": "drupal/drupal-scaffold",
+    "description": "New Composer plugin for updating the Drupal scaffold files when using drupal/core",
+    "type": "composer-plugin",
+    "license": "GPL-2.0-or-later",
+    "require": {
+        "php": ">=5.5.9",
+        "composer-plugin-api": "^1.0.0"
+    },
+    "require-dev": {
+        "composer/composer": "^1.8",
+        "symfony/process": "~3.4.0"
+    },
+    "autoload": {
+        "classmap": [
+            "CommandProvider.php",
+            "DrupalScaffoldCommand.php",
+            "FileFetcher.php",
+            "Handler.php",
+            "Plugin.php",
+            "PrestissimoFileFetcher.php"
+        ]
+    },
+    "extra": {
+        "class": "Drupal\\Component\\Scaffold\\Plugin"
+    }
+}
diff --git a/core/lib/Drupal/Core/Composer/Composer.php b/core/lib/Drupal/Core/Composer/Composer.php
index 9833b7ede1..d2f352eef8 100644
--- a/core/lib/Drupal/Core/Composer/Composer.php
+++ b/core/lib/Drupal/Core/Composer/Composer.php
@@ -15,60 +15,6 @@
  */
 class Composer {
 
-  protected static $packageToCleanup = [
-    'behat/mink' => ['tests', 'driver-testsuite'],
-    'behat/mink-browserkit-driver' => ['tests'],
-    'behat/mink-goutte-driver' => ['tests'],
-    'drupal/coder' => ['coder_sniffer/Drupal/Test', 'coder_sniffer/DrupalPractice/Test'],
-    'doctrine/cache' => ['tests'],
-    'doctrine/collections' => ['tests'],
-    'doctrine/common' => ['tests'],
-    'doctrine/inflector' => ['tests'],
-    'doctrine/instantiator' => ['tests'],
-    'egulias/email-validator' => ['documentation', 'tests'],
-    'fabpot/goutte' => ['Goutte/Tests'],
-    'guzzlehttp/promises' => ['tests'],
-    'guzzlehttp/psr7' => ['tests'],
-    'jcalderonzumba/gastonjs' => ['docs', 'examples', 'tests'],
-    'jcalderonzumba/mink-phantomjs-driver' => ['tests'],
-    'masterminds/html5' => ['test'],
-    'mikey179/vfsStream' => ['src/test'],
-    'paragonie/random_compat' => ['tests'],
-    'phpdocumentor/reflection-docblock' => ['tests'],
-    'phpunit/php-code-coverage' => ['tests'],
-    'phpunit/php-timer' => ['tests'],
-    'phpunit/php-token-stream' => ['tests'],
-    'phpunit/phpunit' => ['tests'],
-    'phpunit/php-mock-objects' => ['tests'],
-    'sebastian/comparator' => ['tests'],
-    'sebastian/diff' => ['tests'],
-    'sebastian/environment' => ['tests'],
-    'sebastian/exporter' => ['tests'],
-    'sebastian/global-state' => ['tests'],
-    'sebastian/recursion-context' => ['tests'],
-    'stack/builder' => ['tests'],
-    'symfony/browser-kit' => ['Tests'],
-    'symfony/class-loader' => ['Tests'],
-    'symfony/console' => ['Tests'],
-    'symfony/css-selector' => ['Tests'],
-    'symfony/debug' => ['Tests'],
-    'symfony/dependency-injection' => ['Tests'],
-    'symfony/dom-crawler' => ['Tests'],
-    // @see \Drupal\Tests\Component\EventDispatcher\ContainerAwareEventDispatcherTest
-    // 'symfony/event-dispatcher' => ['Tests'],
-    'symfony/http-foundation' => ['Tests'],
-    'symfony/http-kernel' => ['Tests'],
-    'symfony/process' => ['Tests'],
-    'symfony/psr-http-message-bridge' => ['Tests'],
-    'symfony/routing' => ['Tests'],
-    'symfony/serializer' => ['Tests'],
-    'symfony/translation' => ['Tests'],
-    'symfony/validator' => ['Tests', 'Resources'],
-    'symfony/yaml' => ['Tests'],
-    'symfony-cmf/routing' => ['Test', 'Tests'],
-    'twig/twig' => ['doc', 'ext', 'test'],
-  ];
-
   /**
    * Add vendor classes to Composer's static classmap.
    */
@@ -192,82 +138,16 @@ public static function upgradePHPUnitCheck($phpunit_version) {
    * @param \Composer\Installer\PackageEvent $event
    *   A PackageEvent object to get the configured composer vendor directories
    *   from.
+   *
+   * @deprecated in Drupal 8.7.0, will be removed before Drupal 9.0.0.
    */
   public static function vendorTestCodeCleanup(PackageEvent $event) {
-    $vendor_dir = $event->getComposer()->getConfig()->get('vendor-dir');
     $io = $event->getIO();
-    $op = $event->getOperation();
-    if ($op->getJobType() == 'update') {
-      $package = $op->getTargetPackage();
-    }
-    else {
-      $package = $op->getPackage();
-    }
-    $package_key = static::findPackageKey($package->getName());
-    $message = sprintf("    Processing <comment>%s</comment>", $package->getPrettyName());
+    // @todo: Add @see for change record.
+    $message = __METHOD__ . '() has been deprecated. Remove the script calls in your project composer.json';
     if ($io->isVeryVerbose()) {
-      $io->write($message);
-    }
-    if ($package_key) {
-      foreach (static::$packageToCleanup[$package_key] as $path) {
-        $dir_to_remove = $vendor_dir . '/' . $package_key . '/' . $path;
-        $print_message = $io->isVeryVerbose();
-        if (is_dir($dir_to_remove)) {
-          if (static::deleteRecursive($dir_to_remove)) {
-            $message = sprintf("      <info>Removing directory '%s'</info>", $path);
-          }
-          else {
-            // Always display a message if this fails as it means something has
-            // gone wrong. Therefore the message has to include the package name
-            // as the first informational message might not exist.
-            $print_message = TRUE;
-            $message = sprintf("      <error>Failure removing directory '%s'</error> in package <comment>%s</comment>.", $path, $package->getPrettyName());
-          }
-        }
-        else {
-          // If the package has changed or the --prefer-dist version does not
-          // include the directory this is not an error.
-          $message = sprintf("      Directory '%s' does not exist", $path);
-        }
-        if ($print_message) {
-          $io->write($message);
-        }
-      }
-
-      if ($io->isVeryVerbose()) {
-        // Add a new line to separate this output from the next package.
-        $io->write("");
-      }
-    }
-  }
-
-  /**
-   * Find the array key for a given package name with a case-insensitive search.
-   *
-   * @param string $package_name
-   *   The package name from composer. This is always already lower case.
-   *
-   * @return string|null
-   *   The string key, or NULL if none was found.
-   */
-  protected static function findPackageKey($package_name) {
-    $package_key = NULL;
-    // In most cases the package name is already used as the array key.
-    if (isset(static::$packageToCleanup[$package_name])) {
-      $package_key = $package_name;
-    }
-    else {
-      // Handle any mismatch in case between the package name and array key.
-      // For example, the array key 'mikey179/vfsStream' needs to be found
-      // when composer returns a package name of 'mikey179/vfsstream'.
-      foreach (static::$packageToCleanup as $key => $dirs) {
-        if (strtolower($key) === $package_name) {
-          $package_key = $key;
-          break;
-        }
-      }
+      $io->write('<comment>' . $message . '</comment>');
     }
-    return $package_key;
   }
 
   /**
@@ -276,32 +156,4 @@ protected static function findPackageKey($package_name) {
   public static function removeTimeout() {
     ProcessExecutor::setTimeout(0);
   }
-
-  /**
-   * Helper method to remove directories and the files they contain.
-   *
-   * @param string $path
-   *   The directory or file to remove. It must exist.
-   *
-   * @return bool
-   *   TRUE on success or FALSE on failure.
-   */
-  protected static function deleteRecursive($path) {
-    if (is_file($path) || is_link($path)) {
-      return unlink($path);
-    }
-    $success = TRUE;
-    $dir = dir($path);
-    while (($entry = $dir->read()) !== FALSE) {
-      if ($entry == '.' || $entry == '..') {
-        continue;
-      }
-      $entry_path = $path . '/' . $entry;
-      $success = static::deleteRecursive($entry_path) && $success;
-    }
-    $dir->close();
-
-    return rmdir($path) && $success;
-  }
-
 }
diff --git a/core/tests/Drupal/Tests/Component/Scaffold/FetcherTest.php b/core/tests/Drupal/Tests/Component/Scaffold/FetcherTest.php
new file mode 100644
index 0000000000..48f341a6c1
--- /dev/null
+++ b/core/tests/Drupal/Tests/Component/Scaffold/FetcherTest.php
@@ -0,0 +1,85 @@
+<?php
+
+namespace Drupal\Tests\Component\Scaffold;
+
+use Composer\IO\NullIO;
+use Composer\Util\Filesystem;
+use Composer\Util\RemoteFilesystem;
+use Drupal\Component\Scaffold\FileFetcher;
+use PHPUnit\Framework\TestCase;
+/**
+ * Unit tests for the Scaffold FileFetcher.
+ *
+ * @see \Drupal\Component\Scaffold\FileFetcher.
+ *
+ * @group Scaffold
+ */
+class FetcherTest extends TestCase {
+
+  /**
+   * @var \Composer\Util\Filesystem
+   */
+  protected $fs;
+
+  /**
+   * @var string
+   */
+  protected $tmpDir;
+
+  /**
+   * @var string
+   */
+  protected $rootDir;
+
+  /**
+   * @var string
+   */
+  protected $tmpReleaseTag;
+
+  /**
+   * SetUp test.
+   */
+  public function setUp() {
+    $this->rootDir = realpath(realpath(__DIR__ . '/Scaffold'));
+
+    // Prepare temp directory.
+    $this->fs = new Filesystem();
+    $this->tmpDir = realpath(sys_get_temp_dir()) . DIRECTORY_SEPARATOR . 'drupal-scaffold';
+    $this->ensureDirectoryExistsAndClear($this->tmpDir);
+
+    chdir($this->tmpDir);
+  }
+
+  /**
+   * Makes sure the given directory exists and has no content.
+   *
+   * @param string $directory
+   */
+  protected function ensureDirectoryExistsAndClear($directory) {
+    if (is_dir($directory)) {
+      $this->fs->removeDirectory($directory);
+    }
+    mkdir($directory, 0777, TRUE);
+  }
+
+  public function testFetch() {
+    $fetcher = new FileFetcher(new RemoteFilesystem(new NullIO()), 'https://cgit.drupalcode.org/drupal/plain/{path}?h={version}', new NullIO());
+    $fetcher->setFilenames([
+      '.htaccess' => '.htaccess',
+      'sites/default/default.settings.php' => 'sites/default/default.settings.php',
+    ]);
+    $fetcher->fetch('8.1.1', $this->tmpDir, TRUE);
+    $this->assertFileExists($this->tmpDir . '/.htaccess');
+    $this->assertFileExists($this->tmpDir . '/sites/default/default.settings.php');
+  }
+
+  public function testInitialFetch() {
+    $fetcher = new FileFetcher(new RemoteFilesystem(new NullIO()), 'https://cgit.drupalcode.org/drupal/plain/{path}?h={version}', new NullIO());
+    $fetcher->setFilenames([
+      'sites/default/default.settings.php' => 'sites/default/settings.php',
+    ]);
+    $fetcher->fetch('8.1.1', $this->tmpDir, FALSE);
+    $this->assertFileExists($this->tmpDir . '/sites/default/settings.php');
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php b/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php
new file mode 100644
index 0000000000..92c4338edd
--- /dev/null
+++ b/core/tests/Drupal/Tests/Component/Scaffold/PluginTest.php
@@ -0,0 +1,174 @@
+<?php
+
+namespace Drupal\Tests\Component\Scaffold;
+
+use Composer\Util\Filesystem;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Process\Process;
+
+/**
+ * Tests composer plugin functionality.
+ *
+ * @see \Drupal\Component\Scaffold\Plugin.
+ *
+ * @group Scaffold
+ */
+class PluginTest extends TestCase {
+
+  /**
+   * Filesystem object.
+   *
+   * @var \Composer\Util\Filesystem
+   */
+  protected $fs;
+
+  /**
+   * Temp directory where we'll exercise the plugin.
+   *
+   * @var string
+   */
+  protected $tmpDir;
+
+  /**
+   * The root directory of the component within the Drupal codebase.
+   *
+   * @var string
+   */
+  protected $componentRootDir;
+
+  /**
+   * The root directory of our Drupal codebase.
+   *
+   * @var string
+   */
+  protected $drupalRootDir;
+
+  /**
+   * SetUp test.
+   */
+  public function setUp() {
+    // @todo: Change this to be the component root dir when we start testing
+    //        components in isolation.
+    //        https://www.drupal.org/project/drupal/issues/2943856
+    $this->drupalRootDir = dirname(dirname(dirname(dirname(dirname(dirname(__DIR__))))));
+    // Get the root directory of the Scaffold component.
+    $this->componentRootDir = $this->drupalRootDir . '/core/lib/Drupal/Component/Scaffold';
+
+    // Prepare temp directory.
+    $this->fs = new Filesystem();
+    $this->tmpDir = realpath(sys_get_temp_dir()) . DIRECTORY_SEPARATOR . 'drupal-scaffold';
+    $this->ensureDirectoryExistsAndClear($this->tmpDir);
+    $this->writeComposerJSON();
+
+    chdir($this->tmpDir);
+  }
+
+  /**
+   * TearDown.
+   *
+   * @return void
+   */
+  public function tearDown() {
+    $this->fs->removeDirectory($this->tmpDir);
+  }
+
+  /**
+   * Tests a simple composer install without core, but adding core later.
+   */
+  public function testComposerInstallAndUpdate() {
+    $exampleScaffoldFile = $this->tmpDir . DIRECTORY_SEPARATOR . 'index.php';
+
+    $this->assertFileNotExists($exampleScaffoldFile, 'Scaffold file should not be exist.');
+    $this->composer('install --no-dev --prefer-dist');
+    $this->assertFileExists($this->tmpDir . DIRECTORY_SEPARATOR . 'core', 'Drupal core is installed.');
+    $this->assertFileExists($exampleScaffoldFile, 'Scaffold file should be automatically installed.');
+
+    $this->fs->remove($exampleScaffoldFile);
+    $this->assertFileNotExists($exampleScaffoldFile, 'Scaffold file should not exist.');
+    $this->composer('drupal:scaffold');
+    $this->assertFileExists($exampleScaffoldFile, 'Scaffold file should be installed by "drupal:scaffold" command.');
+
+    // We touch a scaffold file, so we can check the file was modified after the
+    // scaffold update.
+    $version = '8.7.x-dev';
+    touch($exampleScaffoldFile);
+    $mtime_touched = filemtime($exampleScaffoldFile);
+    // Requiring a newer version triggers "composer update".
+    $this->composer('require --update-with-dependencies --prefer-dist --update-no-dev drupal/core:"' . $version . '"');
+    clearstatcache();
+    $mtime_after = filemtime($exampleScaffoldFile);
+    $this->assertNotEquals($mtime_after, $mtime_touched, 'Scaffold file was modified by composer update. (' . $version . ')');
+
+    // We touch a scaffold file, so we can check the file was modified by the
+    // custom command.
+    file_put_contents($exampleScaffoldFile, 1);
+    $this->composer('drupal:scaffold');
+    $this->assertNotEquals(file_get_contents($exampleScaffoldFile), 1, 'Scaffold file was modified by custom command.');
+  }
+
+  /**
+   * Writes the default composer json to the temp direcoty.
+   */
+  protected function writeComposerJSON() {
+    $json = json_encode($this->composerJSONDefaults(), JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
+    // Write composer.json.
+    file_put_contents($this->tmpDir . '/composer.json', $json);
+  }
+
+  /**
+   * Provides the default composer.json data.
+   *
+   * @return array
+   */
+  protected function composerJSONDefaults() {
+    $package = json_decode(file_get_contents($this->componentRootDir . '/composer.json'), TRUE);
+    $package['dist'] = [
+      'type' => 'path',
+      'url' => $this->componentRootDir,
+    ];
+    $package['version'] = '999.0.' . time();
+    return [
+      'repositories' => [
+        [
+          'type' => 'package',
+          'package' => $package,
+        ],
+      ],
+      'require' => [
+        'composer/installers' => '^1.0.20',
+        'drupal/drupal-scaffold' => $package['version'],
+        'drupal/core' => '8.6.0',
+      ],
+      'minimum-stability' => 'dev',
+      'prefer-stable' => TRUE,
+    ];
+  }
+
+  /**
+   * Wrapper for the composer command.
+   *
+   * @param string $command
+   *   Composer command name, arguments and/or options.
+   */
+  protected function composer($command) {
+    $commands = [
+      $this->drupalRootDir . '/vendor/bin/composer',
+      $command,
+    ];
+    $ps = new Process(implode(' ', $commands), $this->tmpDir);
+    $ps->mustRun();
+  }
+
+  /**
+   * Makes sure the given directory exists and has no content.
+   *
+   * @param string $directory
+   */
+  protected function ensureDirectoryExistsAndClear($directory) {
+    if (is_dir($directory)) {
+      $this->fs->removeDirectory($directory);
+    }
+    mkdir($directory, 0777, TRUE);
+  }
+
+}