From 344d8422e388c11a38bdf01060f5acf3670cb4f2 Mon Sep 17 00:00:00 2001
From: Lee Rowlands <lee.rowlands@previousnext.com.au>
Date: Tue, 6 Aug 2019 15:51:39 +1000
Subject: [PATCH] Issue #2912387 by greg.1.anderson, Mile23, Mixologic,
 larowlan, jibran, alexpott, catch: Stop using wikimedia/composer-merge-plugin

---
 composer.json                                 |  29 +-
 composer.lock                                 | 303 ++++++++++++++----
 core/composer.json                            |  50 ---
 core/lib/Drupal/Core/Composer/Composer.php    |  13 +
 .../Drupal/Nightwatch/nightwatch.conf.js      |   7 +-
 .../Tests/Core/Composer/ComposerTest.php      |  28 ++
 6 files changed, 313 insertions(+), 117 deletions(-)
 create mode 100644 core/tests/Drupal/Tests/Core/Composer/ComposerTest.php

diff --git a/composer.json b/composer.json
index 8612c77ac221..7b00ebb866a3 100644
--- a/composer.json
+++ b/composer.json
@@ -5,10 +5,24 @@
     "license": "GPL-2.0-or-later",
     "require": {
         "composer/installers": "^1.0.24",
-        "wikimedia/composer-merge-plugin": "^1.4"
+        "wikimedia/composer-merge-plugin": "^1.4",
+        "drupal/core": "self.version"
     },
-    "replace": {
-        "drupal/core": "^8.8"
+    "require-dev": {
+        "behat/mink": "1.7.x-dev",
+        "behat/mink-goutte-driver": "^1.2",
+        "behat/mink-selenium2-driver": "1.3.x-dev",
+        "composer/composer": "^1.8",
+        "drupal/coder": "^8.3.2",
+        "jcalderonzumba/gastonjs": "^1.0.2",
+        "jcalderonzumba/mink-phantomjs-driver": "^0.3.1",
+        "mikey179/vfsstream": "^1.2",
+        "phpunit/phpunit": "^6.5",
+        "phpspec/prophecy": "^1.7",
+        "symfony/css-selector": "^3.4.0",
+        "symfony/phpunit-bridge": "^3.4.3",
+        "symfony/debug": "^3.4.0",
+        "justinrainbow/json-schema": "^5.2"
     },
     "minimum-stability": "dev",
     "prefer-stable": true,
@@ -25,9 +39,6 @@
             "https://www.drupal.org/node/2718229"
         ],
         "merge-plugin": {
-            "include": [
-                "core/composer.json"
-            ],
             "recurse": true,
             "replace": false,
             "merge-extra": false
@@ -48,6 +59,8 @@
         }
     },
     "scripts": {
+        "pre-install-cmd": "Drupal\\Core\\Composer\\Composer::ensureComposerVersion",
+        "pre-update-cmd": "Drupal\\Core\\Composer\\Composer::ensureComposerVersion",
         "pre-autoload-dump": "Drupal\\Core\\Composer\\Composer::preAutoloadDump",
         "post-autoload-dump": "Drupal\\Core\\Composer\\Composer::ensureHtaccess",
         "post-package-install": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
@@ -59,6 +72,10 @@
         {
             "type": "composer",
             "url": "https://packages.drupal.org/8"
+        },
+        {
+            "type": "path",
+            "url": "core"
         }
     ]
 }
diff --git a/composer.lock b/composer.lock
index c43e82677e31..775324f2471f 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": "15aa825e18c7099ad637f9d55109db29",
+    "content-hash": "36ce6886f9438a31a1d93784286214df",
     "packages": [
         {
             "name": "asm89/stack-cors",
@@ -674,6 +674,204 @@
             ],
             "time": "2014-09-09T13:34:57+00:00"
         },
+        {
+            "name": "drupal/core",
+            "version": "8.8.x-dev",
+            "dist": {
+                "type": "path",
+                "url": "core",
+                "reference": "27f439f6978708d477ebb70f2ce97b28e8043da2"
+            },
+            "require": {
+                "asm89/stack-cors": "^1.1",
+                "composer/semver": "^1.0",
+                "doctrine/annotations": "^1.2",
+                "doctrine/common": "^2.5",
+                "easyrdf/easyrdf": "^0.9",
+                "egulias/email-validator": "^2.0",
+                "ext-date": "*",
+                "ext-dom": "*",
+                "ext-filter": "*",
+                "ext-gd": "*",
+                "ext-hash": "*",
+                "ext-json": "*",
+                "ext-pcre": "*",
+                "ext-pdo": "*",
+                "ext-session": "*",
+                "ext-simplexml": "*",
+                "ext-spl": "*",
+                "ext-tokenizer": "*",
+                "ext-xml": "*",
+                "guzzlehttp/guzzle": "^6.2.1",
+                "masterminds/html5": "^2.1",
+                "pear/archive_tar": "^1.4",
+                "php": ">=7.0.8",
+                "stack/builder": "^1.0",
+                "symfony-cmf/routing": "^1.4",
+                "symfony/class-loader": "~3.4.0",
+                "symfony/console": "~3.4.0",
+                "symfony/dependency-injection": "~3.4.26",
+                "symfony/event-dispatcher": "~3.4.0",
+                "symfony/http-foundation": "~3.4.27",
+                "symfony/http-kernel": "~3.4.14",
+                "symfony/polyfill-iconv": "^1.0",
+                "symfony/process": "~3.4.0",
+                "symfony/psr-http-message-bridge": "^1.0",
+                "symfony/routing": "~3.4.0",
+                "symfony/serializer": "~3.4.0",
+                "symfony/translation": "~3.4.0",
+                "symfony/validator": "~3.4.0",
+                "symfony/yaml": "~3.4.5",
+                "twig/twig": "^1.38.2",
+                "typo3/phar-stream-wrapper": "^2.1.1",
+                "zendframework/zend-diactoros": "^1.1",
+                "zendframework/zend-feed": "^2.4"
+            },
+            "conflict": {
+                "drush/drush": "<8.1.10"
+            },
+            "replace": {
+                "drupal/action": "self.version",
+                "drupal/aggregator": "self.version",
+                "drupal/automated_cron": "self.version",
+                "drupal/ban": "self.version",
+                "drupal/bartik": "self.version",
+                "drupal/basic_auth": "self.version",
+                "drupal/big_pipe": "self.version",
+                "drupal/block": "self.version",
+                "drupal/block_content": "self.version",
+                "drupal/block_place": "self.version",
+                "drupal/book": "self.version",
+                "drupal/breakpoint": "self.version",
+                "drupal/ckeditor": "self.version",
+                "drupal/classy": "self.version",
+                "drupal/color": "self.version",
+                "drupal/comment": "self.version",
+                "drupal/config": "self.version",
+                "drupal/config_environment": "self.version",
+                "drupal/config_translation": "self.version",
+                "drupal/contact": "self.version",
+                "drupal/content_moderation": "self.version",
+                "drupal/content_translation": "self.version",
+                "drupal/contextual": "self.version",
+                "drupal/core-annotation": "self.version",
+                "drupal/core-assertion": "self.version",
+                "drupal/core-bridge": "self.version",
+                "drupal/core-class-finder": "self.version",
+                "drupal/core-datetime": "self.version",
+                "drupal/core-dependency-injection": "self.version",
+                "drupal/core-diff": "self.version",
+                "drupal/core-discovery": "self.version",
+                "drupal/core-event-dispatcher": "self.version",
+                "drupal/core-file-cache": "self.version",
+                "drupal/core-filesystem": "self.version",
+                "drupal/core-gettext": "self.version",
+                "drupal/core-graph": "self.version",
+                "drupal/core-http-foundation": "self.version",
+                "drupal/core-php-storage": "self.version",
+                "drupal/core-plugin": "self.version",
+                "drupal/core-proxy-builder": "self.version",
+                "drupal/core-render": "self.version",
+                "drupal/core-serialization": "self.version",
+                "drupal/core-transliteration": "self.version",
+                "drupal/core-utility": "self.version",
+                "drupal/core-uuid": "self.version",
+                "drupal/core-version": "self.version",
+                "drupal/datetime": "self.version",
+                "drupal/datetime_range": "self.version",
+                "drupal/dblog": "self.version",
+                "drupal/dynamic_page_cache": "self.version",
+                "drupal/editor": "self.version",
+                "drupal/entity_reference": "self.version",
+                "drupal/field": "self.version",
+                "drupal/field_layout": "self.version",
+                "drupal/field_ui": "self.version",
+                "drupal/file": "self.version",
+                "drupal/filter": "self.version",
+                "drupal/forum": "self.version",
+                "drupal/hal": "self.version",
+                "drupal/help": "self.version",
+                "drupal/help_topics": "self.version",
+                "drupal/history": "self.version",
+                "drupal/image": "self.version",
+                "drupal/inline_form_errors": "self.version",
+                "drupal/jsonapi": "self.version",
+                "drupal/language": "self.version",
+                "drupal/layout_builder": "self.version",
+                "drupal/layout_discovery": "self.version",
+                "drupal/link": "self.version",
+                "drupal/locale": "self.version",
+                "drupal/media": "self.version",
+                "drupal/media_library": "self.version",
+                "drupal/menu_link_content": "self.version",
+                "drupal/menu_ui": "self.version",
+                "drupal/migrate": "self.version",
+                "drupal/migrate_drupal": "self.version",
+                "drupal/migrate_drupal_multilingual": "self.version",
+                "drupal/migrate_drupal_ui": "self.version",
+                "drupal/minimal": "self.version",
+                "drupal/node": "self.version",
+                "drupal/options": "self.version",
+                "drupal/page_cache": "self.version",
+                "drupal/path": "self.version",
+                "drupal/quickedit": "self.version",
+                "drupal/rdf": "self.version",
+                "drupal/responsive_image": "self.version",
+                "drupal/rest": "self.version",
+                "drupal/search": "self.version",
+                "drupal/serialization": "self.version",
+                "drupal/settings_tray": "self.version",
+                "drupal/seven": "self.version",
+                "drupal/shortcut": "self.version",
+                "drupal/simpletest": "self.version",
+                "drupal/standard": "self.version",
+                "drupal/stark": "self.version",
+                "drupal/statistics": "self.version",
+                "drupal/syslog": "self.version",
+                "drupal/system": "self.version",
+                "drupal/taxonomy": "self.version",
+                "drupal/telephone": "self.version",
+                "drupal/text": "self.version",
+                "drupal/toolbar": "self.version",
+                "drupal/tour": "self.version",
+                "drupal/tracker": "self.version",
+                "drupal/update": "self.version",
+                "drupal/user": "self.version",
+                "drupal/views": "self.version",
+                "drupal/views_ui": "self.version",
+                "drupal/workflows": "self.version",
+                "drupal/workspaces": "self.version"
+            },
+            "type": "drupal-core",
+            "autoload": {
+                "psr-4": {
+                    "Drupal\\Core\\": "lib/Drupal/Core",
+                    "Drupal\\Component\\": "lib/Drupal/Component",
+                    "Drupal\\Driver\\": "../drivers/lib/Drupal/Driver"
+                },
+                "classmap": [
+                    "lib/Drupal.php",
+                    "lib/Drupal/Component/Utility/Timer.php",
+                    "lib/Drupal/Component/Utility/Unicode.php",
+                    "lib/Drupal/Core/Database/Database.php",
+                    "lib/Drupal/Core/DrupalKernel.php",
+                    "lib/Drupal/Core/DrupalKernelInterface.php",
+                    "lib/Drupal/Core/Site/Settings.php"
+                ]
+            },
+            "scripts": {
+                "pre-autoload-dump": [
+                    "Drupal\\Core\\Composer\\Composer::preAutoloadDump"
+                ],
+                "post-autoload-dump": [
+                    "Drupal\\Core\\Composer\\Composer::ensureHtaccess"
+                ]
+            },
+            "license": [
+                "GPL-2.0-or-later"
+            ],
+            "description": "Drupal is an open source content management platform powering millions of websites and applications."
+        },
         {
             "name": "easyrdf/easyrdf",
             "version": "0.9.1",
@@ -714,14 +912,14 @@
             "authors": [
                 {
                     "name": "Nicholas Humfrey",
+                    "role": "Developer",
                     "email": "njh@aelius.com",
-                    "homepage": "http://www.aelius.com/njh/",
-                    "role": "Developer"
+                    "homepage": "http://www.aelius.com/njh/"
                 },
                 {
                     "name": "Alexey Zakhlestin",
-                    "email": "indeyets@gmail.com",
-                    "role": "Developer"
+                    "role": "Developer",
+                    "email": "indeyets@gmail.com"
                 }
             ],
             "description": "EasyRdf is a PHP library designed to make it easy to consume and produce RDF.",
@@ -2775,19 +2973,19 @@
             "authors": [
                 {
                     "name": "Fabien Potencier",
+                    "role": "Lead Developer",
                     "email": "fabien@symfony.com",
-                    "homepage": "http://fabien.potencier.org",
-                    "role": "Lead Developer"
+                    "homepage": "http://fabien.potencier.org"
                 },
                 {
                     "name": "Armin Ronacher",
-                    "email": "armin.ronacher@active-4.com",
-                    "role": "Project Founder"
+                    "role": "Project Founder",
+                    "email": "armin.ronacher@active-4.com"
                 },
                 {
                     "name": "Twig Team",
-                    "homepage": "https://twig.symfony.com/contributors",
-                    "role": "Contributors"
+                    "role": "Contributors",
+                    "homepage": "https://twig.symfony.com/contributors"
                 }
             ],
             "description": "Twig, the flexible, fast, and secure template language for PHP",
@@ -3102,26 +3300,27 @@
             "source": {
                 "type": "git",
                 "url": "https://github.com/minkphp/Mink.git",
-                "reference": "9ea1cebe3dc529ba3861d87c818f045362c40484"
+                "reference": "a534fe7dac9525e8e10ca68e737c3d7e5058ec83"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/minkphp/Mink/zipball/9ea1cebe3dc529ba3861d87c818f045362c40484",
-                "reference": "9ea1cebe3dc529ba3861d87c818f045362c40484",
+                "url": "https://api.github.com/repos/minkphp/Mink/zipball/a534fe7dac9525e8e10ca68e737c3d7e5058ec83",
+                "reference": "a534fe7dac9525e8e10ca68e737c3d7e5058ec83",
                 "shasum": ""
             },
             "require": {
                 "php": ">=5.3.1",
-                "symfony/css-selector": "~2.1|~3.0"
+                "symfony/css-selector": "^2.7|^3.0|^4.0"
             },
             "require-dev": {
-                "symfony/phpunit-bridge": "~2.7|~3.0"
+                "symfony/phpunit-bridge": "^4.2"
             },
             "suggest": {
                 "behat/mink-browserkit-driver": "extremely fast headless driver for Symfony\\Kernel-based apps (Sf2, Silex)",
                 "behat/mink-goutte-driver": "fast headless driver for any app without JS emulation",
                 "behat/mink-selenium2-driver": "slow, but JS-enabled driver for any app (requires Selenium2)",
-                "behat/mink-zombie-driver": "fast and JS-enabled headless driver for any app (requires node.js)"
+                "behat/mink-zombie-driver": "fast and JS-enabled headless driver for any app (requires node.js)",
+                "dmore/chrome-mink-driver": "fast and JS-enabled driver for any app (requires chromium or google chrome)"
             },
             "type": "library",
             "extra": {
@@ -3152,7 +3351,7 @@
                 "testing",
                 "web"
             ],
-            "time": "2017-02-06T09:59:54+00:00"
+            "time": "2019-07-15T12:45:29+00:00"
         },
         {
             "name": "behat/mink-browserkit-driver",
@@ -3271,12 +3470,12 @@
             "source": {
                 "type": "git",
                 "url": "https://github.com/minkphp/MinkSelenium2Driver.git",
-                "reference": "93474c65a2a7bf959200ab5f7a14cc450645c185"
+                "reference": "8684ee4e634db7abda9039ea53545f86fc1e105a"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/minkphp/MinkSelenium2Driver/zipball/93474c65a2a7bf959200ab5f7a14cc450645c185",
-                "reference": "93474c65a2a7bf959200ab5f7a14cc450645c185",
+                "url": "https://api.github.com/repos/minkphp/MinkSelenium2Driver/zipball/8684ee4e634db7abda9039ea53545f86fc1e105a",
+                "reference": "8684ee4e634db7abda9039ea53545f86fc1e105a",
                 "shasum": ""
             },
             "require": {
@@ -3324,7 +3523,7 @@
                 "testing",
                 "webdriver"
             ],
-            "time": "2018-01-07T19:17:08+00:00"
+            "time": "2018-10-10T12:39:06+00:00"
         },
         {
             "name": "composer/ca-bundle",
@@ -3995,7 +4194,7 @@
             "time": "2019-01-14T23:55:14+00:00"
         },
         {
-            "name": "mikey179/vfsStream",
+            "name": "mikey179/vfsstream",
             "version": "v1.6.5",
             "source": {
                 "type": "git",
@@ -4032,8 +4231,8 @@
             "authors": [
                 {
                     "name": "Frank Kleine",
-                    "homepage": "http://frankkleine.de/",
-                    "role": "Developer"
+                    "role": "Developer",
+                    "homepage": "http://frankkleine.de/"
                 }
             ],
             "description": "Virtual file system to mock the real file system in unit tests.",
@@ -4170,18 +4369,18 @@
             "authors": [
                 {
                     "name": "Arne Blankerts",
-                    "email": "arne@blankerts.de",
-                    "role": "Developer"
+                    "role": "Developer",
+                    "email": "arne@blankerts.de"
                 },
                 {
                     "name": "Sebastian Heuer",
-                    "email": "sebastian@phpeople.de",
-                    "role": "Developer"
+                    "role": "Developer",
+                    "email": "sebastian@phpeople.de"
                 },
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sebastian@phpunit.de",
-                    "role": "Developer"
+                    "role": "Developer",
+                    "email": "sebastian@phpunit.de"
                 }
             ],
             "description": "Library for handling version information and constraints",
@@ -4349,8 +4548,8 @@
             "authors": [
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sebastian@phpunit.de",
-                    "role": "lead"
+                    "role": "lead",
+                    "email": "sebastian@phpunit.de"
                 }
             ],
             "description": "Library that provides collection, processing, and rendering functionality for PHP code coverage information.",
@@ -4397,8 +4596,8 @@
             "authors": [
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sb@sebastian-bergmann.de",
-                    "role": "lead"
+                    "role": "lead",
+                    "email": "sb@sebastian-bergmann.de"
                 }
             ],
             "description": "FilterIterator implementation that filters files based on a list of suffixes.",
@@ -4439,8 +4638,8 @@
             "authors": [
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sebastian@phpunit.de",
-                    "role": "lead"
+                    "role": "lead",
+                    "email": "sebastian@phpunit.de"
                 }
             ],
             "description": "Simple template engine.",
@@ -4488,8 +4687,8 @@
             "authors": [
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sb@sebastian-bergmann.de",
-                    "role": "lead"
+                    "role": "lead",
+                    "email": "sb@sebastian-bergmann.de"
                 }
             ],
             "description": "Utility class for timing",
@@ -4619,8 +4818,8 @@
             "authors": [
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sebastian@phpunit.de",
-                    "role": "lead"
+                    "role": "lead",
+                    "email": "sebastian@phpunit.de"
                 }
             ],
             "description": "The PHP Unit Testing framework.",
@@ -5243,8 +5442,8 @@
             "authors": [
                 {
                     "name": "Sebastian Bergmann",
-                    "email": "sebastian@phpunit.de",
-                    "role": "lead"
+                    "role": "lead",
+                    "email": "sebastian@phpunit.de"
                 }
             ],
             "description": "Library that helps with managing the version number of Git-hosted PHP projects",
@@ -5770,26 +5969,12 @@
     "aliases": [],
     "minimum-stability": "dev",
     "stability-flags": {
+        "drupal/core": 20,
         "behat/mink": 20,
         "behat/mink-selenium2-driver": 20
     },
     "prefer-stable": true,
     "prefer-lowest": false,
-    "platform": {
-        "ext-date": "*",
-        "ext-dom": "*",
-        "ext-filter": "*",
-        "ext-gd": "*",
-        "ext-hash": "*",
-        "ext-json": "*",
-        "ext-pcre": "*",
-        "ext-pdo": "*",
-        "ext-session": "*",
-        "ext-simplexml": "*",
-        "ext-spl": "*",
-        "ext-tokenizer": "*",
-        "ext-xml": "*",
-        "php": ">=7.0.8"
-    },
+    "platform": [],
     "platform-dev": []
 }
diff --git a/core/composer.json b/core/composer.json
index 4fee977c236e..5d248a188e6a 100644
--- a/core/composer.json
+++ b/core/composer.json
@@ -51,22 +51,6 @@
     "conflict": {
         "drush/drush": "<8.1.10"
     },
-    "require-dev": {
-        "behat/mink": "1.7.x-dev",
-        "behat/mink-goutte-driver": "^1.2",
-        "behat/mink-selenium2-driver": "1.3.x-dev",
-        "composer/composer": "^1.8",
-        "drupal/coder": "^8.3.2",
-        "jcalderonzumba/gastonjs": "^1.0.2",
-        "jcalderonzumba/mink-phantomjs-driver": "^0.3.1",
-        "mikey179/vfsstream": "^1.2",
-        "phpunit/phpunit": "^6.5",
-        "phpspec/prophecy": "^1.7",
-        "symfony/css-selector": "^3.4.0",
-        "symfony/phpunit-bridge": "^3.4.3",
-        "symfony/debug": "^3.4.0",
-        "justinrainbow/json-schema": "^5.2"
-    },
     "replace": {
         "drupal/action": "self.version",
         "drupal/aggregator": "self.version",
@@ -110,7 +94,6 @@
         "drupal/core-proxy-builder": "self.version",
         "drupal/core-render": "self.version",
         "drupal/core-serialization": "self.version",
-        "drupal/core-composer-scaffold": "self.version",
         "drupal/core-transliteration": "self.version",
         "drupal/core-utility": "self.version",
         "drupal/core-uuid": "self.version",
@@ -180,39 +163,6 @@
         "drupal/workflows": "self.version",
         "drupal/workspaces": "self.version"
     },
-    "extra": {
-        "merge-plugin": {
-            "require": [
-                "core/lib/Drupal/Component/Annotation/composer.json",
-                "core/lib/Drupal/Component/Assertion/composer.json",
-                "core/lib/Drupal/Component/Bridge/composer.json",
-                "core/lib/Drupal/Component/ClassFinder/composer.json",
-                "core/lib/Drupal/Component/Datetime/composer.json",
-                "core/lib/Drupal/Component/DependencyInjection/composer.json",
-                "core/lib/Drupal/Component/Diff/composer.json",
-                "core/lib/Drupal/Component/Discovery/composer.json",
-                "core/lib/Drupal/Component/EventDispatcher/composer.json",
-                "core/lib/Drupal/Component/FileCache/composer.json",
-                "core/lib/Drupal/Component/FileSystem/composer.json",
-                "core/lib/Drupal/Component/Gettext/composer.json",
-                "core/lib/Drupal/Component/Graph/composer.json",
-                "core/lib/Drupal/Component/HttpFoundation/composer.json",
-                "core/lib/Drupal/Component/PhpStorage/composer.json",
-                "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/Serialization/composer.json",
-                "core/lib/Drupal/Component/Scaffold/composer.json",
-                "core/lib/Drupal/Component/Transliteration/composer.json",
-                "core/lib/Drupal/Component/Utility/composer.json",
-                "core/lib/Drupal/Component/Uuid/composer.json",
-                "core/lib/Drupal/Component/Version/composer.json"
-            ],
-            "recurse": false,
-            "replace": false,
-            "merge-extra": false
-        }
-    },
     "minimum-stability": "dev",
     "prefer-stable": true,
     "autoload": {
diff --git a/core/lib/Drupal/Core/Composer/Composer.php b/core/lib/Drupal/Core/Composer/Composer.php
index 7be3ca4d44db..cae919645002 100644
--- a/core/lib/Drupal/Core/Composer/Composer.php
+++ b/core/lib/Drupal/Core/Composer/Composer.php
@@ -3,6 +3,8 @@
 namespace Drupal\Core\Composer;
 
 use Drupal\Component\PhpStorage\FileStorage;
+use Composer\Semver\Comparator;
+use Composer\Composer as ComposerApp;
 use Composer\Script\Event;
 use Composer\Installer\PackageEvent;
 use Composer\Semver\Constraint\Constraint;
@@ -94,6 +96,17 @@ class Composer {
     'zendframework/zend-stdlib' => ['doc'],
   ];
 
+  /**
+   * Ensure that the minimum required version of Composer is running.
+   * Throw an exception if Composer is too old.
+   */
+  public static function ensureComposerVersion() {
+    $composerVersion = ComposerApp::getVersion();
+    if (Comparator::lessThan($composerVersion, '1.9.0')) {
+      throw new \RuntimeException("Drupal core development requires Composer 1.9.0, but Composer $composerVersion is installed. Please run 'composer self-update'.");
+    }
+  }
+
   /**
    * Add vendor classes to Composer's static classmap.
    */
diff --git a/core/tests/Drupal/Nightwatch/nightwatch.conf.js b/core/tests/Drupal/Nightwatch/nightwatch.conf.js
index 7f4cb83529b8..ee98b2815f3c 100644
--- a/core/tests/Drupal/Nightwatch/nightwatch.conf.js
+++ b/core/tests/Drupal/Nightwatch/nightwatch.conf.js
@@ -10,13 +10,16 @@ const collectedFolders = {
   Pages: [],
 };
 const searchDirectory = process.env.DRUPAL_NIGHTWATCH_SEARCH_DIRECTORY || '';
+const defaultIgnore = ['vendor/**'];
 
 glob
   .sync('**/tests/**/Nightwatch/**/*.js', {
     cwd: path.resolve(process.cwd(), `../${searchDirectory}`),
     ignore: process.env.DRUPAL_NIGHTWATCH_IGNORE_DIRECTORIES
-      ? process.env.DRUPAL_NIGHTWATCH_IGNORE_DIRECTORIES.split(',')
-      : [],
+      ? process.env.DRUPAL_NIGHTWATCH_IGNORE_DIRECTORIES.split(',').concat(
+          defaultIgnore,
+        )
+      : defaultIgnore,
   })
   .forEach(file => {
     let m = regex.exec(file);
diff --git a/core/tests/Drupal/Tests/Core/Composer/ComposerTest.php b/core/tests/Drupal/Tests/Core/Composer/ComposerTest.php
new file mode 100644
index 000000000000..906b45d4e525
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Composer/ComposerTest.php
@@ -0,0 +1,28 @@
+<?php
+
+namespace Drupal\Tests\Core\Composer;
+
+use Drupal\Core\Composer\Composer;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Composer\Composer
+ * @group Composer
+ */
+class ComposerTest extends UnitTestCase {
+
+  /**
+   * Verify that Composer::ensureComposerVersion() doesn't break.
+   *
+   * @covers::ensureComposerVersion
+   */
+  public function testEnsureComposerVersion() {
+    try {
+      $this->assertNull(Composer::ensureComposerVersion());
+    }
+    catch (\RuntimeException $e) {
+      $this->assertRegExp('/Drupal core development requires Composer 1.9.0, but Composer /', $e->getMessage());
+    }
+  }
+
+}
-- 
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