From 661b7cc6675a0191f0f5fec8c93491893da18a19 Mon Sep 17 00:00:00 2001
From: Alex Pott <alex.a.pott@googlemail.com>
Date: Thu, 31 Oct 2019 17:54:58 +0100
Subject: [PATCH] Revert "Revert "Issue #3087482 by Mile23, greg.1.anderson,
 AaronMcHale, johndevman, mbaynton, alexpott: Add 'next steps' info to
 Composer installation output""

This reverts commit 32b0bacf94b6dcc7a87b2bbcad3b346f092825cd.
---
 composer.json                                 |  22 ++
 composer.lock                                 |  33 +-
 composer/Plugin/ProjectMessage/LICENSE.txt    | 339 ++++++++++++++++++
 composer/Plugin/ProjectMessage/Message.php    | 112 ++++++
 .../Plugin/ProjectMessage/MessagePlugin.php   |  63 ++++
 composer/Plugin/ProjectMessage/README.md      | 101 ++++++
 composer/Plugin/ProjectMessage/TESTING.txt    |  18 +
 composer/Plugin/ProjectMessage/composer.json  |  20 ++
 composer/Template/LegacyProject/composer.json |  27 +-
 .../Template/RecommendedProject/composer.json |  29 +-
 .../Plugin/ProjectMessage/ConfigTest.php      | 100 ++++++
 11 files changed, 860 insertions(+), 4 deletions(-)
 create mode 100644 composer/Plugin/ProjectMessage/LICENSE.txt
 create mode 100644 composer/Plugin/ProjectMessage/Message.php
 create mode 100644 composer/Plugin/ProjectMessage/MessagePlugin.php
 create mode 100644 composer/Plugin/ProjectMessage/README.md
 create mode 100644 composer/Plugin/ProjectMessage/TESTING.txt
 create mode 100644 composer/Plugin/ProjectMessage/composer.json
 create mode 100644 core/tests/Drupal/Tests/Composer/Plugin/ProjectMessage/ConfigTest.php

diff --git a/composer.json b/composer.json
index 569097373ef9..e58254120163 100644
--- a/composer.json
+++ b/composer.json
@@ -3,9 +3,15 @@
     "description": "Drupal is an open source content management platform powering millions of websites and applications.",
     "type": "project",
     "license": "GPL-2.0-or-later",
+    "homepage": "https://www.drupal.org/project/drupal",
+    "support": {
+        "docs": "https://www.drupal.org/docs/user_guide/en/index.html",
+        "chat": "https://www.drupal.org/node/314178"
+    },
     "require": {
         "composer/installers": "^1.0.24",
         "drupal/core": "self.version",
+        "drupal/core-project-message": "self.version",
         "drupal/core-vendor-hardening": "self.version",
         "wikimedia/composer-merge-plugin": "^1.4"
     },
@@ -58,6 +64,18 @@
             "drush/Commands/contrib/{$name}": ["type:drupal-drush"],
             "modules/custom/{$name}": ["type:drupal-custom-module"],
             "themes/custom/{$name}": ["type:drupal-custom-theme"]
+        },
+        "drupal-core-project-message": {
+            "post-install-cmd-message": [
+                "<bg=blue;fg=white>drupal/drupal</>: This package is meant for core development,",
+                "               and not intended to be used for production sites.",
+                "               See: https://www.drupal.org/node/3082474"
+            ],
+            "post-create-project-cmd-message": [
+                "<bg=red;fg=white>drupal/drupal</>: This package is meant for core development,",
+                "               and not intended to be used for production sites.",
+                "               See: https://www.drupal.org/node/3082474"
+            ]
         }
     },
     "autoload": {
@@ -92,6 +110,10 @@
             "type": "path",
             "url": "core"
         },
+        {
+            "type": "path",
+            "url": "composer/Plugin/ProjectMessage"
+        },
         {
             "type": "path",
             "url": "composer/Plugin/VendorHardening"
diff --git a/composer.lock b/composer.lock
index 59e4b29c99f2..e42d57b8f581 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": "cd5ae3ea749af8e8c920008ef6c69d05",
+    "content-hash": "d95e2f200c5869caa76ca07ad911c356",
     "packages": [
         {
             "name": "asm89/stack-cors",
@@ -877,6 +877,36 @@
             ],
             "description": "Drupal is an open source content management platform powering millions of websites and applications."
         },
+        {
+            "name": "drupal/core-project-message",
+            "version": "9.0.x-dev",
+            "dist": {
+                "type": "path",
+                "url": "composer/Plugin/ProjectMessage",
+                "reference": "3b795f469441eb27854798f70cb38e717d80bbfc"
+            },
+            "require": {
+                "composer-plugin-api": "^1.1",
+                "php": ">=7.0.8"
+            },
+            "type": "composer-plugin",
+            "extra": {
+                "class": "Drupal\\Composer\\Plugin\\ProjectMessage\\MessagePlugin"
+            },
+            "autoload": {
+                "psr-4": {
+                    "Drupal\\Composer\\Plugin\\ProjectMessage\\": "."
+                }
+            },
+            "license": [
+                "GPL-2.0-or-later"
+            ],
+            "description": "Adds a message after Composer installation.",
+            "homepage": "https://www.drupal.org/project/drupal",
+            "keywords": [
+                "drupal"
+            ]
+        },
         {
             "name": "drupal/core-vendor-hardening",
             "version": "9.0.x-dev",
@@ -6705,6 +6735,7 @@
     "minimum-stability": "dev",
     "stability-flags": {
         "drupal/core": 20,
+        "drupal/core-project-message": 20,
         "drupal/core-vendor-hardening": 20,
         "behat/mink": 20,
         "behat/mink-selenium2-driver": 20
diff --git a/composer/Plugin/ProjectMessage/LICENSE.txt b/composer/Plugin/ProjectMessage/LICENSE.txt
new file mode 100644
index 000000000000..94fb84639c4b
--- /dev/null
+++ b/composer/Plugin/ProjectMessage/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/composer/Plugin/ProjectMessage/Message.php b/composer/Plugin/ProjectMessage/Message.php
new file mode 100644
index 000000000000..b0cea11b9299
--- /dev/null
+++ b/composer/Plugin/ProjectMessage/Message.php
@@ -0,0 +1,112 @@
+<?php
+
+namespace Drupal\Composer\Plugin\ProjectMessage;
+
+use Composer\Package\RootPackageInterface;
+
+/**
+ * Determine configuration.
+ */
+class Message {
+
+  /**
+   * The root package.
+   *
+   * @var \Composer\Package\RootPackageInterface
+   */
+  protected $rootPackage;
+
+  /**
+   * The name of the event.
+   *
+   * @var string
+   */
+  protected $eventName;
+
+  /**
+   * The message to display.
+   *
+   * @var string[]
+   */
+  protected $messageText = [];
+
+  /**
+   * Construct a Config object.
+   *
+   * @param \Composer\Package\RootPackageInterface $root_package
+   *   Composer package object for the root package.
+   * @param string $event_name
+   *   The event name.
+   */
+  public function __construct(RootPackageInterface $root_package, $event_name) {
+    $this->rootPackage = $root_package;
+    $this->eventName = $event_name;
+  }
+
+  public function getText() {
+    if ($this->messageText) {
+      return $this->messageText;
+    }
+    $package_config = $this->rootPackage->getExtra();
+    $file = $this->eventName . '-message.txt';
+    if ($config_file = $package_config['drupal-core-project-message'][$this->eventName . '-file'] ?? FALSE) {
+      $file = $config_file;
+    }
+
+    $message = $package_config['drupal-core-project-message'][$this->eventName . '-message'] ?? [];
+
+    if ($message) {
+      $this->messageText = $message;
+    }
+    else {
+      $this->messageText = $this->getMessageFromFile($file);
+    }
+
+    // Include structured support info from composer.json.
+    if ($config_keys = $package_config['drupal-core-project-message']['include-keys'] ?? FALSE) {
+      foreach ($config_keys as $config_key) {
+        switch ($config_key) {
+          case 'name':
+            if ($homepage = $this->rootPackage->getName()) {
+              $this->messageText[] = '  * Name: ' . $homepage;
+            }
+            break;
+          case 'description':
+            if ($homepage = $this->rootPackage->getDescription()) {
+              $this->messageText[] = '  * Description: ' . $homepage;
+            }
+            break;
+          case 'homepage':
+            if ($homepage = $this->rootPackage->getHomepage()) {
+              $this->messageText[] = '  * Homepage: ' . $homepage;
+            }
+            break;
+
+          case 'support':
+            if ($support = $this->rootPackage->getSupport()) {
+              $this->messageText[] = '  * Support:';
+              foreach ($support as $support_key => $support_value) {
+                $this->messageText[] = '    * ' . $support_key . ': ' . $support_value;
+              }
+            }
+            break;
+        }
+      }
+    }
+
+    return $this->messageText;
+  }
+
+  /**
+   * Reads the message file as an array.
+   *
+   * @param string $file
+   *   The file to read. Relative paths are relative to the project directory.
+   *
+   * @return string[]
+   */
+  protected function getMessageFromFile($file) {
+    return file_exists($file) ? file($file, FILE_IGNORE_NEW_LINES) : [];
+  }
+
+}
diff --git a/composer/Plugin/ProjectMessage/MessagePlugin.php b/composer/Plugin/ProjectMessage/MessagePlugin.php
new file mode 100644
index 000000000000..5e4f6614a521
--- /dev/null
+++ b/composer/Plugin/ProjectMessage/MessagePlugin.php
@@ -0,0 +1,63 @@
+<?php
+
+namespace Drupal\Composer\Plugin\ProjectMessage;
+
+use Composer\Composer;
+use Composer\EventDispatcher\EventSubscriberInterface;
+use Composer\IO\IOInterface;
+use Composer\Plugin\PluginInterface;
+use Composer\Script\Event;
+use Composer\Script\ScriptEvents;
+
+/**
+ * A Composer plugin to display a message after creating a project.
+ */
+class MessagePlugin implements PluginInterface, EventSubscriberInterface {
+
+  /**
+   * Composer object.
+   *
+   * @var \Composer\Composer
+   */
+  protected $composer;
+
+  /**
+   * IO object.
+   *
+   * @var \Composer\IO\IOInterface
+   */
+  protected $io;
+
+  /**
+   * Configuration.
+   *
+   * @var \Drupal\Composer\VendorHardening\Config
+   */
+  protected $config;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function activate(Composer $composer, IOInterface $io) {
+    $this->composer = $composer;
+    $this->io = $io;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      ScriptEvents::POST_CREATE_PROJECT_CMD => 'displayPostCreateMessage',
+      ScriptEvents::POST_INSTALL_CMD => 'displayPostCreateMessage',
+    ];
+  }
+
+  public function displayPostCreateMessage(Event $event) {
+    $message = new Message($this->composer->getPackage(), $event->getName());
+    if ($message = $message->getText()) {
+      $this->io->write($message);
+    }
+  }
+
+}
diff --git a/composer/Plugin/ProjectMessage/README.md b/composer/Plugin/ProjectMessage/README.md
new file mode 100644
index 000000000000..cbfc4ca7cc48
--- /dev/null
+++ b/composer/Plugin/ProjectMessage/README.md
@@ -0,0 +1,101 @@
+The Drupal Project Message Plugin
+=================================
+
+Thanks for using this Drupal component.
+
+You can participate in its development on Drupal.org, through our issue system:
+https://www.drupal.org/project/issues/drupal
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can browse the full Drupal repo here:
+http://cgit.drupalcode.org/drupal
+
+What does it do?
+----------------
+
+This Composer plugin displays a configurable message after Composer installation
+processes have finished.
+
+This is ideal for a 'next steps' type prompt to help get the user oriented.
+
+Currently only two Composer events are supported:
+- post-create-project-cmd, when a `composer create-project` command has
+  finished.
+- post-install-cmd, when a `composer install` command has finished.
+
+How do I set it up?
+-------------------
+
+Require this Composer plugin in your project template composer.json file:
+
+    "require": {
+      "drupal/core-project-message": "^8.8"
+    }
+
+### Configuration
+
+There are three ways to configure this plugin to output information:
+- Using a text file.
+- Using composer.json schema keys.
+- Embedding the information in the extra section of the composer.json file.
+
+### Using a text file
+
+By default, the plugin will respond to `post-install-cmd` or
+`post-create-project-cmd` Composer events by looking for a similarly-named file
+in the root of the project. For instance, if the user issues a `composer
+create-project` command, when that command is finished, the plugin will look for
+a file named `post-create-project-cmd-message.txt` and then display it on the
+command line.
+
+The file should be plain text, with markup suitable for Symfony's
+`OutputInterface::writeln()` method. See documentation here:
+https://symfony.com/doc/3.4/console/coloring.html
+
+You can also configure your own file(s), using the `extra` section of your
+composer.json file:
+
+    "extra": {
+      "drupal-core-project-message": {
+        "post-create-project-cmd-file": "bespoke/special_file.txt"
+      }
+    }
+
+### Using composer.json schema keys
+
+You can tell the plugin to output the structured support information from the
+composer.json file by telling it the keys you wish to display.
+
+Currently, only `name`, `description`, `homepage` and `support` are supported.
+
+    "extra": {
+        "drupal-core-project-message": {
+            "include-keys": ["homepage", "support"],
+        }
+    }
+
+Then you can include this information in your composer.json file, which you
+should probably be doing anyway.
+
+### Embedding the information in the extra section
+
+You can specify text directly within the `extra` section by using the
+`[event-name]-message` key. This message should be an array, with one string for
+each line:
+
+    "extra": {
+      "drupal-core-project-message": {
+        "post-create-project-cmd-message": [
+          "Thanks for installing this project.",
+          "Please visit our documentation here: http://example.com/docs"
+        ]
+      }
+    }
+
+These strings should be plain text, with markup suitable for Symfony's
+`OutputInterface::writeln()` method. See documentation here:
+https://symfony.com/doc/3.4/console/coloring.html
+
+The `-message` section will always override `-file` for a given event.
diff --git a/composer/Plugin/ProjectMessage/TESTING.txt b/composer/Plugin/ProjectMessage/TESTING.txt
new file mode 100644
index 000000000000..f3183ca01327
--- /dev/null
+++ b/composer/Plugin/ProjectMessage/TESTING.txt
@@ -0,0 +1,18 @@
+HOW-TO: Test this Drupal component
+
+In order to test this component, you'll need to get the entire Drupal repo and
+run the tests there.
+
+You'll find the tests under core/tests/Drupal/Tests/Plugin.
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can find more information about running PHPUnit tests with Drupal here:
+https://www.drupal.org/node/2116263
+
+Each component in the Drupal\Composer namespace has its own annotated test
+group. You can use this group to run only the tests for this component. Like
+this:
+
+$ ./vendor/bin/phpunit -c core --group ProjectMessage
diff --git a/composer/Plugin/ProjectMessage/composer.json b/composer/Plugin/ProjectMessage/composer.json
new file mode 100644
index 000000000000..e2884ab334e7
--- /dev/null
+++ b/composer/Plugin/ProjectMessage/composer.json
@@ -0,0 +1,20 @@
+{
+  "name": "drupal/core-project-message",
+  "description": "Adds a message after Composer installation.",
+  "keywords": ["drupal"],
+  "homepage": "https://www.drupal.org/project/drupal",
+  "license": "GPL-2.0-or-later",
+  "type": "composer-plugin",
+  "autoload": {
+    "psr-4": {
+      "Drupal\\Composer\\Plugin\\ProjectMessage\\": "."
+    }
+  },
+  "extra": {
+    "class": "Drupal\\Composer\\Plugin\\ProjectMessage\\MessagePlugin"
+  },
+  "require": {
+    "php": ">=7.0.8",
+    "composer-plugin-api": "^1.1"
+  }
+}
diff --git a/composer/Template/LegacyProject/composer.json b/composer/Template/LegacyProject/composer.json
index 45c53b076bbc..995e12bbd060 100644
--- a/composer/Template/LegacyProject/composer.json
+++ b/composer/Template/LegacyProject/composer.json
@@ -3,6 +3,11 @@
     "description": "Project template for Drupal 8 projects with composer following drupal/drupal layout",
     "type": "project",
     "license": "GPL-2.0-or-later",
+    "homepage": "https://www.drupal.org/project/drupal",
+    "support": {
+        "docs": "https://www.drupal.org/docs/user_guide/en/index.html",
+        "chat": "https://www.drupal.org/node/314178"
+    },
     "repositories": [
         {
             "type": "composer",
@@ -11,8 +16,9 @@
     ],
     "require": {
         "composer/installers": "^1.2",
-        "drupal/core-recommended": "^8.8",
         "drupal/core-composer-scaffold": "^8.8",
+        "drupal/core-project-message": "^8.8",
+        "drupal/core-recommended": "^8.8",
         "drupal/core-vendor-hardening": "^8.8"
     },
     "require-dev": {
@@ -41,6 +47,25 @@
             "drush/Commands/contrib/{$name}": ["type:drupal-drush"],
             "modules/custom/{$name}": ["type:drupal-custom-module"],
             "themes/custom/{$name}": ["type:drupal-custom-theme"]
+        },
+        "drupal-core-project-message": {
+            "include-keys": ["homepage", "support"],
+            "post-create-project-cmd-message": [
+                "<bg=blue;fg=white>                                                         </>",
+                "<bg=blue;fg=white>  Congratulations, you’ve installed the Drupal codebase  </>",
+                "<bg=blue;fg=white>  from the drupal/legacy-project template!               </>",
+                "<bg=blue;fg=white>                                                         </>",
+                "",
+                "<bg=yellow;fg=black>Next steps</>:",
+
+                "  * Install the site: https://www.drupal.org/docs/8/install",
+                "  * Read the user guide: https://www.drupal.org/docs/user_guide/en/index.html",
+                "  * Get support: https://www.drupal.org/support",
+                "  * Get involved with the Drupal community:",
+                "      https://www.drupal.org/getting-involved",
+                "  * Remove the plugin that prints this message:",
+                "      composer remove drupal/core-project-message"
+            ]
         }
     }
 }
diff --git a/composer/Template/RecommendedProject/composer.json b/composer/Template/RecommendedProject/composer.json
index cf5ff8b901d2..f6d2635af98c 100644
--- a/composer/Template/RecommendedProject/composer.json
+++ b/composer/Template/RecommendedProject/composer.json
@@ -3,6 +3,11 @@
     "description": "Project template for Drupal 8 projects with a relocated document root",
     "type": "project",
     "license": "GPL-2.0-or-later",
+    "homepage": "https://www.drupal.org/project/drupal",
+    "support": {
+        "docs": "https://www.drupal.org/docs/user_guide/en/index.html",
+        "chat": "https://www.drupal.org/node/314178"
+    },
     "repositories": [
         {
             "type": "composer",
@@ -11,8 +16,9 @@
     ],
     "require": {
         "composer/installers": "^1.2",
-        "drupal/core-recommended": "^8.8",
-        "drupal/core-composer-scaffold": "^8.8"
+        "drupal/core-composer-scaffold": "^8.8",
+        "drupal/core-project-message": "^8.8",
+        "drupal/core-recommended": "^8.8"
     },
     "require-dev": {
         "drupal/core-dev": "^8.8"
@@ -40,6 +46,25 @@
             "drush/Commands/contrib/{$name}": ["type:drupal-drush"],
             "web/modules/custom/{$name}": ["type:drupal-custom-module"],
             "web/themes/custom/{$name}": ["type:drupal-custom-theme"]
+        },
+        "drupal-core-project-message": {
+            "include-keys": ["homepage", "support"],
+            "post-create-project-cmd-message": [
+                "<bg=blue;fg=white>                                                         </>",
+                "<bg=blue;fg=white>  Congratulations, you’ve installed the Drupal codebase  </>",
+                "<bg=blue;fg=white>  from the drupal/recommended-project template!          </>",
+                "<bg=blue;fg=white>                                                         </>",
+                "",
+                "<bg=yellow;fg=black>Next steps</>:",
+
+                "  * Install the site: https://www.drupal.org/docs/8/install",
+                "  * Read the user guide: https://www.drupal.org/docs/user_guide/en/index.html",
+                "  * Get support: https://www.drupal.org/support",
+                "  * Get involved with the Drupal community:",
+                "      https://www.drupal.org/getting-involved",
+                "  * Remove the plugin that prints this message:",
+                "      composer remove drupal/core-project-message"
+            ]
         }
     }
 }
diff --git a/core/tests/Drupal/Tests/Composer/Plugin/ProjectMessage/ConfigTest.php b/core/tests/Drupal/Tests/Composer/Plugin/ProjectMessage/ConfigTest.php
new file mode 100644
index 000000000000..a9a8eff6f692
--- /dev/null
+++ b/core/tests/Drupal/Tests/Composer/Plugin/ProjectMessage/ConfigTest.php
@@ -0,0 +1,100 @@
+<?php
+
+namespace Drupal\Tests\Composer\Plugin\ProjectMessage;
+
+use Composer\Package\RootPackageInterface;
+use Drupal\Composer\Plugin\ProjectMessage\Message;
+use PHPUnit\Framework\TestCase;
+use org\bovigo\vfs\vfsStream;
+
+/**
+ * @coversDefaultClass Drupal\Composer\Plugin\ProjectMessage\Message
+ * @group ProjectMessage
+ */
+class ConfigTest extends TestCase {
+
+  public static function setUpBeforeClass() {
+    parent::setUpBeforeClass();
+    vfsStream::setup('config_test', NULL, [
+      'bespoke' => [
+        'special_file.txt' => "Special\nFile",
+      ],
+    ]);
+  }
+
+  public function provideGetMessageText() {
+    return [
+      [[], []],
+      [
+        ['Special', 'File'],
+        [
+          'drupal-core-project-message' => [
+            'event-name-file' => vfsStream::url('config_test/bespoke/special_file.txt'),
+          ],
+        ],
+      ],
+      [
+        ['I am the message.'],
+        [
+          'drupal-core-project-message' => [
+            'event-name-message' => ['I am the message.'],
+          ],
+        ],
+      ],
+      [
+        ['This message overrides file.'],
+        [
+          'drupal-core-project-message' => [
+            'event-name-message' => ['This message overrides file.'],
+            'event-name-file' => vfsStream::url('config_test/bespoke/special_file.txt'),
+          ],
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * @dataProvider provideGetMessageText
+   * @covers ::getText
+   */
+  public function testGetMessageText($expected, $config) {
+    // Root package has our config.
+    $root = $this->getMockBuilder(RootPackageInterface::class)
+      ->setMethods(['getExtra'])
+      ->getMockForAbstractClass();
+    $root->expects($this->once())
+      ->method('getExtra')
+      ->willReturn($config);
+
+    $message = new Message($root, 'event-name');
+
+    $this->assertSame($expected, $message->getText());
+  }
+
+  /**
+   * @covers ::getText
+   */
+  public function testDefaultFile() {
+    // Root package has no extra field.
+    $root = $this->getMockBuilder(RootPackageInterface::class)
+      ->setMethods(['getExtra'])
+      ->getMockForAbstractClass();
+    $root->expects($this->once())
+      ->method('getExtra')
+      ->willReturn([]);
+
+    // The default is to try to read from event-name-message.txt, so we expect
+    // config to try that.
+    $message = $this->getMockBuilder(Message::class)
+      ->setConstructorArgs([$root, 'event-name'])
+      ->setMethods(['getMessageFromFile'])
+      ->getMock();
+    $message->expects($this->once())
+      ->method('getMessageFromFile')
+      ->with('event-name-message.txt')
+      ->willReturn([]);
+
+    $this->assertSame([], $message->getText());
+  }
+
+}
-- 
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