Add hint in create-project when it fails due to a missing allow-plugins in project, refs #10928

src/Composer/Command/CreateProjectCommand.php

@@ -26,6 +26,7 @@ use Composer\DependencyResolver\Operation\InstallOperation;
 use Composer\Package\Version\VersionSelector;
 use Composer\Package\AliasPackage;
 use Composer\Pcre\Preg;
+use Composer\Plugin\PluginBlockedException;
 use Composer\Repository\RepositoryFactory;
 use Composer\Repository\CompositeRepository;
 use Composer\Repository\PlatformRepository;
@@ -268,10 +269,16 @@ EOT
                 $installer->disablePlugins();
             }
 
+            try {
                 $status = $installer->run();
                 if (0 !== $status) {
                     return $status;
                 }
+            } catch (PluginBlockedException $e) {
+                $io->writeError('<error>Hint: To allow running the config command recommended below before dependencies are installed, run create-project with --no-install.</error>');
+                $io->writeError('<error>You can then cd into '.getcwd().', configure allow-plugins, and finally run a composer install to complete the process.</error>');
+                throw $e;
+            }
         }
 
         $hasVcs = $installedFromVcs;

src/Composer/Plugin/PluginBlockedException.php

@@ -0,0 +1,19 @@
+<?php
+
+/*
+ * This file is part of Composer.
+ *
+ * (c) Nils Adermann <naderman@naderman.de>
+ *     Jordi Boggiano <j.boggiano@seld.be>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Composer\Plugin;
+
+use UnexpectedValueException;
+
+class PluginBlockedException extends UnexpectedValueException
+{
+}

src/Composer/Plugin/PluginManager.php

@@ -765,7 +765,7 @@ class PluginManager
             }
         }
 
-        throw new \UnexpectedValueException(
+        throw new PluginBlockedException(
             $package.($isGlobalPlugin ? ' (installed globally)' : '').' contains a Composer plugin which is blocked by your allow-plugins config. You may add it to the list if you consider it safe.'.PHP_EOL.
             'You can run "composer '.($isGlobalPlugin ? 'global ' : '').'config --no-plugins allow-plugins.'.$package.' [true|false]" to enable it (true) or disable it explicitly and suppress this exception (false)'.PHP_EOL.
             'See https://getcomposer.org/allow-plugins'