Added Composer script to allow contrib modules to be installed on 11.x.

Fixes #23.

composer.json

@@ -66,6 +66,9 @@
         ],
         "post-drupal-scaffold-cmd": [
             "DrupalGitCloneProject\\ComposerScripts::postDrupalScaffold"
+        ],
+        "pre-pool-create": [
+            "DrupalGitCloneProject\\ComposerCoreVersionsLeniency::prePoolCreate"
         ]
     },
     "autoload": {

src/ComposerCoreVersionsLeniency.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace DrupalGitCloneProject;
+
+use Composer\Package\Link;
+use Composer\Package\CompletePackage;
+use Composer\Plugin\PrePoolCreateEvent;
+use Composer\Semver\VersionParser;
+
+// Development: this makes symfony var-dumper work.
+// See https://github.com/composer/composer/issues/7911
+// include_once './vendor/symfony/var-dumper/Resources/functions/dump.php';
+
+/**
+ * Provides Composer scripts to allow installation on core 11.x.
+ *
+ * Inspired by mglaman/composer-drupal-lenient.
+ */
+class ComposerCoreVersionsLeniency {
+
+  /**
+   * Act on pre-pool-create event.
+   *
+   * This tweaks the core requirement of contrib modules, so that Composer will
+   * install them when the Drupal core git clone is checked out to the 11.x
+   * branch.
+   *
+   * @param \Composer\Plugin\PrePoolCreateEvent $event
+   *   The event.
+   */
+  public static function prePoolCreate(PrePoolCreateEvent $event) {
+    // @todo Only act if the current branch of drupal/core is 11.x
+
+    $version_parser = new VersionParser();
+
+    $packages = $event->getPackages();
+    foreach ($packages as $package) {
+      $type = $package->getType();
+      if ($type === 'drupal-core') {
+        continue;
+      }
+
+      if ($type != 'drupal-module') {
+        continue;
+      }
+
+      $requires = $package->getRequires();
+
+      if (!isset($requires['drupal/core'])) {
+        continue;
+      }
+
+      $drupal_core_require = $requires['drupal/core'];
+
+      $pretty_constraint = $drupal_core_require->getPrettyConstraint();
+      if (str_contains($pretty_constraint, '^11')) {
+        continue;
+      }
+
+      // Make a new constraint with the 11 requirement appended.
+      $pretty_constraint_with_11 = $pretty_constraint . ' || ^11';
+      $constraint_with_11 = $version_parser->parseConstraints($pretty_constraint_with_11);
+
+      // Replace the existing core requirement with the new one.
+      $requires['drupal/core'] = new Link(
+        $drupal_core_require->getSource(),
+        $drupal_core_require->getTarget(),
+        $constraint_with_11,
+        $drupal_core_require->getDescription(),
+        $constraint_with_11->getPrettyString(),
+      );
+
+      // No idea why we need to check CompletePackage, just aping
+      // mglaman/composer-drupal-lenient.
+      if ($package instanceof CompletePackage) {
+        // @note `setRequires` is on Package but not PackageInterface.
+        $package->setRequires($requires);
+      }
+    }
+  }
+
+}

src/ComposerScripts.php

@@ -4,6 +4,10 @@
 
 use Composer\Script\Event;
 
+// Development: this makes symfony var-dumper work.
+// See https://github.com/composer/composer/issues/7911
+// include_once './vendor/symfony/var-dumper/Resources/functions/dump.php';
+
 /**
  * Provides Composer scripts for setting up Drupal from a git clone.
  */