Issue #3134648 by alexpott, dww, greg.1.anderson, hussainweb, catch, …

…xjm, Mixologic: [backport, needs scheduling] Don't pin the composer/installers version in drupal/core-recommended

tests/Drupal/Tests/Composer/Generator/Fixtures.php

@@ -33,6 +33,7 @@ protected function composerJson() {
       'license' => 'GPL-2.0-or-later',
       'require' =>
       [
+        'composer/installers' => '^1.9',
         'php' => '>=7.0.8',
         'symfony/yaml' => '~3.4.5',
       ],
@@ -59,6 +60,15 @@ protected function composerLock() {
       'content-hash' => 'da9910627bab73a256b39ceda83d7167',
       'packages' =>
       [
+        [
+          'name' => "composer/installers",
+          'version' => 'v1.9.0',
+          'source' => [
+            'type' => 'git',
+            'url' => 'https://github.com/composer/installers.git',
+            'reference' => 'b93bcf0fa1fccb0b7d176b0967d969691cd74cca',
+          ],
+        ],
         [
           'name' => 'symfony/polyfill-ctype',
           'version' => 'v1.12.0',

tests/Drupal/Tests/Composer/Generator/OverlapWithTopLevelDependenciesTest.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace Drupal\Tests\Composer\Generator;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Tests DrupalCoreRecommendedBuilder.
+ *
+ * @group Metapackage
+ */
+class OverlapWithTopLevelDependenciesTest extends TestCase {
+
+  /**
+   * Provides data for testOverlapWithTemplateProject().
+   */
+  public function templateProjectPathProvider() {
+    return [
+      [
+        'composer/Template/RecommendedProject',
+      ],
+      [
+        'composer/Template/LegacyProject',
+      ],
+    ];
+  }
+
+  /**
+   * Tests top level and core-recommended dependencies do not overlap.
+   *
+   * @dataProvider templateProjectPathProvider
+   *
+   * @param string $template_project_path
+   *   The path of the project template to test.
+   */
+  public function testOverlapWithTemplateProject($template_project_path) {
+    $root = dirname(__DIR__, 6);
+    // Read template project composer.json.
+    $top_level_composer_json = json_decode(file_get_contents("$root/$template_project_path/composer.json"), TRUE);
+
+    // Read drupal/core-recommended composer.json.
+    $core_recommended_composer_json = json_decode(file_get_contents("$root/composer/Metapackage/CoreRecommended/composer.json"), TRUE);
+
+    // Fail if any required project in the require section of the template
+    // project also exists in core/recommended.
+    foreach ($top_level_composer_json['require'] as $project => $version_constraint) {
+      $this->assertArrayNotHasKey($project, $core_recommended_composer_json['require'], "Pinned project $project is also a top-level dependency of $template_project_path. This can expose a Composer bug. See https://www.drupal.org/project/drupal/issues/3134648 and https://github.com/composer/composer/issues/8882");
+    }
+  }
+
+}