Issue #3302654 by bnjmnm, xjm, quietone, lauriii, phenaproxima: Create Starterkit readme

(cherry picked from commit 7e4c0f96)

core/lib/Drupal/Core/Command/GenerateTheme.php

@@ -97,6 +97,13 @@ protected function execute(InputInterface $input, OutputInterface $output): int
     $tmp_dir = $this->getUniqueTmpDirPath();
     $this->copyRecursive($source, $tmp_dir);
 
+    // Readme is specific to Starterkit, so remove it from the generated theme.
+    $readme_file = "$tmp_dir/README.md";
+    if (!file_put_contents($readme_file, "$destination_theme theme, generated from $source_theme_name. Additional information on generating themes can be found in the [Starterkit documentation](https://www.drupal.org/docs/core-modules-and-themes/core-themes/starterkit-theme).")) {
+      $io->getErrorStyle()->error("The readme could not be rewritten.");
+      return 1;
+    }
+
     // Rename files based on the theme machine name.
     $file_pattern = "/$source_theme_name\.(theme|[^.]+\.yml)/";
     if ($files = @scandir($tmp_dir)) {

core/tests/Drupal/Tests/Core/Command/GenerateThemeTest.php

@@ -99,6 +99,10 @@ public function test() {
     self::assertArrayHasKey('generator', $info);
     self::assertEquals('starterkit_theme:9.4.0', $info['generator']);
 
+    // Confirm readme is rewritten.
+    $readme_file = $this->getWorkspaceDirectory() . "/$theme_path_relative/README.md";
+    $this->assertSame('test_custom_theme theme, generated from starterkit_theme. Additional information on generating themes can be found in the [Starterkit documentation](https://www.drupal.org/docs/core-modules-and-themes/core-themes/starterkit-theme).', file_get_contents($readme_file));
+
     // Ensure that the generated theme can be installed.
     $this->installQuickStart('minimal');
     $this->formLogin($this->adminUsername, $this->adminPassword);
@@ -121,6 +125,40 @@ public function test() {
     $this->assertFileDoesNotExist($theme_path_absolute . '/test_custom_theme.theme');
   }
 
+  /**
+   * Tests generating a theme from another Starterkit enabled theme.
+   */
+  public function testGeneratingFromAnotherTheme() {
+    // Do not rely on \Drupal::VERSION: change the version to a concrete version
+    // number, to simulate using a tagged core release.
+    $starterkit_info_yml = $this->getWorkspaceDirectory() . '/core/themes/starterkit_theme/starterkit_theme.info.yml';
+    $info = Yaml::decode(file_get_contents($starterkit_info_yml));
+    $info['version'] = '9.4.0';
+    file_put_contents($starterkit_info_yml, Yaml::encode($info));
+
+    $process = $this->generateThemeFromStarterkit();
+    $exit_code = $process->run();
+    $this->assertSame('Theme generated successfully to themes/test_custom_theme', trim($process->getOutput()), $process->getErrorOutput());
+    $this->assertSame(0, $exit_code);
+    $install_command = [
+      $this->php,
+      'core/scripts/drupal',
+      'generate-theme',
+      'generated_from_another_theme',
+      '--name="Generated from another theme"',
+      '--description="Custom theme generated from a theme other than starterkit_theme"',
+      '--starterkit=test_custom_theme',
+    ];
+    $process = new Process($install_command);
+    $exit_code = $process->run();
+    $this->assertSame('Theme generated successfully to themes/generated_from_another_theme', trim($process->getOutput()), $process->getErrorOutput());
+    $this->assertSame(0, $exit_code);
+
+    // Confirm readme is rewritten.
+    $readme_file = $this->getWorkspaceDirectory() . '/themes/generated_from_another_theme/README.md';
+    $this->assertSame('generated_from_another_theme theme, generated from test_custom_theme. Additional information on generating themes can be found in the [Starterkit documentation](https://www.drupal.org/docs/core-modules-and-themes/core-themes/starterkit-theme).', file_get_contents($readme_file));
+  }
+
   /**
    * Tests the generate-theme command on a dev snapshot of Drupal core.
    */

core/themes/starterkit_theme/README.md

+# Starterkit Theme
+
+## How to use Starterkit
+The Starterkit theme is not directly used by Drupal, nor is it used as a base theme.
+**Starterkit is for generating new themes** that include
+reasonably un-opinionated templates and styles that eliminate much of the
+the initial work required to create a theme.
+
+Starterkit is the recommended approach for creating new themes. For more
+information, consult the
+[Starterkit documentation on Drupal.org](https://www.drupal.org/docs/core-modules-and-themes/core-themes/starterkit-theme).